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Research Article
CO Poisoning of Ru Catalysts in CO2 Hydrogenation under Thermal and Plasma Conditions: A Combined Kinetic and Diffuse Reflectance Infrared Fourier Transform Spectroscopy–Mass Spectrometry StudyClick to copy article linkArticle link copied!
- Shanshan XuShanshan XuDepartment of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Shanshan Xu
- Sarayute ChansaiSarayute ChansaiDepartment of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Sarayute Chansai
- Shaojun XuShaojun XuUK Catalysis Hub, Research Complex at Harwell, Didcot OX11 0FA, United KingdomCardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, United KingdomMore by Shaojun Xu
- Cristina E. StereCristina E. StereDepartment of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Cristina E. Stere
- Yilai JiaoYilai JiaoShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, ChinaMore by Yilai Jiao
- Sihai YangSihai YangDepartment of Chemistry, School of Natural Science, The University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Sihai Yang
- Christopher Hardacre*Christopher Hardacre*Email: [email protected]Department of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Christopher Hardacre
- Xiaolei Fan*Xiaolei Fan*Email: [email protected]Department of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Xiaolei Fan
Abstract
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Plasma-catalysis systems are complex and require further understanding to advance the technology. Herein, CO poisoning in CO2 hydrogenation over supported ruthenium (Ru) catalysts in a nonthermal plasma (NTP)-catalysis system was investigated by a combined kinetic and diffuse reflectance infrared Fourier transform spectroscopy–mass spectrometry (DRIFTS–MS) study and compared with the thermal catalytic system. The relevant findings suggest the coexistence of the Langmuir–Hinshelwood and Eley–Rideal mechanisms in the NTP-catalysis. Importantly, comparative study of CO poisoning of the Ru catalyst was performed under the thermal and NTP conditions, showing the advantage of the hybrid NTP-catalysis system over the thermal counterpart to mitigate CO poisoning of the catalyst. Specifically, compared with the CO poisoning in thermal catalysis due to strong CO adsorption and associated metal sintering, in situ DRIFTS–MS analysis revealed that the collisions of reactive plasma-derived species in NTP-catalysis could remove the strongly adsorbed carbon species to recover the active sites for CO2 activation. Thus, the NTP-catalysis was capable of preventing CO poisoning of the Ru catalyst in CO2 hydrogenation. Additionally, under the NTP conditions, the NTP-enabled water-gas shift reaction of CO with H2O (which was produced by CO/CO2 hydrogenation) shifted the equilibrium of CO2 hydrogenation toward CH4 production.
Copyright © 2020 American Chemical Society
1. Introduction
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Hybrid nonthermal plasma (NTP) and catalysis (NTP-catalysis) systems can activate and convert a variety of stable molecules, such as carbon dioxide (CO2), methane (CH4), and nitrogen (N2), into desired products under mild conditions, e.g., ambient pressure and low bulk gas temperatures (<200 °C), (1−3) but the hybrid system is highly complex. NTP-catalysis is particularly beneficial to enable kinetically and/or thermodynamically limited reactions, including dry reforming of methane, (4) water-gas shift, (5,6) and CO2 hydrogenation. (7) In comparison with the thermal counterparts, NTP-catalysis has shown the capability of lowering the energy barrier required for the catalysis and/or changing the reaction pathways on the catalyst surface. (8,9) Recent studies have shown that, being similar with the thermal catalysis, the intrinsic nature of heterogeneous catalysts (including the supports), such as metal dispersion and pore structure, plays a key role in NTP-catalysis. For example, a series of Ni supported on silicalite-1 (with different pore structures) catalysts was designed to study CO2 hydrogenation under NTP conditions. It was found that the pore structure of the silicalite-1 supports determines the dispersion and location of Ni sites and, hence, the accessibility of plasma-generated reactive species, thus affecting the performance of the NTP-catalysis. (10)
In addition to the activity, the stability and longevity of the catalysts are important factors for practical catalysis under both thermal and NTP conditions. Under thermal conditions during CO2 hydrogenation, catalyst deactivation is mainly caused by (i) metal particle sintering due to high reaction temperatures, (ii) coking caused by carbon deposition, and (iii) catalyst poisoning resulting from trace impurities in the feed gases such as carbon monoxide (CO). Due to the low-temperature activation of catalytic process, NTP-assisted CO2 hydrogenation intrinsically avoids sintering and coking processes. (9) Regarding catalyst poisoning, specifically CO2 hydrogenation, it is well known that CO poisoning is one of the worst catalyst-deactivating processes under thermal conditions. (11,12) Under plasma conditions, conversely, previous studies have shown that the plasma could enable the recovery of poisoned catalytic sites via dynamic collisions among reactive plasma-derived species, which lead to the desorption of strongly bound surface species. (13,14) Accordingly, insights into CO poisoning under thermal and NTP conditions, especially relevant deactivation mechanisms, need to be assessed to develop mature NTP-catalysis technology for potential practical adoptions. NTP-catalysis is a complex combination of plasma discharge and surface reactions (and other factors) with multifaceted interplays between them. Regarding the surface reactions under NTP conditions, in situ techniques, such as diffuse reflectance infrared Fourier transform (DRIFTS) (7,9) and extended X-ray absorption fine structure (EXAFS) spectroscopy, (15) have been proved to be powerful tools to gain insights into the surface dynamics of the catalyst, reaction mechanisms, and the catalyst state during NTP-catalysis, which can facilitate the rational design of bespoke catalysts for NTP conditions. However, relevant in situ studies of NTP-catalysis toward the understanding of catalyst poisoning are still lacking.
This work presents the comparative study of the effect of CO on CO2 hydrogenation over a supported Ru catalyst (i.e., CO poisoning) under thermal and NTP conditions. The intrinsic nature of the catalysts on the performance of CO2 hydrogenation was first studied, and the Ru/SiO2 catalyst with high activity and stability was chosen for further investigation. To elucidate the mechanism of CO poisoning, the mechanistic investigation of CO2 hydrogenation including the kinetic and in situ DRIFTS studies was comparatively performed under thermal and NTP conditions, which provide useful information on the intermediates and reaction pathways of CO2 hydrogenation. Finally, the mechanism of CO poisoning in CO2 hydrogenation over the Ru/SiO2 catalyst was investigated. Under the thermal conditions, significant catalyst deactivation due to the strong CO adsorption and metal sintering was observed; conversely, NTP activation was found to mitigate the effect of CO on the performance of the catalyst and regenerate the catalyst efficiently.
2. Experimental Section
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2.1. Preparation and Characterization of Catalysts
Ruthenium (III) chloride trihydrate (RuCl3·3H2O), silicon dioxide, and γ-Al2O3 were purchased from Sigma-Aldrich and used without further purification.
Supported Ru catalysts including Ru/SiO2 and Ru/γ-Al2O3 (with the theoretical metal loading of 2 wt %) were prepared using the wet impregnation method. First, the support (1.5 g) was suspended in water (30 mL), and then 6.2 mL of RuCl3·3H2O solution (10 mg mL–1) was added dropwise. The mixture was vigorously stirred for 3 h and then evaporated using a rotary evaporator. The resulting precipitate was dried at 70 °C in a convection oven for 12 h. The obtained dry solid was subsequently reduced in pure H2 at 300 °C for 2 h with a heating rate of 5 °C min–1. After reduction, the sample was cooled down to room temperature (RT) naturally under the H2 flow (at 100 mL min–1). The actual metal loading was determined by inductively coupled plasma optical emission spectrometry (ICP-OES; Supporting information). The prepared catalysts were characterized to understand their physical and chemical properties by bright-field transmission electron microscopy (TEM), N2 physisorption (using the Brunauer–Emmett–Teller (BET) method), hydrogen temperature programmed reduction (H2-TPR), and CO chemisorption, and the relevant experimental details are provided in the Supporting Information.
2.2. Catalysis
A dielectric barrier discharge (DBD) flow reactor was used for NTP-activated CO2 hydrogenation, which is depicted in Figure S1, and the details of the DBD reactor have been described elsewhere. (9) Parameters of the NTP-catalysis system were measured using an oscilloscope (Tektronix TBS1072B) connected with a high-voltage probe (Tektronix, P6015) and current monitor. NTP-catalysis was performed at atmospheric pressure without a heating source. Briefly, ∼100 mg of catalyst (pellet sizes of 250–425 μm) was packed into a quartz tube (6 mm o.d. × 4 mm i.d.), where an aluminum foil wrapped outside of the tube served as the high-voltage electrode and a tungsten rod (1 mm o.d.) in the center of reactor acted as the ground electrode. Since the catalyst was exposed to air at RT before being loaded to the DBD reactor, it was treated in situ by NTP (at 6.5 kV) using 50% H2/Ar as the discharge gas for 20 min before catalysis. The feed of CO2, H2, and Ar balance (molar ratio of 1:3:3) was introduced by mass flow controllers (Bronkhorst, F-201CV-500-RAD-11-V) with the flowrate of 50 mL min–1. The applied voltage was from 5.5 to 7.5 kV at a constant frequency of 21.0 kHz. The product was analyzed by using online mass spectrometry (MS, Hiden HPR-20) and two-channel online gas chromatography (GC) equipped with a Porapak Q packed column, thermal conductivity detector (TCD), and flame ionization detector (FID). An Ar balance was used in the system to avoid the signal saturation of MS signal. For each measurement, three samples of gas products were analyzed under steady-state conditions for an average value and error determination. Control experiments using the empty reactor (catalyst-free) and the reactor with the bare supports as a packing were performed under the same NTP conditions.
CO poisoning study under the NTP condition (at 6.5 kV and 21.0 kHz) was investigated by varying the inlet molar ratio of CO/CO2 between 0 and 2. The total gas feed flowrate was 50 mL min–1, corresponding to a space velocity of 30,000 mL (STP) gcat–1 h–1, which included CO2, CO, H2, and Ar balance (molar ratio of H2/(CO2 + CO) = 3). Catalyst deactivation was monitored as a function of time-on-stream (ToS) by switching the CO on and off in the feed. The average bulk temperature of the system between 5.5 and 7.5 kV was measured using an infrared (IR) thermometer and was in the range of 110–135 °C. Specifically, the average bulk temperature at 6.5 kV was ∼129 °C, which could not activate CO2 conversion thermally, according to a previous study. (9)
For comparison, thermal catalysis was carried out at 250–430 °C at atmospheric pressure. Prior to catalysis, the catalyst (pellets, about 100 mg) was first treated at 300 °C for 1 h in 50% H2/Ar. Then, the feed (CO2/H2/Ar = 1:3:3) was introduced into the reactor at 50 mL min–1. The temperature of the catalyst bed was monitored by a K-type thermocouple embedded in the catalyst bed.
CO poisoning of the catalyst under the thermal condition (at 330 °C) was studied using the same gas condition as in the relevant NTP-catalysis. The catalyst deactivation experiment was performed at 330 °C with the same gas conditions as described in the NTP-catalysis (for CO poisoning study).
CO2 (XCO2) conversion, CO (XCO) conversion, carbon (XC = XCO2 + XCO) conversion, selectivity toward CH4 (SCH4), and CH4 yield (YCH4) were determined accordingly to evaluate the catalytic performance (all the performance parameters are defined in the Supporting Information).
2.3. Kinetic Study
The kinetic study of thermal catalysis was performed at 260–320 °C with ∼30 mg of catalyst (diluted with inert glass beads to prevent hot spots) to ensure low CO2 conversions of <20%. The feed mixture containing CO2/H2/Ar (molar ratio = 1:3:3) was fed into the reactor for the kinetic study. To extract the reaction order with respect to H2 and CO2 partial pressures, the composition of the feed was varied; i.e., H2 partial pressure was changed with a constant partial pressure of CO2 and vice versa.
Kinetic study of the NTP-catalysis was performed using similar procedures and conditions as described above (about 30 mg of catalyst diluted with glass beads, at 5.0–6.5 kV and 21.0 kHz). The gas conditions were the same as in the kinetic study of the thermal catalysis. Due to the low bulk temperature under the NTP conditions (<129 °C), thermal activation of CO2 was not possible. Considering the effect of support packing and discharge volume, control experiments using the same amount of the bare supports and inert glass beads were performed to extract the information on the relevant gas phase and surface (over the bare supports) reactions under NTP, which was subsequently used to correct the kinetic data of the NTP-catalysis (Supporting Information).
2.4. In Situ DRIFTS–MS
The experimental setup of DRIFTS–MS for NTP-catalysis was described elsewhere. (9) The catalyst was pretreated with 50% H2/Ar gas under NTP at 6.0 kV and 27.0 kHz for 20 min in the flow cell. Then, the gas mixture containing CO2, CO, H2, and Ar balance was fed into the cell for the reaction. Kr at 10 mL min–1 was also introduced as the internal standard. The use of Ar balance in DRIFTS experiments was to avoid the signal saturation of IR spectra and MS signal. NTP-catalysis in the DRIFTS cell was performed at a constant peak voltage of 5.5 kV to avoid arcing between the electrodes. The IR spectra were recorded every 60 s with a resolution of 4 cm–1 and analyzed by OPUS software.
3. Results and Discussion
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3.1. Effect of Catalysts in the NTP-Catalysis
CO2 hydrogenation over the two supported Ru catalysts under NTP conditions was investigated in reference to the control experiments (i.e., the empty tube for NTP-alone experiments and the reactor with the bare γ-Al2O3 and SiO2 support packing under the NTP conditions) to screen the candidate for the following study (as shown in Figure 1). Under the NTP conditions without a catalyst, CO2 was decomposed to CO with a trivial conversion of ∼6% at 6.5 kV (with the specific input energy (SIE) of 2.0 J mL–1). Similarly, NTP systems with the bare γ-Al2O3 and SiO2 supports were only selective to CO with relevant CO2 conversions of ∼13 and ∼15%, respectively, at 6.5 kV. In comparison with the system without a packing, that is, the blank experiment with an empty tube, the higher CO2 conversions with the bare supports can be attributed to the enhanced average electric field strength, benefiting CO2 dissociation. (16) Conversely, in NTP-catalysis with the voltage above 7.0 kV (SIE > 2.5 J mL–1), regardless of the Ru catalysts used in this work, CO2 conversion and CH4 yield increased significantly to >57%. However, Ru catalysts based on different supports showed different behaviors under the NTP conditions, demonstrating the effect of catalyst design on NTP-catalysis. (17) Specifically, the Ru/SiO2 catalyst showed a higher activity as compared with the Ru/γ-Al2O3 catalyst, especially at the lower voltage of <6.5 kV (SIE < 2.5 J mL–1). The highest CO2 conversion (∼65%) and CH4 yield (∼63%) at 6.5 kV were achieved by Ru/SiO2, while the Ru/γ-Al2O3 catalyst only showed about 35% CO2 conversion and 29% CH4 yield, being less active for NTP-activated CO2 hydrogenation. Similarly, under thermal conditions (Figure S2), Ru/SiO2 outperformed Ru/γ-Al2O3 as well, suggesting that the intrinsic nature of catalysts dominated the performance of CO2 hydrogenation regardless of the means of activation. In detail, the corresponding TEM and CO chemisorption analysis of the Ru/SiO2 and Ru/γ-Al2O3 catalysts (Figure S3 and Table S3) showed that the two catalysts presented similar average particle sizes and Ru dispersions. Additionally, the metal–support interaction of the two catalysts was also similar, as revealed by H2-TPR (Figure S5). These findings show that the property of the supported active Ru phases of the two catalysts under study is similar, thus suggesting that the supported Ru might not affect the activity of the two catalysts significantly under NTP conditions.
Figure 1
Figure 1. Performance of NTP-activated catalytic CO2 hydrogenation as a function of voltage/input energy over the Ru/SiO2 and Ru/γ-Al2O3 catalysts in reference to the control experiments; (a) CO2 conversion and (b) CH4 yield. Experimental conditions: feed gas composition of CO2/H2/Ar = 1:3:3 and WHSV of 30,000 mL (STP) gcat–1 h–1.
Under NTP conditions, the effect of dielectric property of the bare supports on the catalysis was deemed insignificant since γ-Al2O3 and SiO2 have different dielectric constants (∼9.1 and ∼4.2, respectively), while the reaction results were similar. (18) In addition to the dielectric constant, the porous property of the packing material can also influence the plasma discharge and reaction performance under the NTP conditions. (19) N2 physisorption analysis showed that the Ru/SiO2 catalyst and Ru/γ-Al2O3 catalyst had comparable pore volumes of ∼0.7 cm3 g–1. The average pore sizes of the Ru/SiO2 catalyst and Ru/γ-Al2O3 catalyst were ∼5 and ∼12 nm, respectively, which are much smaller than the Debye length, suggesting that the penetration of plasma into the catalyst pores might be limited. However, a previous study based on Monte Carlo calculation revealed that microdischarges might be formed near the pores of mesoporous catalysts with mesopore sizes of 2–50 nm, and the relatively high surface area promoted the intensified surface discharge on the surface. (20) This may explain the better catalytic performance of Ru/SiO2 in CO2 hydrogenation than Ru/γ-Al2O3 since the high surface area might promote the surface discharge in NTP-catalysis. The Ru/SiO2 catalyst has a well-developed micro/mesoporous structure with a higher specific BET surface area of 557 m2 g–1 than that of the Ru/γ-Al2O3 catalyst (239 m2 g–1). Thus, a high surface area is expected as the key to determine the catalytic performance of the supported Ru catalysts under NTP and thermal conditions. The calculated apparent activation energy (Figure S6) showed that the Ru/SiO2 catalyst presented lower values, under both conditions, than the Ru/γ-Al2O3 catalyst (Table S4), e.g., 20 kJ mol–1 versus 71 kJ mol–1 in NTP-catalysis (details of the kinetic calculations are presented in the Supporting Information). (8,9)
3.2. Comparative Mechanistic Study of CO2 Hydrogenation over Ru/SiO2
Preliminary catalytic assessments have shown that the Ru/SiO2 catalyst presented relatively high CO2 conversion and CH4 yield for CO2 hydrogenation under NTP and thermal conditions (in comparison with the Ru/γ-Al2O3 catalyst); thus, the Ru/SiO2 catalyst was selected for further investigation. To gain insight into the mechanism of CO poisoning in CO2 conversions, first, the comparatively mechanistic study of CO2 hydrogenation over the Ru/SiO2 catalyst was performed. Figure 2 and Table 1 show correlation between the apparent reaction rate and the CO2/H2 partial pressures (pH2 and pCO2) in CO2 hydrogenation under the thermal and NTP conditions. Under the thermal condition at 330 °C, the CH4 formation rate over the Ru/SiO2 catalyst showed a stronger dependence on pH2 than pCO2 in the feed. Specifically, the reaction order with respect to pH2 was calculated as 1.0, in line with the Langmuir–Hinshelwood mechanism. (21) A previous study showed that H2 dissociation on the Ru surface was fast with the produced Had being short-lived, (22) and the reaction order regarding pH2 indicated that CO2 and H2 were adsorbed on the different active sites on the Ru surface. (23,24) The reaction order regarding pCO2 was found to be −0.03, which can be approximated as zero order, suggesting that CO2 concentration has a relatively weak influence on the formation rate of CH4. This finding suggested (i) the CO2 chemisorption on the catalyst and (ii) the saturation of relevant active sites on the Ru surface by CO2 molecules at relatively low CO2 concentrations. (22) Therefore, under the thermal condition, CO2 participated in the reaction via the Langmuir–Hinshelwood mechanism, i.e., CO2 adsorbed on the catalyst, and then dissociated to active intermediates under heating, which further react with Had to form methane.
Figure 2
Figure 2. Dependence of the reaction rate on pH2 and pCO2 under (a, c) thermal conditions (at 330 °C) and (b, d) NTP conditions.
Table 1. Reaction Order with Respect to pH2 and pCO2 for Catalytic CO2 Hydrogenation over Ru/SiO2 under the Thermal (at 330 °C) and NTP Conditions
| NTP | ||||
|---|---|---|---|---|
| reaction order | 6.0 kV | 6.5 kV | 7.0 kV | thermal |
| pH2 | 1.40 | 1.60 | 1.50 | 1.0 |
| pCO2 | 0.30 | 0.30 | 0.25 | –0.03 |
In comparison, under the NTP conditions, the reaction orders with respect to pH2 and pCO2 were 1.50 ± 0.10 and 0.30 ± 0.05, respectively. Additionally, both reaction orders remained almost constant as a function of the input power, suggesting the same surface reaction mechanism at different input powers. The comparatively strong dependence on pH2 and pCO2 under NTP conditions (compared with the thermal condition) indicates the presence of multiple reaction pathways for CO2 hydrogenation in NTP-catalysis. In addition to the surface reactions under the thermal catalysis, the vibrationally activated and dissociated active species (e.g., electronically excited H radical) in the gas-phase reaction under NTP conditions might also participate in the surface hydrogenation reactions via the Eley–Rideal mechanism. (25) To clarify the relationship between the reaction order and reaction mechanism under NTP and thermal conditions, in situ DRIFTS–MS was performed, and the relevant results were correlated with the kinetic data.
In situ DRIFTS coupled with MS characterization of CO2 hydrogenation over the Ru/SiO2 catalyst was comparatively performed under thermal and NTP conditions to investigate the mechanism of CO2 hydrogenation. Under the thermal condition at 250 °C (Figure S7), characteristic peaks of surface hydroxyls (OHad, from ∼3596 to ∼3730 cm–1), CHx species (CH3,ad, at ∼3015 cm–1), carbonyl (COad, at ∼1997 cm–1), and surface-adsorbed CH4 (at ∼3047 cm–1) were detected on the catalyst surface. It was observed that after changing the feed to inert Ar, the COad band decreased slowly (within 10 min, Figure S7b), whereas the intensity of methane decreased rapidly (Figure S7c), suggesting that the gradual decrease of COad band was only due to the desorption under the condition used. Conversely, when the feed was changed to H2, the intensity of COad band declined fast (within 2 min) with the associated rapid emergence of peak in the CH4 signal, which gradually decreased after 2 min. This phenomenon confirms COad as the active intermediate, which further reacted with H2 to produce CH4, being in line with the kinetic data discussed above (Figure 2). Under thermal conditions, catalytic CO2 hydrogenation is commonly thought to proceed via a direct carbon–oxygen bond dissociation mechanism, (26,27) which involves the dissociation of CO2 on the catalyst surface (to adsorbed COad and surface C) and the subsequent hydrogenation of surface C. Under the thermal condition used in this work, DRIFTS only probed COad species on the Ru surface, confirming the direct carbon–oxygen bond dissociation mechanism.
Under the NTP condition with a CO2/Ar mixture, the gas-phase CO2 dissociation was confirmed, as shown in Figure S8. With the NTP on (Figure S8b), the linearly and bridged adsorbed COad species (at ∼2092, 2041, and 1881 cm–1) and bidentate and monodentate carbonate (at ∼1274 and ∼1311 cm–1, respectively) were measured. Since carbonate species were not observed under the thermal condition, the presence of carbonate species under the NTP condition was due to the plasma excitation and could be ascribed to the adsorption of vibrationally excited CO2 species on the catalyst surface.
Under the NTP-off condition, with the reaction gas feed (i.e., 3% CO2/9% H2/Ar), in addition to the CO2 gas-phase peak (at ∼2360 and 2342 cm–1, as shown in Figure 3a), surface carbon species were not detected by DRIFTS and no reaction was observed (according to MS). Upon the ignition of plasma, the MS profile showed the instantaneous appearance of CH4 signal (Figure S9a), confirming the formation of CH4 over the catalyst under NTP activation. At the same time, surface formyl species (CHxO, at about 1284, 1270, and 1111 cm–1) and carbonyl species (i.e., linearly adsorbed COad on Ru0 at 2034 cm–1 and linear form Ruδ+-CO at 2084 cm–1), (28) as shown in Figure 3b, were measured by DRIFTS. Compared with the COad bands formed under CO2/Ar (Figure S8b), the two peaks shifted toward lower frequency by about 10 cm–1 and the bridged adsorbed COad peak disappeared, which could be attributed to the electron donation of Had on the Ru surface. (29) On switching off the plasma, the CH4 concentration decreased immediately (Figure S9), while the formyl species decreased slowly (within 4 min), indicating that the system without plasma discharge was inactive for CH4 formation (Figure S9b). The gradual decrease of formyl band (within 4 min) reflects its desorption under the NTP-off condition. CO2 hydrogenation can undergo the formyl pathway over Ru-based catalysts, (30,31) which involves the direct CO2 dissociation to carbonyl (COad) and Oad, followed by the hydrogenation of COad. The subsequent hydrogenation of COad will form the formyl species as the intermediates for CH4 production. As compared with the DRIFTS findings from the thermal system (i.e., only carbonyl species were observed, Figure S7), the appearance of carbonyl species and formyl species under NTP conditions suggested the presence of an alternative reaction pathway (i.e., formyl pathways) for CO2 hydrogenation under NTP. Thus, evolution of the surface species as a function of ToS coupled with the change in CH4 signal intensity (from MS) was correlated, as presented in Figure 3d. The COad species increased at a steeper rate than gas CH4, which could be explained by the plasma-assisted CO2 dissociation in the gas phase and the dissociation of adsorbed CO2 on the catalyst surface. The same phenomenon was found between the formation rates of surface formyl species and CH4, indicating CHxO species originating from reactions between COad and Had and as the surface intermediate for CH4 production. (30,32) The findings of this work confirmed the presence of the formyl pathway in CO2 hydrogenation over Ru/SiO2 under NTP conditions; i.e., CO2 was dissociated to COad and Oad species on the catalyst surface, then COad was hydrogenated with Had into formyl intermediate (CHxO) species, and finally, the formyl group reacted toward CH4 and H2O. In comparison with the thermally activated CO2 hydrogenation, the vibrationally activated CO2 molecules under NTP conditions could adsorb on the catalyst surface with lower energy barriers, which facilitated the formation of COad species. (14) This activation promoted the hydrogenation of CO2 and formation rate of CH4, leading to the reaction order of pCO2 increasing slightly. Additionally, the plasma-induced excited/dissociated H radicals in the gas phase might also interact with the adsorbed species to form CH4 (i.e., the formyl pathway) via the Eley–Rideal mechanism in CO2 hydrogenation under NTP. (14,25) Due to the relatively low dissociation energy of H2 molecules (∼4.5 eV), (33) the plasma could activate H2 more efficiently, which produces more H radicals with an increase in H2 concentration in the feed. Therefore, under NTP, the H2 partial pressure has a significant influence on the formation rate of CH4, leading to a much higher reaction order with respect to pH2 than that in the thermal catalysis.
Figure 3
Figure 3. In situ DRIFTS spectra of surface species for CO2 hydrogenation over the Ru/SiO2 catalyst under (a) the NTP-off condition with the feed gas of 3% CO2 + 9% H2 + Ar, (b) NTP-on condition with the feed gas (at 5.5 kV and 27.0 kHz), and (c) NTP-off condition with the feed gas. (d) Relative intensities of surface species as a function of time-on-stream recorded by in situ DRIFTS from (b) and relative intensity change of methane recorded in MS (Figure S9) during CO2 hydrogenation by NTP activation (at 5.5 kV and 27.0 kHz).
3.3. Investigation of CO Poisoning on CO2 Hydrogenation
Catalyst deactivation is complex and significant for practical catalysis. As expected, under the NTP condition (at 6.5 kV, 21.0 kHz), the Ru/SiO2 catalyst in CO2 hydrogenation presented excellent stability over 27 h ToS with CO2 conversions and CH4 selectivity maintained at 64.7 ± 0.7% and 94.1 ± 0.3%, respectively (Figure S10). Comparative TEM analysis of the catalyst before and after the longevity test showed no significant change regarding the particle sizes, neither the sign of metal sintering, which confirmed the anticoking and antisintering performance of the NTP-catalysis (Figure S11).
In addition to coking and sintering, catalyst poisoning is another major factor to deactivate the catalyst. Accordingly, to understand CO poisoning in the catalysis under the thermal and plasma conditions, relevant experiments were performed by varying CO concentration in the gas feed, keeping the H2/C (i.e., CO2 + CO) inlet molar ratio constant. Figure 4 shows the thermal and NTP-activated carbon conversions (CO2, CO, and overall) as a function of ToS with different CO/CO2 ratios in the feed gas. Under the thermal condition at 330 °C (Figure 4a), the fresh Ru/SiO2 catalyst showed a stable CO2 conversion (∼47%) without CO in the feed gas (CO/CO2 = 0, ToS = 0–70 min in Figure 4a). When CO (CO/CO2 = 0.25) was introduced in the gas mixture, CO2 conversion decreased to 35%, while CO was almost completely consumed, promoting the overall carbon conversion and CH4 production due to CO hydrogenation. By switching back to the “CO-free” feed gas (CO/CO2 = 0, ToS = 165–240 min in Figure 4a), catalyst deactivation occurred, and the catalyst could not be fully recovered, as evidenced by the reduced CO2 conversion (Figure 4a) and CH4 production (Figure S12a), in comparison with that of the fresh catalyst. By further increasing the CO/CO2 ratio to 0.5 and 1.0, the decrease in CO2 conversion and deactivation of catalyst became more significant, while the CO conversion remained almost complete. The findings showed a strong inhibiting effect of CO on CO2 conversion. The condition with CO/CO2 = 0.25 in the feed gas (ToS = 590–680 min in Figure 4a) was tested again, and carbon conversion and CH4 production were lower than the previously measured values, suggesting the permanent deactivation of Ru/SiO2. By adding more CO in the feed (i.e., CO/CO2 ratio of 2), severe CO poisoning was measured. Specifically, the CO2 conversion dropped rapidly below zero, suggesting that CO2 was formed in the system. This might be attributed to the presence of CO disproportionation (2CO → C + CO2) (34) and/or water-gas shift reaction (WGSR, CO + H2O → H2 + CO2) (35) due to the excessive CO in the feed and strong adsorption of CO on the Ru surface. Accordingly, in the thermal catalysis system, a decrease in CO2 conversion with CO cofeeding was not due to the kinetic effect, that is, the diluted CO2 concentration in the gas feed, as discussed above (Figure 2). With the presence of CO in the feed, competitive adsorption of CO and CO2 on metal active sites occurs. (36) Since the adsorption energy of CO (−2.3 eV) is much lower than that of CO2 (−0.52 eV), (37) preferential adsorption of CO and inhibited CO2 adsorption on the Ru surface are expected and, thus, a decrease in CO2 conversion. It was proposed that the formation of strongly adsorbed carbonyl species (11,38) due to the presence of CO might be the dominant factor for catalyst deactivation. Therefore, the mechanism of CO poisoning of the Ru/SiO2 catalyst was investigated by in situ DRIFTS analysis (to be discussed later).
Figure 4
Figure 4. CO2, CO, and carbon conversions as a function of ToS in CO poisoning experiments with different CO/CO2 inlet molar ratios under (a) thermal condition (at 330 °C) and (b) NTP condition (at 6.5 kV and 21.0 kHz).
As shown in Figure 4b, under the NTP condition at 13.0 kV, 54% CO2 conversion over the Ru/SiO2 catalyst was measured with the absence of CO in the feed (i.e., CO/CO2 = 0, ToS = 0–70 min, in Figure 4b). By introducing CO in the feed (with CO/CO2 = 0.25), CO2 conversion decreased slightly to ∼49%, and CO conversion was measured at about 70%, being lower than that under the thermal condition (which was close to 100%). By increasing the CO concentration in the feed gas (i.e., CO/CO2 = 0.5, 1.0 and 2.0, respectively), a decrease in CO2 conversions was measured (due to the change of gas composition); however, catalyst deactivation was insignificant since the carbon conversion remained stable in stream during the cofeeding tests. More importantly, the catalyst activity regarding CO2 conversion and CH4 production in CO2 hydrogenation can be totally recovered when the system was switched back to the CO-free feed, regardless of the previous CO concentration in the feed, confirming that (i) NTP could be able to completely regenerate the catalyst and (ii) NTP is able to mitigate CO poisoning on CO2 hydrogenation (Figure S12b). Interestingly, under NTP conditions, in comparison with ∼100% CO conversions under the thermal condition, CO conversions increased from 70 to 92% with an increase in the inlet CO/CO2 ratio from 0.25 to 2. This suggested that the reasons for the decrease in CO2 conversion in both systems may be different. As discussed above, in thermal catalysis, preferred CO adsorption on the Ru surface and the subsequent CO hydrogenation prevailed, causing the reduction of the CO2 conversion and almost 100% CO conversion. Conversely, under NTP conditions, the plasma could activate the CO2 molecules in the gas phase and the vibrationally excited CO2 could adsorb on the catalyst surface with lower energy barriers, which facilitated the adsorption of CO2 on the catalyst surface. (14) Additionally, the collision of reactive plasma species (such as the vibrationally excited CO2 and the excited state of CO, H, OH, and CH in the gas phase according to OES and FTIR (9,25,39)) might help remove the strongly adsorbed surface COad and then release the active sites for adsorption. (14,40,41) Thus, NTP alleviated CO adsorption and facilitated CO2 adsorption, which result in lower CO conversions and higher CO2 conversions than those in the thermal catalysis.
The superiority of the NTP-catalysis over the thermal counterpart, regarding the maintenance and regeneration of the catalyst activity, was proved by the long-term CO poisoning study in Figure 5. At 330 °C, the deterioration of the catalyst performance with the presence of CO in the feed was evident during the 9 h test. Specifically, CO2 and CO conversions (Figure 5a) and CH4 formation (Figure S13a) dropped by about 42, 7, and 15%, respectively. By removing CO from the feed (ToS = 640–790 min in Figure 5a), CO2 conversion and CH4 production over Ru/SiO2 were recovered to ∼93 and ∼87% only. Considering that flowing inert gases at high temperature could be used to recover the catalyst reactivity, the deactivated catalyst was regenerated in situ at 330 °C by sweeping with Ar for 3.5 h, trying to remove the strongly adsorbed surface species from the catalyst surface. However, as shown in Figure 5a and Figure S13a, the deactivation of catalyst due to CO poisoning under the thermal condition was permanent. Previous theoretical and experimental studies (42,43) suggested that the CO molecule could block the active sites for CO2 and H2 adsorption, thus decreasing the dissociated Had on the Ru surface and consequently leading to the deposition of surface carbon species and metal sintering. Conversely, in NTP-catalysis (at 6.5 kV), the catalyst presented stable performance over 9 h, with the constant CO2 conversion at about 38% and decreased CO conversion (by about 6%). Furthermore, after returning to the CO-free feed (ToS = 640–790 min, Figure 5b), the CO2 conversion was recovered to ∼53% slowly (being comparable with that of the fresh catalyst at ToS = 0–100 min). During the same period (ToS = 640–790 min in Figure S13b), the corresponding CH4 production decreased to the initial level, confirming that NTP could recover the performance of the catalyst. The recovery trend of CO2 conversion and CH4 production was attributed to the consumption of residual adsorbed carbon species under NTP, thus regenerating active sites available for CO2 hydrogenation. The catalyst was further treated in situ under Ar and NTP (at 4.0 kV) for 30 min (ToS = 790–820 min, as shown in Figure 5b). After that, NTP-activated CO2 hydrogenation was performed again with the CO-free feed (ToS = 829–945 min in Figure 5b), and the NTP-catalysis system showed the fully recovered performance. The corresponding TEM analysis of the catalysts after the long-term deactivation test (Figure S14) showed the metal sintering of the catalyst in thermal catalysis; that is, the Ru particle size increased from ∼1.6 to ∼3.1 nm after the thermal catalysis. Conversely, the Ru particle size showed no significant changes after the NTP-catalysis, confirming the antisintering ability of the hybrid system.
Figure 5
Figure 5. Long-term deactivation test with the CO2/CO/H2 mixtures, regeneration treatment under Ar, and catalysis in CO2/H2 over the Ru/SiO2 catalyst under (a) the thermal condition (at 330 °C) and (b) NTP condition (at 6.5 kV and 21.0 kHz). Experimental conditions: feed gas composition of H2/C = 3, CO/CO2 = 0.5, and WHSV of 30,000 mL (STP) gcat–1 h–1.
3.4. Mechanisms of CO Poisoning
To understand CO poisoning in the catalysis, comparative in situ DRIFTS–MS studies were carried out and compared with the DRIFTS study of CO2 hydrogenation in Figure 3 and Figure S7. Under the thermal condition, the DRIFTS spectra measured with CO/H2 mixture (Figure 6a,c) showed that the intensity of the carbonyl bands was significantly enhanced compared with the case of CO2 hydrogenation (Figure S7), suggesting the relatively strong CO binding with the Ru surface. Specifically, in addition to the gas-phase CO band (at ∼2143 cm–1), the broad carbonyl bands in a range of 2140–1770 cm–1 can be deconvoluted into three kinds of COad bonds, i.e., the bands at 1775 and 1950–1980 cm–1 (for the bridged carbonyls), 2005 cm–1 (for the linearly adsorbed CO with monobinding configuration), and 2030–2075 cm–1 (for the linearly adsorbed CO with multiple-binding configuration). (30) After changing the feed to inert Ar (Figure 6b,c), the COad bands decreased much slower than that in CO2 hydrogenation (Figure S7b), indicating that more strongly adsorbed carbonyl species formed on the surface when CO was in the feed. By switching the feed to H2 (Figure 6e,f), surface carbonyl species disappeared within 10 min, and the CH4 concentration at the outlet of the DRIFTS cell showed a maximum (at ∼1.3 min, which was followed by a continuous decline until zero), showing that the adsorbed CO was converted to CH4 in the presence of H2. The evolution of the respective surface species as a function of time (Figure 6f) showed that the intensity of the carbonyl group at 2030–2050 cm–1 quickly decayed (within 2 min) under H2, being the most reactive surface species, while the bridged carbonyl at 1775 cm–1 and linear monocarbonyl at 2005 cm–1 disappeared completely with comparatively slow rates. In contrast, the intensity of the peak at 1950–1980 cm–1, corresponding to geminal dicarbonyls adsorbed on the low coordination Ru sites, remained constant within the initial 2 min and then decreased slowly, being relatively stable on the Ru surface and less reactive for hydrogenation. (44) The presence of these stable and less reactive surface species might block the active sites and hence contributed to the catalyst deactivation. Based on the findings from in situ DRIFTS–MS, one can conclude that, under the thermal condition, CO hydrogenation proceeded with similar pathways to those of the catalytic CO2 hydrogenation. (45) However, the strong adsorption of CO on the catalyst surface could saturate the active sites, inhibiting CO2 and H2 adsorption.
Figure 6
Figure 6. In situ DRIFTS spectra of surface species collected at 250 °C in the thermally activated CO hydrogenation over the Ru/SiO2 catalyst. (a) Initial feed composition: 3% CO + 9% H2+ Ar; (b) change to inert Ar; (c) variations of COad intensity from in situ DRIFTS and CH4 intensity from MS after switching to Ar at 250 °C; (d) change back to the feed: 3% CO + 9% H2 + Ar; (e) change to H2/Ar; (f) variations of COad intensity from in situ DRIFTS and CH4 intensity from MS after switching the feed to H2/Ar at 250 °C.
With the CO2 + CO + H2 feed under the thermal condition, the associated DRIFTS spectra showed the combined features of the CO2-/CO-alone hydrogenation system (as shown in Figure S15a,c), which was substantiated by the presence of strongly adsorbed COad and CxHy species on the surface. After the introduction of CO into the feed, CO coverage increased significantly and could not be completely removed by Ar sweeping (Figure S15d), indicating that the strongly adsorbed COad occupied the active sites for CO2 and H2 adsorption. Accordingly, based on the findings obtained from the thermal catalysis and relevant in situ DRIFTS characterization, it was plausible that the presence of CO in the system produced strongly adsorbed CO species on the Ru sites, which inhibited both CO2 and H2 adsorption, thus suppressing CO2 hydrogenation. Due to the limited concentration of surface Had species, the relatively stable and inactive carbon-containing species, such as carbonyl deposition, were encouraged to be formed on the catalyst surface, and they might progressively block the active sites. Thus, the associated carbonaceous species deposition and metal sintering lead to the permanent catalyst deactivation, (46) which confirms the results in Figures 4a and 5a.
Without plasma discharge at RT, the Ru/SiO2 catalyst showed no activity for CO hydrogenation, that is, (i) no CO conversion by MS as shown in Figure 7a and (ii) the only presence of gas-phase CO (at ∼2143 cm–1) according to DRIFTS (Figure 7b). Upon the ignition of NTP, the MS profiles (Figure 7a) showed the instant decrease of CO signal and simultaneous increase of CO2 and CH4 signals, confirming the production of CH4 and CO2 in the NTP-catalysis. CO2 formation was due to WGSR, which could be activated by NTP. (5) Water was the product from the NTP-activated catalytic CO hydrogenation. As discussed above (Figure 4b), when CO was introduced into the feed for NTP-activated CO2 hydrogenation, a decrease in CO2 conversion was measured, which might be partly caused by the water-gas shift reaction. Simultaneously, the gas-phase CO2 peak at about 2350 cm–1 was measured by DRIFTS (Figure 7c), in line with the intensity change from MS. In the OCO region (Figure 7c,d), the peak for gas-phase CO at 2143 cm–1 disappeared, and the continuous development of the IR bands at 2095 and 2160 cm–1 could be attributed to the linearly adsorbed carbonyl species on Ruδ+ with Ruδ+-CO and Ruδ+-(CO)n configurations, respectively. Another characteristic peak at 2040 cm–1 was assigned to the CO linearly adsorbed on Ru0, while the gradually increased peaks at about 1272 and 1306 cm–1 corresponded to formyl species (CHxO). The evolution of the surface carbon species recorded by DRIFTS as a function of time is correlated (Figure 7f). The increasing rate of carbonyl bands at 2095 and 2160 cm–1 was comparable with that of formyl species, which supported the fact that CO is the intermediate toward formyl species. Also, the formation rate of COad band at 2040 cm–1 increased relatively fast, which might be due to CO2 dissociation (formed by water-gas shift reaction) and CO adsorption. By switching off NTP, the peak of the gas-phase CO2 decreased quickly, and the system was not active again for CO hydrogenation, which was in good agreement with the MS profile. Regarding the carbon species, the formyl species disappeared gradually due to desorption after the extinction of plasma (Figure S16), while COad band intensity barely changed, indicating the strong interaction between the COad species and catalyst surface. Furthermore, when the feed was switched to H2/Ar (from 3% CO + 9% H2 + Ar), DRIFTS characterization (Figure S17a) showed that the surface COad species at 2090 cm–1 (due to gas-phase CO adsorption) decreased immediately, while the intensity of formyl species increased initially and then decreased slowly. The initial increase of the formyl species on the catalyst surface could be ascribed to the reaction between COad and Had (to form the formyl), while the subsequent decrease of the formyl species was due to the consumption of residual formyl species to form CH4. As shown in Figure S17b, the rate of decrease of formyl species and CH4 concentration (at the outlet of the DRIFTS cell by MS) was similar, confirming that the formyl species originated from the reaction between COad and Had and were the active intermediate for CH4 formation. DRIFTS analysis of CO hydrogenation under the NTP condition showed that CO hydrogenation to CH4 proceeded via CO adsorption and the formyl pathway, being similar with that of CO2 hydrogenation (Figure 3).
Figure 7
Figure 7. (a) Corresponding MS signals collected simultaneously from the DRIFTS cell as a function of time during the NTP-assisted CO hydrogenation over the Ru/SiO2 catalyst. In situ DRIFTS spectra of surface species for CO hydrogenation over the Ru/SiO2 catalyst under (b) the NTP-off condition with the feed gas of 3% CO + 9% H2 + Ar, (c, d) NTP-on condition with the feed gas (at 5.5 kV and 27.0 kHz), and (e) NTP-off condition with the feed gas. (f) Relative intensities of surface species as a function of ToS recorded in the in situ DRIFTS from (c) and (d) during CO hydrogenation under NTP (at 5.5 kV and 27.0 kHz).
NTP-catalysis with the CO2/CO/H2 feed was examined by DRIFTS–MS (Figure 8 and Figure S18). Being different from CO hydrogenation, the COad peak at 2080 cm–1, due to CO2 dissociation, appeared first and then combined with the peak at 2097 cm–1 (originating from the gas-phase CO adsorption). Accordingly, the evolution profile of the surface carbon species (Figure 8c) showed that the COad species had higher increasing rates than that of formyl species initially (within 8 min) due to CO2 dissociation and CO adsorption on the Ru sites. The subsequent change in the increasing rate was due to saturation of relevant active sites on the Ru surface by CO2/CO adsorption. (30) This finding suggested that CO2 and CO coadsorption existed in the NTP-catalysis. In contrast, the formyl species presented a constant formation rate, confirming that the formyl species originated from the reaction between COad and Had. In addition, by switching CO feed on and off alternatively, DRIFTS–MS characterization of the catalysis (Figure S19) showed that the CO2 MS signal increased with CO in the feed (i.e., production of CO2), which confirms the presence of WGSR under the NTP condition with the CO2/CO/H2 mixture. Therefore, under NTP conditions, the presence of CO in the feed affected CO2 conversions, which was due to (i) the occurrence of WGSR in the system for CO2 formation and (ii) the relatively strong adsorption of CO, in line with the result in Figure 4b. Based on the in situ DRIFTS characterization and relevant discussion, the presence of CO in the feed did not alter the reaction pathways for CO2 hydrogenation under thermal and NTP conditions. However, in comparison with the CO poisoning under the thermal conditions (as discussed before, i.e., due to strong CO adsorption and associated metal sintering of the catalyst), the collisions between reactive plasma-derived species in NTP could recover the active sites by removing the adsorbed carbon species effectively, which lead to the sites available for CO2 adsorption. (40,41,47) This is confirmed by the comparison of the relevant IR spectra (Figure S20), which showed the comparatively low intensity of the adsorbed COad on the Ru catalyst under NTP. Therefore, NTP-catalysis promoted the adsorption of CO2 and alleviated CO adsorption on the catalyst surface in the presence of CO, mitigating the CO poisoning effect on the performance of CO2 hydrogenation and being opposite to that experienced by the thermal catalysis. More importantly, according to the literature, (48−50) H2O molecules will occupy the active sites and present an inhibiting effect on the CO2 hydrogenation. Conversely, NTP enabled WGSR of CO with the produced H2O, which shifted the equilibrium of CO2 hydrogenation toward CH4 production. The phenomenon observed in the system under investigation showed the interesting effect of CO on NTP-catalytic CO2 hydrogenation, that is, as a reaction promoter rather than a catalyst poison, due to the copresence of WGSR, CO2 hydrogenation, and CO hydrogenation under NTP conditions.
Figure 8
Figure 8. In situ DRIFTS spectra of surface species for hydrogenation of CO2/CO over the Ru/SiO2 catalyst under (a, b) the NTP-on condition with the feed gas of 1.5% CO2 + 1.5% CO + 9% H2 + Ar (at 5.5 kV and 27.0 kHz), (c) relative intensities of surface species as a function of ToS recorded in the in situ DRIFTS from (a) and (b), and (d) NTP-off condition with the feed gas.
4. Conclusions
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In this study, the NTP-catalysis system was demonstrated to be efficient for CO2 hydrogenations under atmospheric conditions, in which 65% CO2 conversion and 63% CH4 yield can be achieved over the Ru/SiO2 catalyst. Also, the intrinsic nature of catalyst such as surface area is crucial under both thermal and NTP conditions. The comparative kinetic and in situ DRIFTS–MS study revealed that the NTP-catalysis could lower the energy barrier required for catalysis and enable both Langmuir–Hinshelwood and Eley–Rideal mechanisms.
The effect of CO on the catalysis under both thermal and NTP conditions was investigated to understand CO poisoning comparatively. In the thermal catalysis, the catalyst suffered from a significant decrease in CO2 conversion and deactivation due to CO poisoning, while in the NTP-catalysis, the CO played a different role in the system, and the catalyst showed comparatively good stability and regenerability by NTP. In situ DRIFTS–MS study of the thermal catalysis showed that (i) CO preferred to adsorb on the Ru surface strongly to inhibit CO2 and H2 adsorption and decrease CO2 conversion significantly and (ii) the formation of less reactive and strongly adsorbed carbon species (e.g., COad) due to CO strong adsorption and metal sintering deactivates the catalyst permanently. Conversely, in NTP-catalysis, collisions of reactive plasma-derived species contributed to the recovery of the active sites by removing the strongly adsorbed COad, which facilitated CO2 adsorption and, hence, CO2 hydrogenation. Therefore, NTP-catalysis could alleviate the CO effect on CO2 hydrogenation and regenerate the catalyst in situ in the presence of CO during the catalysis. Importantly, the NTP-induced WGSR of CO with the produced H2O also promoted the equilibrium shift of CO2 hydrogenation toward CH4 production. This work demonstrates that, under NTP conditions, the role played by CO in Ru-catalyzed CO2 hydrogenation is fundamentally different from its positioning role in thermal catalysis, showing the potential of NTP-catalysis to address some of the challenges in conventional heterogeneous catalysis, specifically, the development of advanced hybrid NTP-catalysis systems to solve the chemical deactivation issues for practical catalysis.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscatal.0c03620.
Detailed characterization of catalysts; relevant catalyst assessment for catalytic CO2 hydrogenation; kinetic parameters of the thermal and NTP systems; relevant in situ DRIFTS data of the thermal and NTP-catalysis systems (PDF)
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Author Information
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- Christopher Hardacre - Department of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom;
http://orcid.org/0000-0001-7256-6765;
- Xiaolei Fan - Department of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom;http://orcid.org/0000-0002-9039-6736;
- Shaojun Xu - UK Catalysis Hub, Research Complex at Harwell, Didcot OX11 0FA, United Kingdom; Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom;http://orcid.org/0000-0002-8026-8714
- Cristina E. Stere - Department of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom;http://orcid.org/0000-0001-8604-0211
- Sihai Yang - Department of Chemistry, School of Natural Science, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom;http://orcid.org/0000-0002-1111-9272
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Acknowledgments
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S.X. thanks the financial support from the Dean’s Doctoral Scholar Awards from the University of Manchester. The UK Catalysis Hub is kindly thanked for resources and support provided via our membership of the UK Catalysis Hub Consortium and funded by EPSRC grant EP/R026939/1, EP/R026815/1, EP/R026645/1, EP/R027129/1, or EP/M013219/1(biocatalysis).
References
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This article references 50 other publications.
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- 3Bogaerts, A.; Tu, X.; Whitehead, J. C.; Centi, G.; Lefferts, L.; Guaitella, O.; Azzolina-Jury, F.; Kim, H.-H.; Murphy, A. B.; Schneider, W. F.; Nozaki, T.; Hicks, J. C.; Rousseau, A.; Thevenet, F.; Khacef, A.; Carreon, M. The 2020 Plasma Catalysis Roadmap. J. Phys. D: Appl. Phys. 2020, 53, 443001, DOI: 10.1088/1361-6463/ab9048Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvV2hurzL&md5=d6d567f273f525184ef3c93f312ec55bThe 2020 plasma catalysis roadmapBogaerts, Annemie; Tu, Xin; Whitehead, J. Christopher; Centi, Gabriele; Lefferts, Leon; Guaitella, Olivier; Azzolina-Jury, Federico; Kim, Hyun-Ha; Murphy, Anthony B.; Schneider, William F.; Nozaki, Tomohiro; Hicks, Jason C.; Rousseau, Antoine; Thevenet, Frederic; Khacef, Ahmed; Carreon, MariaJournal of Physics D: Applied Physics (2020), 53 (44), 443001CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)A review. Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chems. and fuels, CH4 activation into hydrogen, higher hydrocarbons or oxygenates, and NH3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile org. compd. remediation, particulate matter and NOx removal. In addn., plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over 'conventional' catalysis, as outlined in the Introduction. However, a better insight into the underlying phys. and chem. processes is crucial. This can be obtained by expts. applying diagnostics, studying both the chem. processes at the catalyst surface and the physicochem. mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technol. needed to meet these challenges.
- 4Vakili, R.; Gholami, R.; Stere, C. E.; Chansai, S.; Chen, H.; Holmes, S. M.; Jiao, Y.; Hardacre, C.; Fan, X. Plasma-Assisted Catalytic Dry Reforming of Methane (DRM) over Metal-Organic Frameworks (MOFs)-Based Catalysts. Appl. Catal., B 2020, 260, 118195, DOI: 10.1016/j.apcatb.2019.118195Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvVWiur7E&md5=9dff32f0db929667e743f170edc03d18Plasma-assisted catalytic dry reforming of methane (DRM) over metal-organic frameworks (MOFs)-based catalystsVakili, Reza; Gholami, Rahman; Stere, Cristina E.; Chansai, Sarayute; Chen, Huanhao; Holmes, Stuart M.; Jiao, Yilai; Hardacre, Christopher; Fan, XiaoleiApplied Catalysis, B: Environmental (2020), 260 (), 118195CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Plasma-assisted dry reforming of methane (DRM) was performed in a dielec. barrier discharge (DBD) reactor. The effect of different packing materials including ZrO2, UiO-67 MOF and PtNP@UiO-67 on plasma discharge was investigated, showing that ZrO2 suppressed the plasma generation while UiO-67 improves it due to its porous nature which favors the formation of filamentary microdischarges and surface discharges. The improved plasma discharge increased the conversion of CH4 and CO2 by about 18% and 10%, resp., compared to the plasma-alone mode. In addn., the distribution of hydrocarbon products changed from dominant C2H6 in the plasma-alone mode to C2H2 and C2H4 in the UiO-67 promoted plasma-assisted DRM. The UiO-67 MOF was stable in plasma, showing no significant changes in its properties under different treatment times, discharge powers and gases. Pt nanoparticles (NPs) on UiO-67 improved plasma-assisted DRM, esp. the selectivity due to the presence of surface reactions. Due to the dehydrogenation of hydrocarbons over Pt NPs, the selectivity to hydrocarbons decreased by 30%, compared to the UiO-67 packing. In situ diffuse reflectance IR Fourier transformed spectroscopy (DRIFTS) was carried out to probe the surface reactions on PtNP@UiO-67 catalyst, showing the decompn. of surface formats to CO and C2H4 dehydrogenation over the metallic Pt. The PtNP@UiO-67 catalyst showed good reusability in the plasma-assisted DRM, and H2 prodn. was improved by high CH4/CO2 molar ratio and low feed flow rate.
- 5Stere, C. E.; Anderson, J. A.; Chansai, S.; Delgado, J. J.; Goguet, A.; Graham, W. G.; Hardacre, C.; Taylor, S. F. R.; Tu, X.; Wang, Z.; Yang, H. Non-Thermal Plasma Activation of Gold-Based Catalysts for Low-Temperature Water-Gas Shift Catalysis. Angew. Chem., Int. Ed. 2017, 56, 5579– 5583, DOI: 10.1002/anie.201612370Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmtVels74%253D&md5=0866dd49e5db42a6ec8e9766dc96cbd7Non-Thermal Plasma Activation of Gold-Based Catalysts for Low-Temperature Water-Gas Shift CatalysisStere, Cristina E.; Anderson, James A.; Chansai, Sarayute; Delgado, Juan Jose; Goguet, Alexandre; Graham, Willam G.; Hardacre, C.; Taylor, S. F. Rebecca; Tu, Xin; Wang, Ziyun; Yang, HuiAngewandte Chemie, International Edition (2017), 56 (20), 5579-5583CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Non-thermal plasma activation has been used to enable low-temp. water-gas shift over a Au/CeZrO4 catalyst. The activity obtained was comparable with that attained by heating the catalyst to 180 °C providing an opportunity for the hydrogen prodn. to be obtained under conditions where the thermodn. limitations are minimal. Using in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS), structural changes assocd. with the gold nanoparticles in the catalyst have been obsd. which are not found under thermal activation indicating a weakening of the Au-CO bond and a change in the mechanism of deactivation.
- 6Xu, S.; Chansai, S.; Stere, C.; Inceesungvorn, B.; Goguet, A.; Wangkawong, K.; Taylor, S. F. R.; Al-Janabi, N.; Hardacre, C.; Martin, P. A.; Fan, X. Sustaining Metal–Organic Frameworks for Water-Gas Shift Catalysis by Non-Thermal Plasma. Nat. Catal. 2019, 2, 142– 148, DOI: 10.1038/s41929-018-0206-2Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGisb7P&md5=c93a4af37296622e4d5a7c96eaa5af93Sustaining metal-organic frameworks for water-gas shift catalysis by non-thermal plasmaXu, Shaojun; Chansai, Sarayute; Stere, Cristina; Inceesungvorn, Burapat; Goguet, Alexandre; Wangkawong, Kanlayawat; Taylor, S. F. Rebecca; Al-Janabi, Nadeen; Hardacre, Christopher; Martin, Philip A.; Fan, XiaoleiNature Catalysis (2019), 2 (2), 142-148CODEN: NCAACP; ISSN:2520-1158. (Nature Research)The limited thermal and water stability of metal-org. frameworks (MOFs) often restricts their applications in conventional catalysis that involve thermal treatment and/or use of water. Non-thermal plasma (NTP) is a promising technique that can overcome barriers in conventional catalysis. Here we report an example of an NTP-activated water-gas shift reaction (WGSR) over a MOF (HKUST-1). Significantly, the exceptional stability of HKUST-1 was sustained under NTP activation and in the presence of water, which led to a high specific rate of 8.8 h-1. We found that NTP-induced water dissocn. has a twofold promotion effect in WGSR, as it facilitates WGSR by supplying OH and sustains the stability and hence activity of HKUST-1. In situ characterization of HKUST-1 revealed the crit. role of open Cu sites in the binding of substrate mols. This study paves the way to utilize MOFs for a wider range of catalysis.
- 7Chen, H.; Mu, Y.; Shao, Y.; Chansai, S.; Xu, S.; Stere, C. E.; Xiang, H.; Zhang, R.; Jiao, Y.; Hardacre, C.; Fan, X. Coupling Non-Thermal Plasma with Ni Catalysts Supported on Beta Zeolite for Catalytic CO2 Methanation. Catal. Sci. Technol. 2019, 9, 4135– 4145, DOI: 10.1039/C9CY00590KGoogle Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlahurzJ&md5=d7b1d829bbeda9fb39041ba4f53d0629Coupling non-thermal plasma with Ni catalysts supported on BETA zeolite for catalytic CO2 methanationChen, Huanhao; Mu, Yibing; Shao, Yan; Chansai, Sarayute; Xu, Shaojun; Stere, Cristina E.; Xiang, Huan; Zhang, Rongxin; Jiao, Yilai; Hardacre, Christopher; Fan, XiaoleiCatalysis Science & Technology (2019), 9 (15), 4135-4145CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)Catalytic carbon dioxide (CO2) methanation is a promising and effective process for CO2 use and the prodn. of CH4 as an alternative to using natural gas. Nonthermal plasma (NTP) activation was proven to be highly effective in overcoming the thermodn. limitation of reactions under mild conditions and intensifying the CO2 hydrogenation process greatly. Herein, the authors present an example of NTP-assisted catalytic CO2 methanation over Ni catalysts (15%) supported on BETA zeolite employing lanthana (La) as the promoter. A NTP-assisted system presents remarkable catalytic performance in catalytic CO2 methanation without an external heat source. Significantly, the use of Na-form BETA zeolite and the addn. of La (i.e. 15Ni-20La/Na-BETA catalyst) resulted in an improvement in CO2 conversions, surpassing the 15Ni/H-BETA catalyst, i.e. a 7-fold increase in the turnover frequency, TOF (1.45 s-1vs. 0.21 s-1), and selectivity towards CH4 (up to ∼97%). The developed catalyst also exhibited excellent stability under NTP conditions, i.e. a stable performance over a 15 h longevity test (with a TOF of 1.44 ± 0.01 s-1). Comparative in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) characterization of the developed catalysts revealed that the introduction of La2O3 to the Ni catalyst provides more surface hydroxyl groups, and hence enhances CO2 methanation. Addnl., by analyzing the surface species over 15Ni-20La/Na-BETA comparatively under thermal and NTP conditions (by in situ DRIFTS anal.), probably both the Langmuir-Hinshelwood and Eley-Rideal mechanisms coexist in the NTP system due to the presence of dissocd. H species in the gas phase. Conversely, for the thermal system, the reaction has to go through reactions between the surface-dissocd. H and carbonate-like adsorbed CO2 via the Langmuir-Hinshelwood mechanism. The current mechanistic understanding of the NTP-activated system paves the way for the exploration of the reaction mechanisms/pathways of NTP-assisted catalytic CO2 methanation.
- 8Kim, J.; Go, D. B.; Hicks, J. C. Synergistic Effects of Plasma-Catalyst Interactions for CH4 Activation. Phys. Chem. Chem. Phys. 2017, 19, 13010– 13021, DOI: 10.1039/C7CP01322AGoogle Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmvVSiur4%253D&md5=cbc20ae16d132403e3ec0f5ec30fc3e0Synergistic effects of plasma-catalyst interactions for CH4 activationKim, Jongsik; Go, David B.; Hicks, Jason C.Physical Chemistry Chemical Physics (2017), 19 (20), 13010-13021CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The elucidation of catalyst surface-plasma interactions is a challenging endeavor and therefore requires thorough and rigorous assessment of the reaction dynamics on the catalyst in the plasma environment. The first step in quantifying and defining catalyst-plasma interactions is a detailed kinetic study that can be used to verify appropriate reaction conditions for comparison and to discover any unexpected behavior of plasma-assisted reactions that might prevent direct comparison. In this paper, we provide a kinetic evaluation of CH4 activation in a dielec. barrier discharge plasma in order to quantify plasma-catalyst interactions via kinetic parameters. The dry reforming of CH4 with CO2 was studied as a model reaction using Ni supported on γ-Al2O3 at temps. of 790-890 K under atm. pressure, where the partial pressures of CH4 (or CO2) were varied over a range of ≤25.3 kPa. Reaction performance was monitored by varying gas hourly space velocity, plasma power, bulk gas temp., and reactant concn. After correcting for gas-phase plasma reactions, a linear relationship was obsd. in the log of the measured rate const. with respect to reciprocal power (1/power). Although thermal catalysis displays typical Arrhenius behavior for this reaction, plasma-assisted catalysis occurs from a complex mixt. of sources and shows non-Arrhenius behavior. However, an energy barrier was obtained from the relationship between the reaction rate const. and input power to exhibit ≤∼20 kJ mol-1 (compared to ∼70 kJ mol-1 for thermal catalysis). Of addnl. importance, the energy barriers measured during plasma-assisted catalysis were relatively consistent with respect to variations in total flow rates, types of diluent, or bulk reaction temp. These exptl. results suggest that plasma-generated vibrationally-excited CH4 favorably interacts with Ni sites at elevated temps., which helps reduce the energy barrier required to activate CH4 and enhance CH4 reforming rates.
- 9Xu, S.; Chansai, S.; Shao, Y.; Xu, S.; Wang, Y.-c.; Haigh, S.; Mu, Y.; Jiao, Y.; Stere, C. E.; Chen, H.; Fan, X.; Hardacre, C. Mechanistic Study of Non-Thermal Plasma Assisted CO2 Hydrogenation over Ru Supported on MgAl Layered Double Hydroxide. Appl. Catal., B 2020, 268, 118752, DOI: 10.1016/j.apcatb.2020.118752Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjtlartrs%253D&md5=97f29ffdda1fc83436a5c90ba25bc86cMechanistic study of non-thermal plasma assisted CO2 hydrogenation over Ru supported on MgAl layered double hydroxideXu, Shanshan; Chansai, Sarayute; Shao, Yan; Xu, Shaojun; Wang, Yi-chi; Haigh, Sarah; Mu, Yibing; Jiao, Yilai; Stere, Cristina E.; Chen, Huanhao; Fan, Xiaolei; Hardacre, ChristopherApplied Catalysis, B: Environmental (2020), 268 (), 118752CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Carbon dioxide (CO2) hydrogenation to value-added mols. is an attractive way to reduce CO2 emission via upgrading. Herein, non-thermal plasma (NTP) activated CO2 hydrogenation over Ru/MgAl layered double hydroxide (LDH) catalysts was performed. The catalysis under the NTP conditions enabled significantly higher CO2 conversions (∼85%) and CH4 yield (∼84%) at relatively low temps. compared with the conventional thermally activated catalysis. Regarding the catalyst prepn., it was found that the redn. temp. can affect the chem. state of the metal and metal-support interaction significantly, and thus altering the activity of the catalysts in NTP-driven catalytic CO2 hydrogenation. A kinetic study revealed that the NTP-catalysis has a lower activation energy (at ∼21 kJ mol-1) than that of the thermal catalysis (ca. 82 kJ mol-1), due to the alternative pathways enabled by NTP, which was confirmed by the comparative in situ diffuse reflectance IR Fourier (DRIFTS) coupled with mass spectrometry (MS) characterization of the catalytic systems.
- 10Chen, H.; Goodarzi, F.; Mu, Y.; Chansai, S.; Mielby, J. J.; Mao, B.; Sooknoi, T.; Hardacre, C.; Kegnæs, S.; Fan, X. Effect of Metal Dispersion and Support Structure of Ni/Silicalite-1 Catalysts on Non-Thermal Plasma (NTP) Activated CO2 Hydrogenation. Appl. Catal., B 2020, 272, 119013, DOI: 10.1016/j.apcatb.2020.119013Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXotVGjurw%253D&md5=c2e667bbbdfffda1539207671745f59fEffect of metal dispersion and support structure of Ni/silicalite-1 catalysts on non-thermal plasma (NTP) activated CO2 hydrogenationChen, Huanhao; Goodarzi, Farnoosh; Mu, Yibing; Chansai, Sarayute; Mielby, Jerrik Joergen; Mao, Boyang; Sooknoi, Tawan; Hardacre, Christopher; Kegnaes, Soeren; Fan, XiaoleiApplied Catalysis, B: Environmental (2020), 272 (), 119013CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Non-thermal plasma (NTP) activated heterogeneous catalysis is a promising alternative to thermal catalysis for enabling many challenging reactions (e.g. catalytic CO2 hydrogenation) under mild conditions. However, the mechanistic insight into the interaction between highly energetic electrons and vibrationally-excited reactive species with metal catalyst is still lacking. Here, catalytically active Ni nanoparticles supported on silicalite-1 zeolites with different configurations regarding the location of Ni active sites and support pore structures were comparably investigated using catalytic CO2 hydrogenation under the thermal and NTP conditions. Exptl. results revealed that the performance of the NTP-catalysis depends on the configuration of the catalysts significantly. Specifically, catalysts with Ni active sites sit on the outer surface of zeolite crystals (i.e. microporous Ni/S1 and Ni/M-S1@Shell with steam-assisted recrystd. micro-meso-porous structure) showed relatively good catalytic performance at a low applied voltage of 6.0 kV. Conversely, the encapsulated catalyst with hierarchical meso-micro-porous structure (i.e. Ni/D-S1) which has relatively small (i.e. av. Ni particle sizes of 2.8±0.7 nm) and dispersed Ni nanoparticles (i.e. Ni dispersion of ca. 2.5%) demonstrated comparatively the best catalytic performance (i.e. CO2 conversion of ca. 75%) at 7.5 kV. Addnl., under the NTP conditions studied, Ni on carbon-templated mesoporous silicalite-1 (Ni/M-S1) showed the worst selectivity to CH4, which was attributed to the poor accessibility of Ni active sites encapsulated in the enclosed mesopores. This study demonstrated the crucial role of catalyst design in NTP activated catalysis.
- 11Gupta, N. M.; Londhe, V. P.; Kamble, V. S. Gas-Uptake, Methanation, and Microcalorimetric Measurements on the Coadsorption of CO and H2 over Polycrystalline Ru and a Ru/TiO2 Catalyst. J. Catal. 1997, 169, 423– 437, DOI: 10.1006/jcat.1997.1718Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXkslWmsLc%253D&md5=100e787e9c603f85b28fa15cc2f737fcGas-uptake, methanation, and microcalorimetric measurements on the coadsorption of CO and H2 over polycrystalline Ru and a Ru/TiO2 catalystGupta, N. M.; Londhe, V. P.; Kamble, V. S.Journal of Catalysis (1997), 169 (2), 423-437CODEN: JCTLA5; ISSN:0021-9517. (Academic)The adsorption, methanation, and heat evolved over a Ru/TiO2 catalyst were found to be quite different than that over a polycryst. Ru sample, when exposed to CO+H2 (1:4) pulses at different temps. in the range 300-470 K. The coadsorbed H2 is found to have a large promotional effect on the CO uptake by the Ru/TiO2 catalyst, the extent of which depended on the catalyst temp. and the surface coverage. No such effect was obsd. in the case of Ru metal. Thus, while using Ru/TiO2 the ratio H2(ad)/CO(ad) increased progressively from 0.7 to 4 with the rise in catalyst temp. from 300 to 470 K, it was almost const. at ∼5±0.5 in the case of ruthenium metal. The exposure of Ru metal to CO+H2 (1:4) pulses gave rise to a differential heat of adsorption (qd)∼50 kJ mol-1 at all the reaction temps. under study, which corresponded to adsorption of CO and H2 mols. at distinct metal sites and in 1:1 stoichiometry. In the presence of excess H2, a qd value of ∼180-190 kJ mol-1 was obsd. at the reaction temps. above 425 K, suggesting the simultaneous hydrogenation of Cs species formed during CO dissocn. Contrary to this, a qd∼115 kJ mol-1 was obsd. for the CO+H2 (1:4) pulse injection over Ru/TiO2 at 300 K, the value reducing to ∼70 kJ mol-1 at higher reaction temps. Furthermore, a lower qd value (∼50 kJ mol-1) was obsd. during CO adsorption over Ru/TiO2 at 300 K in the presence of excess H2, which increased to ∼250 kJ mol-1 for the sample temps. of 420 and 470 K. These data are consistent with the FTIR spectroscopy results on CO+H2 adsorption over Ru/TiO2 catalyst, showing the formation of Ru(CO)n, RuH(CO)n, and RuH(CO)n-1 type surface complexes (n = 2 or 3) in addn. to the linear or the bridge-bonded CO mols. held at the large metal cluster sites (RuxCO). The relative intensity of IR bands responsible to these species depended on the catalyst temp., the RuxCO species growing progressively with the temp. rise. In the case of Ru metal, the formation of only linearly held surface species is envisaged. Arguments are presented to suggest that the CO mols. adsorbed in the multicarbonyl form require lesser energy to dissoc. and are therefore responsible to the obsd. low temp. (<450 K) methanation activity of Ru/TiO2. On the other hand, the activity at the higher reaction temps., both for the Ru metal and for the Ru/TiO2 catalyst, arises due to dissocn. of the linearly or bridge-bonded CO mols. The Ru-Cn and Ru-C species formed during dissocn. of multicarbonyls and linearly bonded CO, resp., are envisaged to have different rates of graphitization, the former species causing a rapid catalyst deactivation at the lower temps.
- 12Falbo, L.; Visconti, C. G.; Lietti, L.; Szanyi, J. The Effect of CO on CO2 Methanation over Ru/Al2O3 Catalysts: A Combined Steady-State Reactivity and Transient DRIFT Spectroscopy Study. Appl. Catal., B 2019, 256, 117791, DOI: 10.1016/j.apcatb.2019.117791Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGiu7nL&md5=272f5842bc35813fcfab95ea86fe5753The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy studyFalbo, Leonardo; Visconti, Carlo G.; Lietti, Luca; Szanyi, JanosApplied Catalysis, B: Environmental (2019), 256 (), 117791CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)The reactivity of Ru/Al2O3 catalysts in the hydrogenation of CO/CO2 gas stream is investigated in this work to assess the possibility of carrying out CO2 methanation even in the presence of CO in the feed stream. Such a goal is pursued by conducting reactivity studies at process conditions of industrial interest (i.e., at high COx per-pass conversion and with concd. COx/H2 streams) and by monitoring the surface species on the catalyst through transient DRIFTS-MS anal. The catalyst shows gradual deactivation when the methanation is carried out in the presence of CO in the gas feed at low temps. (200-300 °C). However, stable performance is obsd. at higher temps., showing CH4 yields even higher than those obsd. during methanation of a pure CO2 feed. DRIFTS-MS expts. agree with a CO2 methanation pathway where CO2 is adsorbed as bicarbonate on Al2O3 and successively hydrogenated to methane on Ru, passing through formate and carbonyl intermediates. In the presence of CO at low temp., the catalyst shows a higher CO coverage of the Ru sites, a larger formate coverage of the alumina sites and the presence of adsorbed carbonaceous species, identified as carboxylate and hydrocarbon species. By carrying out the CO2 hydrogenation on the deactivated catalyst, carboxylates remain on the surface, effectively blocking CO2 adsorption sites. However, the catalyst deactivation at low temp. is reversible as thermal treatment (>350 °C) is able to restore the catalytic activity. Notably, working above the carboxylate decompn. temp. ensures a clean catalyst surface without high CO coverage, resulting in stable and high performance in CO/CO2 methanation.
- 13Barboun, P.; Mehta, P.; Herrera, F. A.; Go, D. B.; Schneider, W. F.; Hicks, J. C. Distinguishing Plasma Contributions to Catalyst Performance in Plasma-Assisted Ammonia Synthesis. ACS Sustainable Chem. Eng. 2019, 7, 8621– 8630, DOI: 10.1021/acssuschemeng.9b00406Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntlGmu7g%253D&md5=b1b39b8c5db84217b0cf1ada9b614bd7Distinguishing Plasma Contributions to Catalyst Performance in Plasma-Assisted Ammonia SynthesisBarboun, Patrick; Mehta, Prateek; Herrera, Francisco A.; Go, David B.; Schneider, William F.; Hicks, Jason C.ACS Sustainable Chemistry & Engineering (2019), 7 (9), 8621-8630CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Plasma-assisted catalysis is the process of elec. activating gases in the plasma-phase at low temps. and ambient pressure to drive reactions on catalyst surfaces. Plasma-assisted catalytic processes combine conventional heterogeneous surface reactions, homogeneous plasma phase reactions, and coupling between plasma-generated species and the catalyst surface. Herein, we perform kinetically controlled ammonia synthesis measurements in a dielec. barrier discharge (DBD) plasma-assisted catalytic reactor. We decouple contributions due to plasma phase reactions from the overall plasma-assisted catalytic kinetics by performing plasma-only expts. By varying the gas compn., temp., and discharge power, we probe how macroscopic reaction conditions affect plasma-assisted ammonia synthesis on three different γ-alumina-supported transition metal catalysts (Ru, Co, and Ni). Our expts. indicate that the overall reaction and plasma-phase reaction are first-order in both N2 and H2. In contrast, the rate contributions due to plasma-catalyst interactions are first-order in N2 but zeroth order in H2. Furthermore, we find that the tuning of the plasma discharge power is more effective in controlling catalytic performance than the increasing of bulk gas temp. in plasma-assisted ammonia synthesis. Finally, we show that adding a catalyst to the DBD reaction alters the way that productivity scales with the specific energy input (SEI).
- 14Whitehead, J. C. Plasma–Catalysis: The Known Knowns, the Known Unknowns and the Unknown Unknowns. J. Phys. D: Appl. Phys. 2016, 49, 243001, DOI: 10.1088/0022-3727/49/24/243001Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Ort73F&md5=a2e794e822409e646c750b94854d7b87Plasma-catalysis: the known knowns, the known unknowns and the unknown unknownsWhitehead, J. ChristopherJournal of Physics D: Applied Physics (2016), 49 (24), 243001/1-243001/24CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)This review describes the history and development of plasma-assisted catalysis focussing mainly on the use of atm. pressure, non-thermal plasma. It identifies the various interactions between the plasma and the catalyst that can modify and activate the catalytic surface and also describes how the catalyst affects the properties of the discharge. Techniques for in situ diagnostics of species adsorbed onto the surface and present in the gas-phase over a range of timescales are described. The effect of temp. on plasma-catalysis can assist in detg. differences between thermal catalysis and plasma-activated catalysis and focuses on the meaning of temp. in a system involving non-equil. plasma. It can also help to develop an understanding of the gas phase and surface mechanism of the plasma-catalysis at a mol. level. Our current state of knowledge and ignorance is highlighted and future directions suggested.
- 15Gibson, E. K.; Stere, C. E.; Curran-McAteer, B.; Jones, W.; Cibin, G.; Gianolio, D.; Goguet, A.; Wells, P. P.; Catlow, C. R. A.; Collier, P.; Hinde, P.; Hardacre, C. Probing the Role of a Non-Thermal Plasma (NTP) in the Hybrid NTP Catalytic Oxidation of Methane. Angew. Chem., Int. Ed. 2017, 56, 9351– 9355, DOI: 10.1002/anie.201703550Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFegu77J&md5=16ef0b1bf0d349e0b70eff5f0c20a045Probing the Role of a Non-Thermal Plasma (NTP) in the Hybrid NTP Catalytic Oxidation of MethaneGibson, Emma K.; Stere, Cristina E.; Curran-McAteer, Bronagh; Jones, Wilm; Cibin, Giannantonio; Gianolio, Diego; Goguet, Alexandre; Wells, Peter P.; Catlow, C. Richard A.; Collier, Paul; Hinde, Peter; Hardacre, ChristopherAngewandte Chemie, International Edition (2017), 56 (32), 9351-9355CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Three recurring hypotheses are often used to explain the effect of non-thermal plasmas (NTPs) on NTP catalytic hybrid reactions; namely, modification or heating of the catalyst or creation of new reaction pathways by plasma-produced species. NTP-assisted methane (CH4) oxidn. over Pd/Al2O3 was investigated by direct monitoring of the X-ray absorption fine structure of the catalyst, coupled with end-of-pipe mass spectrometry. This in situ study revealed that the catalyst did not undergo any significant structural changes under NTP conditions. However, the NTP did lead to an increase in the temp. of the Pd nanoparticles; although this temp. rise was insufficient to activate the thermal CH4 oxidn. reaction. The contribution of a lower activation barrier alternative reaction pathway involving the formation of CH3(g) from electron impact reactions is proposed.
- 16Mei, D.; Zhu, X.; He, Y.-L.; Yan, J. D.; Tu, X. Plasma-Assisted Conversion of CO2 in a Dielectric Barrier Discharge Reactor: Understanding the Effect of Packing Materials. Plasma Sources Sci. Technol. 2014, 24, 015011 DOI: 10.1088/0963-0252/24/1/015011Google ScholarThere is no corresponding record for this reference.
- 17Mehta, P.; Barboun, P.; Go, D. B.; Hicks, J. C.; Schneider, W. F. Catalysis Enabled by Plasma Activation of Strong Chemical Bonds: A Review. ACS Energy Lett. 2019, 4, 1115– 1133, DOI: 10.1021/acsenergylett.9b00263Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXmslGgur4%253D&md5=c3b7ed533387042051d12feeba67b4e0Catalysis Enabled by Plasma Activation of Strong Chemical Bonds: A ReviewMehta, Prateek; Barboun, Patrick; Go, David B.; Hicks, Jason C.; Schneider, William F.ACS Energy Letters (2019), 4 (5), 1115-1133CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Nonthermal plasma-driven catalysis is an emerging subfield of heterogeneous catalysis that is particularly promising for the chem. transformation of hard-to-activate mols. (e.g., N2, CO2, CH4). In this Review, we illustrate this promise of plasma-enhanced catalysis, focusing on the ammonia synthesis and methane dry reforming reactions, two reactions that have received wide attention and that illustrate the potential for plasma excitations to mitigate kinetic and thermodn. obstacles to chem. conversions. We highlight how plasma activation of reactants can provide access to overall reaction rates, conversions, product yields, and/or product distributions unattainable by thermal catalysis at similar temps. and pressures. Particular emphasis is given to efforts aimed at discerning the underlying mechanisms at play in these systems. We discuss opportunities for and challenges to the advancement of the field.
- 18Zhang, Y.; Wang, H.-y.; Jiang, W.; Bogaerts, A. Two-Dimensional Particle-in Cell/Monte Carlo Simulations of a Packed-Bed Dielectric Barrier Discharge in Air at Atmospheric Pressure. New J. Phys. 2015, 17, 083056 DOI: 10.1088/1367-2630/17/8/083056Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XksFyqsrs%253D&md5=9aac45a820d39f05882942c076e63844Two-dimensional particle-in cell/Monte Carlo simulations of a packed-bed dielectric barrier discharge in air at atmospheric pressureZhang, Ya; Wang, Hong-yu; Jiang, Wei; Bogaerts, AnnemieNew Journal of Physics (2015), 17 (Aug.), 083056/1-083056/12CODEN: NJOPFM; ISSN:1367-2630. (IOP Publishing Ltd.)The plasma behavior in a parallel-plate dielec. barrier discharge (DBD) is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model, comparing for the first time an unpacked (empty)DBD with a packed bed DBD, i.e., a DBD filled with dielec. spheres in the gas gap. The calcns. are performed in air, at atm. pressure. The discharge is powered by a pulse with a voltage amplitude of-20 kV. When comparing the packed and unpacked DBD reactors with the same dielec. barriers, it is clear that the presence of the dielec. packing leads to a transition in discharge behavior from a combination of neg. streamers and unlimited surface streamers on the bottom dielec. surface to a combination of predominant pos. streamers and limited surface discharges on the dielec. surfaces of the beads and plates. Furthermore, in the packed bed DBD, the elec. field is locally enhanced inside the dielec. material, near the contact points between the beads and the plates, and therefore also in the plasma between the packing beads and between a bead and the dielec.-wall, leading to values of 4 × 108 Vm-1, which is much higher than the elec. field in the empty DBD reactor, i.e., in the order of 2 × 107 Vm-1, thus resulting in stronger and faster development of the plasma, and also in a higher electron d. The locally enhanced elec. field and the electron d. in the case of a packed bed DBD are also examd. and discussed for three different dielec. consts., i.e., ∈r = 22 (ZrO2), ∈r = 9 (Al2O3) and ∈r = 4 (SiO2). The enhanced elec. field is stronger and the electron d. is higher for a larger dielec. const., because the dielec. material is more effectively polarized. These simulations are very important, because of the increasing interest in packed bed DBDs for environmental applications.
- 19Zhang, K.; Zhang, G.; Liu, X.; Phan, A. N.; Luo, K. A Study on CO2 Decomposition to CO and O2 by the Combination of Catalysis and Dielectric-Barrier Discharges at Low Temperatures and Ambient Pressure. Ind. Eng. Chem. Res. 2017, 56, 3204– 3216, DOI: 10.1021/acs.iecr.6b04570Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjtlCntrs%253D&md5=c1a4233364eec60381a97cd5cd8a9aabA Study on CO2 Decomposition to CO and O2 by the Combination of Catalysis and Dielectric-Barrier Discharges at Low Temperatures and Ambient PressureZhang, Kui; Zhang, Guangru; Liu, Xiaoteng; Phan, Anh N.; Luo, KunIndustrial & Engineering Chemistry Research (2017), 56 (12), 3204-3216CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)CO2 decompn. to CO and O2 was investigated in a dielec.-barrier discharge (DBD) reactor packed with BaTiO3 balls, glass beads with different sizes, and a mixt. of a Ni/SiO2 catalyst and BaTiO3 balls at lower temps. and ambient pressure. The property of packing beads and the reactor configuration affected the reaction significantly. The Ni/SiO2 catalyst samples were characterized by SEM, XRD, BET, and TEM. The combination of a DBD plasma and a Ni/SiO2 catalyst can enhance CO2 decompn. apparently, and a reaction mechanism of the plasma assisted CO2 dissocn. over the catalyst was proposed. In comparison with the result packed with glass balls (3 mm), the combination of BaTiO3 beads (3 mm) with a stainless steel mesh significantly enhanced the CO2 conversion and energy efficiency by a factor of 14.8, and that with a Ni/SiO2 catalyst by a factor of 11.5 in a DBD plasma at a specific input energy (SIE) of 55.2 kJ/L and low temps. (<115 °C).
- 20Zhang, Y.; Wang, H.-y.; Zhang, Y.-r.; Bogaerts, A. Formation of Microdischarges inside a Mesoporous Catalyst in Dielectric Barrier Discharge Plasmas. Plasma Sources Sci. Technol. 2017, 26, 054002 DOI: 10.1088/1361-6595/aa66beGoogle Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXjvVWqu7k%253D&md5=16c21f12c3fa10189001df4d7ced208fFormation of microdischarges inside a mesoporous catalyst in dielectric barrier discharge plasmasZhang, Ya; Wang, Hong-yu; Zhang, Yu-ru; Bogaerts, AnnemiePlasma Sources Science & Technology (2017), 26 (5), 054002/1-054002/18CODEN: PSTEEU; ISSN:1361-6595. (IOP Publishing Ltd.)The formation process of a microdischarge (MD) in both μm- and nm-sized catalyst pores is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model. A parallel-plate dielec. barrier discharge configuration in filamentary mode is considered in ambient air. The discharge is powered by a high voltage pulse. Our calcns. reveal that a streamer can penetrate into the surface features of a porous catalyst and MDs can be formed inside both μm- and nm-sized pores, yielding ionization inside the pore. For the μm-sized pores, the ionization mainly occurs inside the pore, while for the nm-sized pores the ionization is strongest near and inside the pore. Thus, enhanced discharges near and inside the mesoporous catalyst are obsd. Indeed, the max. values of the elec. field, ionization rate and electron d. occur near and inside the pore. The max. elec. field and electron d. inside the pore first increase when the pore size rises from 4 nm to 10 nm, and then they decrease for the 100 nm pore, due to a more pronounced surface discharge for the smaller pores. However, the ionization rate is highest for the 100 nm pore due to the largest effective ionization region.
- 21Weatherbee, G. D.; Bartholomew, C. H. Hydrogenation of CO2 on Group VIII Metals: II. Kinetics and Mechanism of CO2 Hydrogenation on Nickel. J. Catal. 1982, 77, 460– 472, DOI: 10.1016/0021-9517(82)90186-5Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXjsleqtQ%253D%253D&md5=9119a3bf4f58f7d6b915b03cbc663178Hydrogenation of carbon dioxide on Group VIII metals. II. Kinetics and mechanism of carbon dioxide hydrogenation on nickelWeatherbee, Gordon D.; Bartholomew, Calvin H.Journal of Catalysis (1982), 77 (2), 460-72CODEN: JCTLA5; ISSN:0021-9517.The rate of CO2 hydrogenation on Ni/SiO2 (140 kPa, 500-600 K, 30,000-90,000 h-1) is moderately dependent on CO2 and H concns. at low partial pressures but essentially concn. independent at high partial pressures. Under most typical reaction conditions CO is a reaction product at levels detd. by quasiequil. between surface and gas phase CO. Addn. of CO above this equil. level causes a significant decrease in the rate of CO2 hydrogenation, apparently as a result of product inhibition. Reaction orders and true activation energy are temp. dependent, indicating that a simple power law rate expression is inadequate. Kinetic results are consistent with a complex Langmuir-Hinshelwood mechanism involving dissociative adsorption of CO2 to CO and at. O followed by hydrogenation of CO via a C intermediate of CH4.
- 22Prairie, M. R.; Renken, A.; Highfield, J. G.; Thampi, K. R.; Grätzel, M. A Fourier Transform Infrared Spectroscopic Study of CO2 Methanation on Supported Ruthenium. J. Catal. 1991, 129, 130– 144, DOI: 10.1016/0021-9517(91)90017-XGoogle Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXitVKhu70%253D&md5=3e47d0a327b4aefc080b02561ec3723fFourier transform infrared spectroscopic study of carbon dioxide methanation on supported rutheniumPrairie, Michael R.; Renken, Albert; Highfield, James G.; Thampi, K. Ravindranathan; Graetzel, MichaelJournal of Catalysis (1991), 129 (1), 130-44CODEN: JCTLA5; ISSN:0021-9517.Diffuse-reflectance IR Fourier transform (DRIFT) spectroscopy was used to study in situ, the low-temp. (T <200°) methanation of CO2 over Ru on TiO2 and on Al2O3 supports. For 3.8% Ru/TiO2, the reaction exhibits an activation energy (Ea) of 19 kcal/mol, is 0.43 ± 0.05 order in H2 concn., and essentially independent of CO2 concn. At 110°, 40% of the available metal sites are occupied by CO (θCO = 0.4), a known methanation intermediate. In contrast to Ru/TiO2, Ru/Al2O3, despite having the same Ea and θCO = 0.2, is 15 times less active. Batch catalyst screening expts. showed no dependence of methanation activity on adsorbed CO(COa) formation rate (as modeled by HCOOH dehydration) or on θCO. In view of this, and the fact that CO dissocn. is structure-sensitive, heterogeneity in the active sites is invoked to reconcile the data. The high Ru dispersion on TiO2 is believed to contribute to the enhanced activity over this support. Adsorbed CO2 and H2 react, possibly at the metal-support interface, to form COa via rapid equilibration of the reverse water-gas shift reaction, in which HCOOH (and/or HCOO- ion) play a major role. According to this view, the COa and HCOOa- intermediates seen by FTIR represent accumulated reservoirs en route to CH4, in which the COa hydrogenation step is rate-controlling. An interesting synergy occurs for mixts. of Ru/anatase and Ru/rutile, the former being a better catalyst for COa supply while the latter is more effective in COa hydrogenation.
- 23Solymosi, F.; Erdöhelyi, A.; Kocsis, M. Methanation of CO2 on Supported Ru Catalysts. J. Chem. Soc., Faraday Trans. 1 1981, 77, 1003– 1012, DOI: 10.1039/f19817701003Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXktlWjs7k%253D&md5=6066d7f89255617f89e12e4b43696046Methanation of carbon dioxide on supported ruthenium catalystsSolymosi, Frigyes; Erdohelyi, Andras; Kocsis, MariaJournal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases (1981), 77 (5), 1003-12CODEN: JCFTAR; ISSN:0300-9599.The transformation of C in the form of CO2 into hydrocarbons was studied on supported Ru catalysts. IR spectra showed that chemisorbed CO and [HCO2]- form during the coadsorption of H2 + CO2 at 373 K and during the methanation of CO2 at higher temps. The shift of the CO absorption band to lower frequencies was attributed to the effect of H adsorbed on the same Ru atoms and to surface C formed during the reaction. The [HCO2]- ions form on Ru atoms but migrate rapidly onto the support, thus being inactive in the methanation of CO2. The hydrogenation of CO2 on Ru/Al2O3 occurred at a measurable rate above 443 K yielding almost exclusively CH4. Surface C was detected during the reaction at a level ∼1.5 orders of magnitude less than in the H2 + CO reaction, indicating that the synthesis of CH4 occurs via the formation of surface C and its subsequent hydrogenation.
- 24Kuśmierz, M. Kinetic Study on Carbon Dioxide Hydrogenation over Ru/γ-Al2O3 Catalysts. Catal. Today 2008, 137, 429– 432, DOI: 10.1016/j.cattod.2008.03.003Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXptlygu70%253D&md5=97e2263b31e1e86e39d3fb624ed322e4Kinetic study on carbon dioxide hydrogenation over Ru/γ-Al2O3 catalystsKusmierz, MarcinCatalysis Today (2008), 137 (2-4), 429-432CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Set of Ru/γ-Al2O3 catalysts prepd. by the DIM method was examd. in reaction of carbon dioxide hydrogenation. Overall apparent activation energy reaches a min. at ruthenium dispersion equal 0.5. Reaction order with respect to hydrogen decreases with H/Ru, while reaction order with respect to CO2 changes slightly within examd. dispersion range. Two interpretations of obsd. isokinetic effect, calcd. Tiso and corresponding wavenumber are presented.
- 25Azzolina-Jury, F.; Thibault-Starzyk, F. Mechanism of Low Pressure Plasma-Assisted CO2 Hydrogenation over Ni-USY by Microsecond Time-Resolved FTIR Spectroscopy. Top. Catal. 2017, 60, 1709– 1721, DOI: 10.1007/s11244-017-0849-2Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSltrzF&md5=b353671365998a04ac659c00c36700d7Mechanism of Low Pressure Plasma-Assisted CO2 Hydrogenation Over Ni-USY by Microsecond Time-resolved FTIR SpectroscopyAzzolina-Jury, Federico; Thibault-Starzyk, FredericTopics in Catalysis (2017), 60 (19-20), 1709-1721CODEN: TOCAFI; ISSN:1022-5528. (Springer)Zeolite H-USY doped with nickel (14% wt.) was used as a catalyst in the plasma-assisted CO2 hydrogenation under partial vacuum. CO was found to be the main product of the reaction and it is generated by plasma-assisted CO2 dissocn. in the gas phase. The CO2 mols. vibrationally excited by plasma are also adsorbed on metallic nickel as formates which are further transformed into linear carbonyls. These species are then hydrogenated to form methane. Since the catalyst presents a low basic behavior, methane is produced from hydrogenation of linear carbonyls on nickel surface rather than from carbonates species. A detailed mechanism for this reaction assisted by plasma (glow discharge) is proposed using Operando time-resolved FTIR spectroscopic data.
- 26Miao, B.; Ma, S. S. K.; Wang, X.; Su, H.; Chan, S. H. Catalysis Mechanisms of CO2 and CO Methanation. Catal. Sci. Technol. 2016, 6, 4048– 4058, DOI: 10.1039/C6CY00478DGoogle Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1WjtLw%253D&md5=1787ea860abd35a585b80a37fddfa7caCatalysis mechanisms of CO2 and CO methanationMiao, Bin; Ma, Su Su Khine; Wang, Xin; Su, Haibin; Chan, Siew HwaCatalysis Science & Technology (2016), 6 (12), 4048-4058CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)A review. Understanding the reaction mechanisms of CO2 and CO methanation processes is crit. towards the successful development of heterogeneous catalysts with better activity, selectivity, and stability. This review provides detailed mechanisms of methanation processes and undesired catalyst deactivation. We characterize the methanation processes into two categories: (1) associative scheme, in which hydrogen atoms are involved in the C-O bond breaking process, and (2) dissociative scheme, where C-O bond breaking takes place before hydrogenation. For the catalyst deactivation mechanisms, we highlight three important factors, i.e. sulfur poisoning, carbon deposition and metal sintering.
- 27Lalinde, J. A. H.; Roongruangsree, P.; Ilsemann, J.; Bäumer, M.; Kopyscinski, J. CO2 Methanation and Reverse Water Gas Shift Reaction. Kinetic Study Based on in situ Spatially-Resolved Measurements. Chem. Eng. J. 2020, 124629, DOI: 10.1016/j.cej.2020.124629Google ScholarThere is no corresponding record for this reference.
- 28Garbarino, G.; Bellotti, D.; Finocchio, E.; Magistri, L.; Busca, G. Methanation of Carbon Dioxide on Ru/Al2O3: Catalytic Activity and Infrared Study. Catal. Today 2016, 277, 21– 28, DOI: 10.1016/j.cattod.2015.12.010Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktlartA%253D%253D&md5=cea0207ef8f7ef5a5e8759be0d84da79Methanation of carbon dioxide on Ru/Al2O3: Catalytic activity and infrared studyGarbarino, Gabriella; Bellotti, Daria; Finocchio, Elisabetta; Magistri, Loredana; Busca, GuidoCatalysis Today (2016), 277 (Part_1), 21-28CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)3% Ru/Al2O3 catalyst is active in converting CO2 into methane at atm. pressure. At 673 K and above the thermodn. equil. is nearly attained. At 623 K CH4 yield is above 85%. CO selectivity increases by decreasing reactants partial pressure apparently more than expected by thermodn. The reaction order for CO2 partial pressure is confirmed to be zero, while that related to hydrogen pressure is near 0.38 and activation energy ranges 60-75 kJ/mol. Arrhenius plot demonstrates that only at reduced reactant partial pressure (3% CO2) or high contact times, a contribution due to some diffusional limitation is present. IR study shows that the H2-reduced catalyst has high-oxidn. state Ru oxide species able to oxidize CO to CO2 at 173-243 K, while after oxidn./redn. cycle the alumina surface acido-basic sites are freed and the catalyst surface contains both extended Ru metal particles and dispersed low valence Ru species. IR studies show that the formation of methane, both from CO and CO2, occurs when both surface carbonyl species and surface formate species are obsd. Starting from CO2, methane is formed already in the low temp. range, i.e., 523-573 K, even when CO is not obsd. in the gas phase.
- 29Fisher, I. A.; Bell, A. T. A Comparative Study of CO and CO2 Hydrogenation over Rh/SiO2. J. Catal. 1996, 162, 54– 65, DOI: 10.1006/jcat.1996.0259Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XlsVGns78%253D&md5=424ed47b81cca8aacd98625399d132cbA comparative study of CO and CO2 hydrogenation over Rh/SiO2Fisher, Ian A.; Bell, Alexis T.Journal of Catalysis (1996), 162 (1), 54-65CODEN: JCTLA5; ISSN:0021-9517. (Academic)The hydrogenation of CO and CO2 over Rh/SiO2 have been investigated for the purpose of identifying the similarities and differences between these two reaction systems. In-situ IR spectroscopy was used to characterize the surface of the catalyst. Exposure of the catalyst to CO or CO2 produced very similar IR spectra in which the principal features are those for linearly and bridge-bonded CO. In the case of CO2 adsorption, a band for weakly adsorbed CO2 could also be obsd. For identical reaction conditions the rate of CO2 hydrogenation to methane is higher than that for CO hydrogenation. The activation energy for CO hydrogenation is 23.2 kcal/mol and that for CO2 hydrogenation is 16.6 kcal/mol. The partial pressure dependences on H2 and COz (z = 1, 2) are 0.67 and -0.80, resp., for CO hydrogenation, and 0.53 and -0.46, resp., for CO2 hydrogenation. IR spectroscopy reveals that under reaction conditions the catalyst surface is nearly satd. by adsorbed CO. The spectra obsd. during CO and CO2 hydrogenation are similar, the principal difference being that the CO coverage during CO hydrogenation is somewhat higher than that during CO2 hydrogenation. The CO coverage is insensitive to H2 partial pressure, but increases slightly with increasing COz partial pressure. Transient-response expts. demonstrate that the adsorbed CO is a crit. intermediate in both reaction systems. It is proposed that the rate-detg. step in the formation of methane is the dissocn. of HCHO, produced by the stepwise hydrogenation of adsorbed CO. A rate expression derived from the proposed mechanism properly describes the exptl. obsd. reaction kinetics both under steady-state and transient-response conditions.
- 30Eckle, S.; Anfang, H.-G.; Behm, R. J. r. Reaction Intermediates and Side Products in the Methanation of CO and CO2 over Supported Ru Catalysts in H2-Rich Reformate Gases. J. Phys. Chem. C 2011, 115, 1361– 1367, DOI: 10.1021/jp108106tGoogle Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFaku7%252FO&md5=596ce5f0cf83867737ac26b8a0a43d19Reaction Intermediates and Side Products in the Methanation of CO and CO2 over Supported Ru Catalysts in H2-Rich Reformate GasesEckle, Stephan; Anfang, Hans-Georg; Behm, R. JuegenJournal of Physical Chemistry C (2011), 115 (4), 1361-1367CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Aiming at a mechanistic understanding of the CO and CO2 methanation reaction over supported Ru catalysts and the underlying phys. reasons, we have investigated the methanation of CO and CO2 over a Ru/zeolite and a Ru/Al2O3 catalyst, in idealized and CO2-rich reformate gases by in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) measurements, employing quant. steady-state isotope transient kinetic anal. (SSITKA) techniques. On the basis of the correlation between COad band intensity/COad coverage, CH4,ad/HCOad/formate band intensity, and the CH4 formation rate under steady-state conditions, HCOad is unambiguously identified as reaction intermediate species in the dominant reaction pathway for CO methanation on the Ru/Al2O3 catalyst. On the Ru/zeolite such species could not be detected. CO2 methanation proceeds via dissocn. to COad, which is subsequently methanated. Formation and decompn. of surface formates plays only a minor role in the latter reaction, they rather act as spectator species.
- 31Navarro-Jaén, S.; Navarro, J. C.; Bobadilla, L. F.; Centeno, M. A.; Laguna, O. H.; Odriozola, J. A. Size-Tailored Ru Nanoparticles Deposited over γ-Al2O3 for the CO2 Methanation Reaction. Appl. Surf. Sci. 2019, 483, 750– 761, DOI: 10.1016/j.apsusc.2019.03.248Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntVGmtr0%253D&md5=c125e51aca5b9a2204a927afcba35c02Size-tailored Ru nanoparticles deposited over γ-Al2O3 for the CO2 methanation reactionNavarro-Jaen, Sara; Navarro, Juan C.; Bobadilla, Luis F.; Centeno, Miguel A.; Laguna, Oscar H.; Odriozola, Jose A.Applied Surface Science (2019), 483 (), 750-761CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)By means of the polyol method, a series of 5 wt% Ru/Al2O3 catalysts was synthesized controlling the particle size of the ruthenium species. The physico-chem. characterization demonstrated the successful particle size control of the Ru species, in such a way that higher the Ru/PVP ratio, higher the Ru particle size. Moreover, there are evidences that suggest preferential growth of the RuO2 clusters depending on the Ru/PVP ratio. Regarding the catalytic activity during the CO2 methanation, the total conversion and the CH4 yield increased with the particle size of Ru. Nevertheless, a considerable enhancement of the catalytic performance of the most active system was evidenced at 4 bar, demonstrating the improvement of the thermodn. (superior total conversion) and kinetics (superior reaction rate) of the CO2 methanation at pressures above the atm. one. Finally, the in situ DRIFTS study allowed to establish that CO2 was dissocd. to CO* and O* species on the metallic Ru particles, followed by the consecutive hydrogenation of CO* towards CHO*, CH2O*, CH3O*, and finally CH4 mols., which were further desorbed from the catalyst. Thus from the mechanistic point of view, a suitable particle size of the Ru nanoparticles along with the high-pressure effects results in the enhancement of the availability of hydrogen and consequently in the formation of CHxO species that enhance the cleavage of the C-O bond, which is the rate-detg. step of the overall CO2 methanation process.
- 32Fajín, J. L. C.; Gomes, J. R. B.; Cordeiro, M. N. D. S. Mechanistic Study of Carbon Monoxide Methanation over Pure and Rhodium- or Ruthenium-Doped Nickel Catalysts. J. Phys. Chem. C 2015, 119, 16537– 16551, DOI: 10.1021/acs.jpcc.5b01837Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVOnsbjE&md5=1594987944927c316260c3efc6edeceeMechanistic Study of Carbon Monoxide Methanation over Pure and Rhodium- or Ruthenium-Doped Nickel CatalystsFajin, Jose L. C.; Gomes, Jose R. B.; D. S. Cordeiro, M. NataliaJournal of Physical Chemistry C (2015), 119 (29), 16537-16551CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Carbon monoxide (CO) methanation has been studied through periodic d. functional theory calcns. on flat and corrugated nickel surfaces. The effect of doping the catalyst was taken into account by impregnating the nickel surfaces with Rh or Ru atoms. It was found that the methanation of CO as well as the synthesis of methanol from CO and hydrogen (H2) evolve through the formyl (HCO) intermediate on all the surfaces considered. The formation of this intermediate is the most energy-consuming step on all surface models with the exception of the Rh- and Ru-doped Ni(110) surfaces. In the methanation reaction, the CO dissocn. is assisted by hydrogen atoms and it is the rate-detg. step. Also, surfaces displaying low-coordinated atoms are more reactive than flat surfaces for the dissociative reaction steps. The reaction route proposed for the formation of methanol from CO and H2 presents activation energy barrier maxima similar to those of CO methanation on pure nickel and Rh- or Ru-doped flat nickel surfaces. However, the CO methanation reaction is more likely than the methanol formation on the doped stepped nickel surfaces, which is in agreement with exptl. results available in the literature. Thus, the different behavior found for these two reactions on the corrugated doped surfaces can then be used in the optimization of Ni-based catalysts favoring the formation of methane over methanol.
- 33Liu, C.-j.; Xu, G.-h.; Wang, T. Non-Thermal Plasma Approaches in CO2 Utilization. Fuel Process. Technol. 1999, 58, 119– 134, DOI: 10.1016/S0378-3820(98)00091-5Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXhslOis7o%253D&md5=e9f56954680ce2a78b37c0b4aeb65e37Non-thermal plasma approaches in CO2 utilizationLiu, Chang-jun; Xu, Gen-hui; Wang, TimingFuel Processing Technology (1999), 58 (2-3), 119-134CODEN: FPTEDY; ISSN:0378-3820. (Elsevier Science B.V.)A review with 72 refs. CO2 is the final product of combustion of all fossil fuels. CO2 itself has little value by far, but it contributes >50% to the man-made greenhouse effect among all the greenhouse gases. There is still no proven technol. for the chem. utilization of such a plentiful carbon resource. Recently, non-thermal plasmas have been found to be effective in the activation of CO2 for the formation of more valuable hydrocarbons. The non-thermal plasma approaches can even be performed at ambient condition. In this review, the present state of carbon dioxide utilization via non-thermal plasmas is addressed.
- 34Gupta, N. M.; Kamble, V. S.; Rao, K. A.; Iyer, R. M. On the Mechanism of CO and CO2 Methanation over Ru/Molecular-Sieve Catalyst. J. Catal. 1979, 60, 57– 67, DOI: 10.1016/0021-9517(79)90067-8Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXnvFSqtQ%253D%253D&md5=d33354523f22401da628f303d83d50dfOn the mechanism of carbon monoxide and carbon dioxide methanation over ruthenium/molecular sieve catalystGupta, N. M.; Kamble, V. S.; Rao, K. Annaji; Iyer, R. M.Journal of Catalysis (1979), 60 (1), 57-67CODEN: JCTLA5; ISSN:0021-9517.Disproportionation of CO [630-08-0] and redn. of CO2 [124-38-9] on Ru/mol.-sieve catalyst and the subsequent hydrogenation of the species formed was studied at 400-575K using a through-flow microcatalytic reactor. The CO disproportionates on the catalyst to give active C and CO2; the active C thus formed reacts with H to give CH4 [74-82-8]. Unlike CO, CO2 becomes chemisorbed on the catalyst and is subsequently reduced by H to give CH4 through the intermediate formation of active C. The time and temp. dependence of the reactivity of the C was studied in detail and a mechanism of catalytic methanation of CO and CO2 through the formation of active C intermediate was proposed.
- 35Utaka, T.; Okanishi, T.; Takeguchi, T.; Kikuchi, R.; Eguchi, K. Water Gas Shift Reaction of Reformed Fuel over Supported Ru Catalysts. Appl. Catal., A 2003, 245, 343– 351, DOI: 10.1016/S0926-860X(02)00657-9Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXktVOntL4%253D&md5=2e67d4803162395b5e89736771f42871Water gas shift reaction of reformed fuel over supported Ru catalystsUtaka, Toshimasa; Okanishi, Takeou; Takeguchi, Tatsuya; Kikuchi, Ryuji; Eguchi, KoichiApplied Catalysis, A: General (2003), 245 (2), 343-351CODEN: ACAGE4; ISSN:0926-860X. (Elsevier Science B.V.)Precious metal catalysts (Ir, Pd, Pt, Rh and Ru) supported on Al2O3 and Ru catalysts on CeO2, La2O3, MgO, Nb2O5, Ta2O5, TiO2, V2O5 and ZrO2 were investigated for water gas shift reaction of reformed gas. Ru/V2O3 catalyst reduced at 400 °C in H2 demonstrated the highest activity for the shift reaction without producing methane. The activities for the shift reaction over Ru catalysts supported on different oxides were not correlated with BET surface area or Ru dispersion, but the activity depended on the chem. character of oxide supports. The catalyst supported on a strongly basic or acid oxide is not effective for the shift reaction. In the same series of catalysts like Ru/V2O3, the activity systematically changed with BET surface area and Ru dispersion.
- 36Gupta, N. M.; Kamble, V. S.; Iyer, R. M.; Thampi, K. R.; Gratzel, M. FTIR Studies on the CO, CO2 and H2 Co-Adsorption over Ru-RuOx/TiO2 Catalyst. Catal. Lett. 1993, 21, 245– 255, DOI: 10.1007/BF00769476Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXhslCgs70%253D&md5=0b075921d9f5c85ca82ec8f73a912dc1FTIR studies on the carbon monoxide, carbon dioxide and hydrogen co-adsorption over ruthenium - ruthenium oxide (RuOx)/titania catalystGupta, N. M.; Kamble, V. S.; Iyer, R. M.Catalysis Letters (1993), 21 (3-4), 245-55CODEN: CALEER; ISSN:1011-372X.FTIR spectra of a Ru-RuOx/TiO2 catalyst obtained during coadsorption of CO, CO2, and H2 at 300-500 K were the sum total of the corresponding spectra obsd. during methanation of individual oxides. The 2 oxides compete for metal sites and, at each temp., they reacted simultaneously to form distinct transient Ru(CO)n type species even though the nature, the stability, and the reactivity of these species are different in the 2 cases. The monocarbonyl species formed during adsorption/reaction of CO alone or of CO + H2 were bonded more strongly than those formed during the CO2 + H2 reaction.
- 37Zhang, S.-T.; Yan, H.; Wei, M.; Evans, D. G.; Duan, X. Hydrogenation Mechanism of Carbon Dioxide and Carbon Monoxide on Ru(0001) Surface: A Density Functional Theory Study. RSC Adv. 2014, 4, 30241– 30249, DOI: 10.1039/C4RA01655FGoogle Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFOjtb7F&md5=71ed6101f1ee6c477c3535112b0c31c9Hydrogenation mechanism of carbon dioxide and carbon monoxide on Ru(0001) surface: a density functional theory studyZhang, Shi-Tong; Yan, Hong; Wei, Min; Evans, David G.; Duan, XueRSC Advances (2014), 4 (57), 30241-30249CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Catalytic hydrogenation of CO2 or CO to chems./fuels is of great significance in chem. engineering and the energy industry. In this work, d. functional theory (DFT) calcns. were carried out to investigate the hydrogenation of CO2 and CO on Ru(0001) surface to shed light on the understanding of the reaction mechanism, searching new catalysts and improving reaction efficiency. The adsorption of intermediate species (e.g., COOH, CHO and CH), reaction mechanisms, reaction selectivity and kinetics were systematically investigated. The results showed that on Ru(0001) surface, CO2 hydrogenation starts with the formation of an HCOO intermediate and produces adsorbed CHO and O species, followed by CHO dissocn. to CH and O; while CO hydrogenation occurs via either a COH or CHO intermediate. Both the hydrogenation processes produce active C and CH species, which subsequently undergoes hydrogenation to CH4 or a carbon chain growth reaction. The kinetics study indicates that product selectivity (methane or liq. hydrocarbons) is detd. by the competition between the two most favorable reactions: CH + H and CH + CH. Methane is the predominant product with a high H2 fraction at normal reaction pressure; while liq. hydrocarbons are mainly produced with a large CO2/CO fraction at a relatively high pressure.
- 38Mukkavilli, S.; Wittmann, C.; Tavlarides, L. L. Carbon Deactivation of Fischer-Tropsch Ruthenium Catalyst. Ind. Eng. Chem. Process Des. Dev. 1986, 25, 487– 494, DOI: 10.1021/i200033a023Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xht12gsrg%253D&md5=df4ab09bb428a700d5fbc38e73127676Carbon deactivation of Fischer-Tropsch ruthenium catalystMukkavilli, Suryanarayana; Wittmann, Charles; Tavlarides, Lawerence L.Industrial & Engineering Chemistry Process Design and Development (1986), 25 (2), 487-94CODEN: IEPDAW; ISSN:0196-4305.C deactivation of a 0.5% Ru/γ-Al2O3 surface-impregnated catalyst was examd. by using a Berty continuously stirred gas-solid reactor (CSGSR)-gas chromatograph setup at 473-573 K/2-6 atm, with wt. hourly space velocity 0.85 and 16.5 h-1, H2/CO feed ratio 3 and 2%, and synthesis time, 0.5-5 h. C deposited in a synthesis run was measured by integrating the CH4 evolution profile during catalyst redn. at 723 K in H2. Significant amts. of C were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C2-4 hydrocarbons showed a max. during the initial stages of deactivation. The kinetic data were correlated by assuming both H-assisted CO dissocn. and hydrogenation of surface C were rate-detg. The temp. and pressure dependences of the turnover nos. for methanation and carbon deposition were detd.
- 39Mikhail, M.; Wang, B.; Jalain, R.; Cavadias, S.; Tatoulian, M.; Ognier, S.; Gálvez, M. E.; Da Costa, P. Plasma-Catalytic Hybrid Process for CO2 Methanation: Optimization of Operation Parameters. React. Kinet., Mech. Catal. 2018, 126, 629– 643, DOI: 10.1007/s11144-018-1508-8Google ScholarThere is no corresponding record for this reference.
- 40Wang, L.; Zhao, Y.; Liu, C.; Gong, W.; Guo, H. Plasma Driven Ammonia Decomposition on a Fe-Catalyst: Eliminating Surface Nitrogen Poisoning. Chem. Commun. 2013, 49, 3787– 3789, DOI: 10.1039/c3cc41301bGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXlsFait70%253D&md5=9c48ac0e000570346ba0988dab301b69Plasma driven ammonia decomposition on a Fe-catalyst: eliminating surface nitrogen poisoningWang, Li; Zhao, Yue; Liu, Chunyang; Gong, Weimin; Guo, HongchenChemical Communications (Cambridge, United Kingdom) (2013), 49 (36), 3787-3789CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Strongly adsorbed N atoms inhibit the ammonia decompn. reaction rate. Plasma-driven catalysis can solve this problem and increase the ammonia conversion from 7.8% to 99.9%; 15NH3 isotope tracing and optical emission spectroscopy show that gas-phase active species (NH3*, NH√) in the plasma zone facilitate the desorption step by an Eley-Rideal (E-R) interaction.
- 41Zhu, B.; Li, X.-S.; Liu, J.-L.; Liu, J.-B.; Zhu, X.; Zhu, A.-M. In-Situ Regeneration of Au Nanocatalysts by Atmospheric-Pressure Air Plasma: Significant Contribution of Water Vapor. Appl. Catal., B 2015, 179, 69– 77, DOI: 10.1016/j.apcatb.2015.05.020Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotFCktLs%253D&md5=74866b233caf417485dfb7222e437bb1In-situ regeneration of Au nanocatalysts by atmospheric-pressure air plasma: Significant contribution of water vaporZhu, Bin; Li, Xiao-Song; Liu, Jing-Lin; Liu, Jin-Bao; Zhu, Xiaobing; Zhu, Ai-MinApplied Catalysis, B: Environmental (2015), 179 (), 69-77CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)In-situ regeneration of deactivated Au nanocatalysts during CO oxidn., was conducted effectively by pure oxygen plasma, but poisoned by dry air plasma in our previous work (Appl. Catal. B2012, 119-120, 49-55). With extension of previous study, a simple and effective technique of atm.-pressure cold plasma of humid air is explored for in-situ regeneration of Au nanocatalysts. In comparison with ineffective regeneration by dry plasma, humid plasma using synthetic air (20% O2 balance N2) as discharge gas surprisingly exhibited effective regeneration performance over Au catalyst due to significant contribution of water vapor. After plasma regeneration for 5 min, the regeneration degree of Au catalysts significantly increased up to 98% under humid plasma in presence of 2.77 vol.% water, while decreased down to neg. 29% under dry plasma. To disclose the mechanism of water vapor contribution to greatly improved regeneration degree, the characterizations of regenerated catalysts, and the analyses of elec. discharge characteristics and gaseous products during the plasma regeneration were conducted. The significant contribution of water vapor embodies in that it speeds up the decompn. of carbonate species and simultaneously inhibits the formation of poisoning species of nitrogen oxides. Furthermore, normal air instead of synthetic air in humid plasma regeneration was implemented on the evaluations of the deactivated Au catalysts after a long-term reaction and during ten deactivation-regeneration cycles, which ensured the feasibility and reliability of in-situ plasma regeneration of Au nanocatalysts as a simple, effective and promising technique.
- 42Zhao, P.; He, Y.; Cao, D.-B.; Wen, X.; Xiang, H.; Li, Y. W.; Wang, J.; Jiao, H. High Coverage Adsorption and Co-Adsorption of CO and H2 on Ru(0001) from DFT and Thermodynamics. Phys. Chem. Chem. Phys. 2015, 17, 19446– 19456, DOI: 10.1039/C5CP02486BGoogle Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVyntLrK&md5=aacb1703acae2f29fa16feb182b4aab3High coverage adsorption and co-adsorption of CO and H2 on Ru(0001) from DFT and thermodynamicsZhao, Peng; He, Yurong; Cao, Dong-Bo; Wen, Xiaodong; Xiang, Hongwei; Li, Yong-Wang; Wang, Jianguo; Jiao, HaijunPhysical Chemistry Chemical Physics (2015), 17 (29), 19446-19456CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The adsorption and co-adsorption of CO and H2 at different coverages on p(4 × 4) Ru(0001) have been computed using periodic d. functional theory (GGA-RPBE) and atomistic thermodn. Only mol. CO adsorption is possible and the satn. coverage is 0.75 ML (nCO = 12) with CO mols. co-adsorbed at different sites and has a hexagonal adsorption pattern as found by LEED. Only dissociative H2 adsorption is possible and the satn. coverage is 1 ML (nH = 16) with H atoms at fcc. sites. The computed CO and H2 desorption patterns and temps. agree reasonably with the expts. under ultrahigh vacuum conditions. For CO and H2 co-adsorption (nCO + mH2; n = 1-6 and m = 7, 6, 5, 5, 3, 1), CO pre-coverage affects H adsorption strongly, and each pre-adsorbed CO mol. blocks 2H adsorption sites and H2 does not adsorb on the surface with CO pre-coverage larger than 0.44 ML (nCO = 7); all these are in full agreement with the expts. under ultrahigh vacuum conditions. The results provide the basis for exploring the mechanisms of catalytic conversion of synthesis gas.
- 43Diemant, T.; Rauscher, H.; Bansmann, J.; Behm, R. J. Coadsorption of Hydrogen and CO on Well-Defined Pt35Ru65/Ru(0001) Surface Alloys-Site Specificity Vs. Adsorbate-Adsorbate Interactions. Phys. Chem. Chem. Phys. 2010, 12, 9801– 9810, DOI: 10.1039/c003368eGoogle Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVantrfF&md5=41b6431d18e82ac88161e4cea6d49934Coadsorption of hydrogen and CO on well-defined Pt35Ru65/Ru(0001) surface alloys. Site specificity vs. adsorbate-adsorbate interactionsDiemant, Thomas; Rauscher, Hubert; Bansmann, Joachim; Behm, R. JuergenPhysical Chemistry Chemical Physics (2010), 12 (33), 9801-9810CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The coadsorption of CO and hydrogen on a structurally well-defined Pt35Ru65/Ru(0001) monolayer surface alloy and, for comparison, on Ru(0001) were investigated by temp. programmed desorption (TPD) and IR reflection absorption spectroscopy (IRAS). The data reveal distinct modifications in the H adsorption behavior and also in the CO adsorption properties compared to adsorption of the individual components both on the monometallic and on the bimetallic surface. These modifications are discussed on an at. scale, in a picture that involves adsorbate-adsorbate interactions and site-specific variations in the (local) adsorption properties of the bimetallic surface, due to electronic ligand and strain effects and geometric ensemble effects.
- 44Wang, X.; Hong, Y.; Shi, H.; Szanyi, J. Kinetic Modeling and Transient DRIFTS–MS Studies of CO2 Methanation over Ru/Al2O3 Catalysts. J. Catal. 2016, 343, 185– 195, DOI: 10.1016/j.jcat.2016.02.001Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xjt1Wltr0%253D&md5=e8f7695dde61aaa9a5fd16a98080faacKinetic modeling and transient DRIFTS-MS studies of CO2 methanation over Ru/Al2O3 catalystsWang, Xiang; Hong, Yongchun; Shi, Hui; Szanyi, JanosJournal of Catalysis (2016), 343 (), 185-195CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)CO2 methanation was investigated on 5% and 0.5% Ru/Al2O3 catalysts (Ru dispersions: ∼18% and ∼40%, resp.) by steady-state kinetic measurements and transient DRIFTS-MS. Methanation rates were higher over 5% Ru/Al2O3 than over 0.5% Ru/Al2O3. The measured activation energies, however, were lower on 0.5% Ru/Al2O3 than on 5% Ru/Al2O3. Transient DRIFTS-MS results demonstrated that direct CO2 dissocn. was negligible over Ru. CO2 has to first react with surface hydroxyls on Al2O3 to form bicarbonates, which, in turn, react with adsorbed H on Ru to produce adsorbed formate species. Formates, most likely at the metal/oxide interface, can react rapidly with adsorbed H forming adsorbed CO, only a portion of which is reactive toward adsorbed H, ultimately leading to CH4 formation. The unreactive CO mols. are in geminal form adsorbed on low-coordinated sites. The measured kinetics are fully consistent with a Langmuir-Hinshelwood type mechanism in which the H-assisted dissocn. of the reactive CO* is the rate-detg. step (RDS). The similar empirical rate expressions (rCH4 = kP0.1CO2P0.3-0.5H2) and DRIFTS-MS results on the two catalysts under both transient and steady-state conditions suggest that the mechanism for CO2 methanation does not change with Ru particle size under the studied exptl. conditions. Kinetic modeling results further indicate that the intrinsic activation barrier for the RDS is slightly lower on 0.5% Ru/Al2O3 than on 5% Ru/Al2O3. Due to the presence of unreactive adsorbed CO on low-coordinated Ru sites under reaction conditions, the larger fraction of such surface sites on 0.5% Ru/Al2O3 than on 5% Ru/Al2O3 is regarded as the main reason for the lower rates for CO2 methanation on 0.5% Ru/Al2O3.
- 45Cant, N. W.; Bell, A. T. Studies of Carbon Monoxide Hydrogenation over Ruthenium Using Transient Response Techniques. J. Catal. 1982, 73, 257– 271, DOI: 10.1016/0021-9517(82)90099-9Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XhtlSntLY%253D&md5=0477ea3f8c65fcd985d6aab1111471a0Studies of carbon monoxide hydrogenation over ruthenium using transient response techniquesCant, Noel W.; Bell, Alexis T.Journal of Catalysis (1982), 73 (2), 257-71CODEN: JCTLA5; ISSN:0021-9517.Transient response isotopic tracing was used together with in situ IR spectroscopy to elucidate the dynamics of several elementary processes believed to occur during CO hydrogenation over Ru catalysts. Chemisorbed CO exchanged rapidly with gas phase CO and under reaction conditions the 2 species were in equil. A similar conclusion was reached regarding the relation between gas phase H2 and adsorbed H atoms. The dissocn. of molecularly adsorbed CO to form at. C and O required vacant surface sites and was reversible. While CO is the principal adsorbed species present on the catalyst surface under reaction conditions, the catalyst also maintains a significant inventory of nonoxygenated C but no chemisorbed O. The rate at which nonoxygenated C undergoes hydrogenation is faster than the rate at which adsorbed CO is hydrogenated. This observation supports the hypothesis that the nonoxygenated C is an intermediate in CO hydrogenation.
- 46Carballo, J. M. G.; Finocchio, E.; García-Rodriguez, S.; Ojeda, M.; Fierro, J. L. G.; Busca, G.; Rojas, S. Insights into the Deactivation and Reactivation of Ru/TiO2 During Fischer–Tropsch Synthesis. Catal. Today 2013, 214, 2– 11, DOI: 10.1016/j.cattod.2012.09.018Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1aqsbjJ&md5=48629d46077f3abfd0b0050cbcd49bc2Insights into the deactivation and reactivation of Ru/TiO2 during Fischer-Tropsch synthesisCarballo, Juan Maria Gonzalez; Finocchio, Elisabetta; Garcia-Rodriguez, Sergio; Ojeda, Manuel; Fierro, Jose Luis Garcia; Busca, Guido; Rojas, SergioCatalysis Today (2013), 214 (), 2-11CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)The catalytic performance of Ru/TiO2 for the prodn. of hydrocarbons via Fischer-Tropsch synthesis (FTS) was evaluated in this work. Ru/TiO2 exhibits high CO conversion rates (523 K, 2.5 MPa H2, 1.25 MPa CO) that decrease significantly with time-onstream. To recover the initial catalytic performance, different treatments using H2 or air were tested. The evolution of the catalyst structure during FTS and after the re-activation protocols were explored by a combination of ex situ and in situ techniques. Ru agglomeration, oxidn., and formation of Ru-volatile species are not responsible for the obsd. deactivation. However, Raman and IR (FTIR) spectroscopy have confirmed the presence of coke and alkyl chains on the spent catalysts. These species hinder the adsorption of the reactants on the active sites and are the primary reason for the obsd. decrease in the catalytic activity. These carbonaceous species can be removed by severe thermal treatments in air. However, this latter treatment drastically alters the morphol. of the Ru/TiO2, which leads to a substantial loss of catalytic activity.
- 47Saoud, W. A.; Assadi, A. A.; Guiza, M.; Bouzaza, A.; Aboussaoud, W.; Ouederni, A.; Soutrel, I.; Wolbert, D.; Rtimi, S. Study of Synergetic Effect, Catalytic Poisoning and Regeneration Using Dielectric Barrier Discharge and Photocatalysis in a Continuous Reactor: Abatement of Pollutants in Air Mixture System. Appl. Catal., B 2017, 213, 53– 61, DOI: 10.1016/j.apcatb.2017.05.012Google ScholarThere is no corresponding record for this reference.
- 48Aziz, M. A. A.; Jalil, A. A.; Triwahyono, S.; Saad, M. W. A. CO2 Methanation over Ni-Promoted Mesostructured Silica Nanoparticles: Influence of Ni Loading and Water Vapor on Activity and Response Surface Methodology Studies. Chem. Eng. J. 2015, 260, 757– 764, DOI: 10.1016/j.cej.2014.09.031Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFOqsb3I&md5=d344ec260a7602fdbe7c65a6753eec69CO2 methanation over Ni-promoted mesostructured silica nanoparticles: Influence of Ni loading and water vapor on activity and response surface methodology studiesAziz, M. A. A.; Jalil, A. A.; Triwahyono, S.; Saad, M. W. A.Chemical Engineering Journal (Amsterdam, Netherlands) (2015), 260 (), 757-764CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)The effects of Ni loading and H2O vapor on the properties of Ni/mesoporous SiO2 nanoparticles (MSN) and CO2 methanation were studied. X-ray diffraction, N2 adsorption-desorption, and pyrrole-adsorbed IR spectroscopy results indicated that the increasing Ni loading (1-10%) decreased the crystallinity, surface area, and basic sites of the catalysts. The activity of CO2 methanation followed the order of 10Ni/MSN ≈ 5Ni/MSN > 3Ni/MSN > 1Ni/MSN. The balance between Ni and the basic-site concn. is vital for the high activity of CO2 methanation. All Ni/MSN catalysts exhibited a high stability at 623 K for >100 h. The presence of H2O vapor in the feed stream induced a neg. effect on the activity of CO2 methanation. The H2O vapor decreased the carbonyl species concn. on the surface of Ni/MSN, as evidenced by CO + H2O-adsorbed IR spectroscopy. The response surface methodol. expts. were designed with face-centered central composite design (FCCCD) by applying 24 factorial points, 8 axial points, and 2 replicates, with one response variable (CO2 conversion). The Pareto chart indicated that the reaction temp. had the largest effect for all responses. The optimum CO2 conversion was predicted from the response surface anal. as 85% at an operating treatment time of 6 h, reaction temp. of 614 K, gas hourly space velocity (GHSV) of 69105 mL g-1cat h-1, and H2/CO2 ratio of 3.68.
- 49Falbo, L.; Martinelli, M.; Visconti, C. G.; Lietti, L.; Bassano, C.; Deiana, P. Kinetics of CO2 Methanation on a Ru-Based Catalyst at Process Conditions Relevant for Power-to-Gas Applications. Appl. Catal., B 2018, 225, 354– 363, DOI: 10.1016/j.apcatb.2017.11.066Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFKmtL7P&md5=c379ca032bd0d3fcb35f2f3eefbe9516Kinetics of CO2 methanation on a Ru-based catalyst at process conditions relevant for Power-to-Gas applicationsFalbo, Leonardo; Martinelli, Michela; Visconti, Carlo Giorgio; Lietti, Luca; Bassano, Claudia; Deiana, PaoloApplied Catalysis, B: Environmental (2018), 225 (), 354-363CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)A 0.5% Ru/γ-Al2O3 catalyst is appropriate to carry out the Sabatier reaction (CO2 methanation) under process conditions relevant for the Power-to-Gas application and the authors provide a kinetic model able to describe the CO2 conversion over a wide range of process conditions, previously unexplored. To achieve these goals, the effects of feed gas compn. (H2/CO2 ratio and presence of diluents), space velocity, temp. and pressure on catalyst activity and selectivity are studied. The catalyst is found stable when operating over a wide range of CO2 conversion values, with CH4 selectivity always over 99% and no deactivation, even when working with C-rich gas streams. The effect of H2O on the catalyst performance is also studied and an inhibiting kinetic effect is pointed out. Eventually, the capacity of kinetic models taken from the literature to account for CO2 conversion under the explored exptl. conditions is assessed. The kinetic model proposed by Lunde and Kester in 1973 (J. Catal. 30(1973) 423) is able to describe satisfactorily the catalyst behavior in a wide range of CO2 conversion spanning from differential conditions to thermodn. equil., provided that a new set of kinetic parameters is used. However a better fitting can be achieved by using a modified kinetic model, accounting for the inhibiting effect of H2O on CO2 conversion rate.
- 50Bacariza, M. C.; Biset-Peiró, M.; Graça, I.; Guilera, J.; Morante, J.; Lopes, J. M.; Andreu, T.; Henriques, C. DBD Plasma-Assisted CO2 Methanation Using Zeolite-Based Catalysts: Structure Composition-Reactivity Approach and Effect of Ce as Promoter. J. CO2 Util. 2018, 26, 202– 211, DOI: 10.1016/j.jcou.2018.05.013Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpslOmurc%253D&md5=d126cf04757760c27a2f384f34136f9fDBD plasma-assisted CO2 methanation using zeolite-based catalysts: Structure composition-reactivity approach and effect of Ce as promoterBacariza, M. C.; Biset-Peiro, M.; Graca, I.; Guilera, J.; Morante, J.; Lopes, J. M.; Andreu, T.; Henriques, C.Journal of CO2 Utilization (2018), 26 (), 202-211CODEN: JCUOAJ; ISSN:2212-9839. (Elsevier Ltd.)In the present work the effects of the structure compn. in terms of Si/Al ratio and Ce addn. in the performances of Ni-based zeolites for CO2 methanation under DBD plasma-assisted catalysis were evaluated. Results were compared with the obtained for a com. Ni/γ-Al2O3 catalyst and all samples were tested both under thermal and non-thermal DBD plasma conditions. It was found that a higher Si/Al ratio led to better performances not only under thermal but, esp., under plasma conditions, which was attributed to the lower affinity of this sample to water and, thus, to a decrease in the inhibitory role of this compd. in Sabatier reaction. Furthermore, the addn. of Ce as promoter favored the dielec. properties of the materials and gave addnl. sites for CO2 activation leading to much better results than the obtained for a com. Ni/γ-Al2O3 sample and for the Ni/zeolite, esp. under plasma conditions. Indeed, the best zeolite of this work (NiCe/Zeolite) reported a CH4 yield of 75% with a power supply of 25W while, under the same conditions, the com. sample and the un-promoted Ni/Zeolite presented just 23% and 15%, CH4 yield, resp. To our knowledge, this is the first time that a structure-reactivity relationship is attempted with zeolite catalysts under DBD plasma-assisted methanation conditions at atm. pressure. These facts also indicate that an important route is being opened, allowing answering to the essential question "what are the important characteristics a catalyst must have to show a better performance under plasma-assisted catalysis".
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Abstract
Figure 1
Figure 1. Performance of NTP-activated catalytic CO2 hydrogenation as a function of voltage/input energy over the Ru/SiO2 and Ru/γ-Al2O3 catalysts in reference to the control experiments; (a) CO2 conversion and (b) CH4 yield. Experimental conditions: feed gas composition of CO2/H2/Ar = 1:3:3 and WHSV of 30,000 mL (STP) gcat–1 h–1.
Figure 2
Figure 2. Dependence of the reaction rate on pH2 and pCO2 under (a, c) thermal conditions (at 330 °C) and (b, d) NTP conditions.
Figure 3
Figure 3. In situ DRIFTS spectra of surface species for CO2 hydrogenation over the Ru/SiO2 catalyst under (a) the NTP-off condition with the feed gas of 3% CO2 + 9% H2 + Ar, (b) NTP-on condition with the feed gas (at 5.5 kV and 27.0 kHz), and (c) NTP-off condition with the feed gas. (d) Relative intensities of surface species as a function of time-on-stream recorded by in situ DRIFTS from (b) and relative intensity change of methane recorded in MS (Figure S9) during CO2 hydrogenation by NTP activation (at 5.5 kV and 27.0 kHz).
Figure 4
Figure 4. CO2, CO, and carbon conversions as a function of ToS in CO poisoning experiments with different CO/CO2 inlet molar ratios under (a) thermal condition (at 330 °C) and (b) NTP condition (at 6.5 kV and 21.0 kHz).
Figure 5
Figure 5. Long-term deactivation test with the CO2/CO/H2 mixtures, regeneration treatment under Ar, and catalysis in CO2/H2 over the Ru/SiO2 catalyst under (a) the thermal condition (at 330 °C) and (b) NTP condition (at 6.5 kV and 21.0 kHz). Experimental conditions: feed gas composition of H2/C = 3, CO/CO2 = 0.5, and WHSV of 30,000 mL (STP) gcat–1 h–1.
Figure 6
Figure 6. In situ DRIFTS spectra of surface species collected at 250 °C in the thermally activated CO hydrogenation over the Ru/SiO2 catalyst. (a) Initial feed composition: 3% CO + 9% H2+ Ar; (b) change to inert Ar; (c) variations of COad intensity from in situ DRIFTS and CH4 intensity from MS after switching to Ar at 250 °C; (d) change back to the feed: 3% CO + 9% H2 + Ar; (e) change to H2/Ar; (f) variations of COad intensity from in situ DRIFTS and CH4 intensity from MS after switching the feed to H2/Ar at 250 °C.
Figure 7
Figure 7. (a) Corresponding MS signals collected simultaneously from the DRIFTS cell as a function of time during the NTP-assisted CO hydrogenation over the Ru/SiO2 catalyst. In situ DRIFTS spectra of surface species for CO hydrogenation over the Ru/SiO2 catalyst under (b) the NTP-off condition with the feed gas of 3% CO + 9% H2 + Ar, (c, d) NTP-on condition with the feed gas (at 5.5 kV and 27.0 kHz), and (e) NTP-off condition with the feed gas. (f) Relative intensities of surface species as a function of ToS recorded in the in situ DRIFTS from (c) and (d) during CO hydrogenation under NTP (at 5.5 kV and 27.0 kHz).
Figure 8
Figure 8. In situ DRIFTS spectra of surface species for hydrogenation of CO2/CO over the Ru/SiO2 catalyst under (a, b) the NTP-on condition with the feed gas of 1.5% CO2 + 1.5% CO + 9% H2 + Ar (at 5.5 kV and 27.0 kHz), (c) relative intensities of surface species as a function of ToS recorded in the in situ DRIFTS from (a) and (b), and (d) NTP-off condition with the feed gas.
References
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- 2Neyts, E. C.; Ostrikov, K. K.; Sunkara, M. K.; Bogaerts, A. Plasma Catalysis: Synergistic Effects at the Nanoscale. Chem. Rev. 2015, 115, 13408– 13446, DOI: 10.1021/acs.chemrev.5b003622https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVanur7J&md5=439066c4ea870bce64f2f2f78e133727Plasma Catalysis: Synergistic Effects at the NanoscaleNeyts, Erik C.; Ostrikov, Kostya; Sunkara, Mahendra K.; Bogaerts, AnnemieChemical Reviews (Washington, DC, United States) (2015), 115 (24), 13408-13446CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)Thermal-catalytic gas processing is integral to many current industrial processes. Ever-increasing demands on conversion and energy efficiencies are a strong driving force for the development of alternative approaches. Similarly, synthesis of several functional materials (such as nanowires and nanotubes) demands special processing conditions. Plasma catalysis provides such an alternative, where the catalytic process is complemented by the use of plasmas that activate the source gas. This combination is often obsd. to result in a synergy between plasma and catalyst. This Review introduces the current state-of-the-art in plasma catalysis, including numerous examples where plasma catalysis has demonstrated its benefits or shows future potential, including CO2 conversion, hydrocarbon reforming, synthesis of nanomaterials, ammonia prodn., and abatement of toxic waste gases. The underlying mechanisms governing these applications, as resulting from the interaction between the plasma and the catalyst, render the process highly complex, and little is known about the factors leading to the often-obsd. synergy. This Review critically examines the catalytic mechanisms relevant to each specific application.
- 3Bogaerts, A.; Tu, X.; Whitehead, J. C.; Centi, G.; Lefferts, L.; Guaitella, O.; Azzolina-Jury, F.; Kim, H.-H.; Murphy, A. B.; Schneider, W. F.; Nozaki, T.; Hicks, J. C.; Rousseau, A.; Thevenet, F.; Khacef, A.; Carreon, M. The 2020 Plasma Catalysis Roadmap. J. Phys. D: Appl. Phys. 2020, 53, 443001, DOI: 10.1088/1361-6463/ab90483https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvV2hurzL&md5=d6d567f273f525184ef3c93f312ec55bThe 2020 plasma catalysis roadmapBogaerts, Annemie; Tu, Xin; Whitehead, J. Christopher; Centi, Gabriele; Lefferts, Leon; Guaitella, Olivier; Azzolina-Jury, Federico; Kim, Hyun-Ha; Murphy, Anthony B.; Schneider, William F.; Nozaki, Tomohiro; Hicks, Jason C.; Rousseau, Antoine; Thevenet, Frederic; Khacef, Ahmed; Carreon, MariaJournal of Physics D: Applied Physics (2020), 53 (44), 443001CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)A review. Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chems. and fuels, CH4 activation into hydrogen, higher hydrocarbons or oxygenates, and NH3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile org. compd. remediation, particulate matter and NOx removal. In addn., plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over 'conventional' catalysis, as outlined in the Introduction. However, a better insight into the underlying phys. and chem. processes is crucial. This can be obtained by expts. applying diagnostics, studying both the chem. processes at the catalyst surface and the physicochem. mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technol. needed to meet these challenges.
- 4Vakili, R.; Gholami, R.; Stere, C. E.; Chansai, S.; Chen, H.; Holmes, S. M.; Jiao, Y.; Hardacre, C.; Fan, X. Plasma-Assisted Catalytic Dry Reforming of Methane (DRM) over Metal-Organic Frameworks (MOFs)-Based Catalysts. Appl. Catal., B 2020, 260, 118195, DOI: 10.1016/j.apcatb.2019.1181954https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvVWiur7E&md5=9dff32f0db929667e743f170edc03d18Plasma-assisted catalytic dry reforming of methane (DRM) over metal-organic frameworks (MOFs)-based catalystsVakili, Reza; Gholami, Rahman; Stere, Cristina E.; Chansai, Sarayute; Chen, Huanhao; Holmes, Stuart M.; Jiao, Yilai; Hardacre, Christopher; Fan, XiaoleiApplied Catalysis, B: Environmental (2020), 260 (), 118195CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Plasma-assisted dry reforming of methane (DRM) was performed in a dielec. barrier discharge (DBD) reactor. The effect of different packing materials including ZrO2, UiO-67 MOF and PtNP@UiO-67 on plasma discharge was investigated, showing that ZrO2 suppressed the plasma generation while UiO-67 improves it due to its porous nature which favors the formation of filamentary microdischarges and surface discharges. The improved plasma discharge increased the conversion of CH4 and CO2 by about 18% and 10%, resp., compared to the plasma-alone mode. In addn., the distribution of hydrocarbon products changed from dominant C2H6 in the plasma-alone mode to C2H2 and C2H4 in the UiO-67 promoted plasma-assisted DRM. The UiO-67 MOF was stable in plasma, showing no significant changes in its properties under different treatment times, discharge powers and gases. Pt nanoparticles (NPs) on UiO-67 improved plasma-assisted DRM, esp. the selectivity due to the presence of surface reactions. Due to the dehydrogenation of hydrocarbons over Pt NPs, the selectivity to hydrocarbons decreased by 30%, compared to the UiO-67 packing. In situ diffuse reflectance IR Fourier transformed spectroscopy (DRIFTS) was carried out to probe the surface reactions on PtNP@UiO-67 catalyst, showing the decompn. of surface formats to CO and C2H4 dehydrogenation over the metallic Pt. The PtNP@UiO-67 catalyst showed good reusability in the plasma-assisted DRM, and H2 prodn. was improved by high CH4/CO2 molar ratio and low feed flow rate.
- 5Stere, C. E.; Anderson, J. A.; Chansai, S.; Delgado, J. J.; Goguet, A.; Graham, W. G.; Hardacre, C.; Taylor, S. F. R.; Tu, X.; Wang, Z.; Yang, H. Non-Thermal Plasma Activation of Gold-Based Catalysts for Low-Temperature Water-Gas Shift Catalysis. Angew. Chem., Int. Ed. 2017, 56, 5579– 5583, DOI: 10.1002/anie.2016123705https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmtVels74%253D&md5=0866dd49e5db42a6ec8e9766dc96cbd7Non-Thermal Plasma Activation of Gold-Based Catalysts for Low-Temperature Water-Gas Shift CatalysisStere, Cristina E.; Anderson, James A.; Chansai, Sarayute; Delgado, Juan Jose; Goguet, Alexandre; Graham, Willam G.; Hardacre, C.; Taylor, S. F. Rebecca; Tu, Xin; Wang, Ziyun; Yang, HuiAngewandte Chemie, International Edition (2017), 56 (20), 5579-5583CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Non-thermal plasma activation has been used to enable low-temp. water-gas shift over a Au/CeZrO4 catalyst. The activity obtained was comparable with that attained by heating the catalyst to 180 °C providing an opportunity for the hydrogen prodn. to be obtained under conditions where the thermodn. limitations are minimal. Using in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS), structural changes assocd. with the gold nanoparticles in the catalyst have been obsd. which are not found under thermal activation indicating a weakening of the Au-CO bond and a change in the mechanism of deactivation.
- 6Xu, S.; Chansai, S.; Stere, C.; Inceesungvorn, B.; Goguet, A.; Wangkawong, K.; Taylor, S. F. R.; Al-Janabi, N.; Hardacre, C.; Martin, P. A.; Fan, X. Sustaining Metal–Organic Frameworks for Water-Gas Shift Catalysis by Non-Thermal Plasma. Nat. Catal. 2019, 2, 142– 148, DOI: 10.1038/s41929-018-0206-26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGisb7P&md5=c93a4af37296622e4d5a7c96eaa5af93Sustaining metal-organic frameworks for water-gas shift catalysis by non-thermal plasmaXu, Shaojun; Chansai, Sarayute; Stere, Cristina; Inceesungvorn, Burapat; Goguet, Alexandre; Wangkawong, Kanlayawat; Taylor, S. F. Rebecca; Al-Janabi, Nadeen; Hardacre, Christopher; Martin, Philip A.; Fan, XiaoleiNature Catalysis (2019), 2 (2), 142-148CODEN: NCAACP; ISSN:2520-1158. (Nature Research)The limited thermal and water stability of metal-org. frameworks (MOFs) often restricts their applications in conventional catalysis that involve thermal treatment and/or use of water. Non-thermal plasma (NTP) is a promising technique that can overcome barriers in conventional catalysis. Here we report an example of an NTP-activated water-gas shift reaction (WGSR) over a MOF (HKUST-1). Significantly, the exceptional stability of HKUST-1 was sustained under NTP activation and in the presence of water, which led to a high specific rate of 8.8 h-1. We found that NTP-induced water dissocn. has a twofold promotion effect in WGSR, as it facilitates WGSR by supplying OH and sustains the stability and hence activity of HKUST-1. In situ characterization of HKUST-1 revealed the crit. role of open Cu sites in the binding of substrate mols. This study paves the way to utilize MOFs for a wider range of catalysis.
- 7Chen, H.; Mu, Y.; Shao, Y.; Chansai, S.; Xu, S.; Stere, C. E.; Xiang, H.; Zhang, R.; Jiao, Y.; Hardacre, C.; Fan, X. Coupling Non-Thermal Plasma with Ni Catalysts Supported on Beta Zeolite for Catalytic CO2 Methanation. Catal. Sci. Technol. 2019, 9, 4135– 4145, DOI: 10.1039/C9CY00590K7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlahurzJ&md5=d7b1d829bbeda9fb39041ba4f53d0629Coupling non-thermal plasma with Ni catalysts supported on BETA zeolite for catalytic CO2 methanationChen, Huanhao; Mu, Yibing; Shao, Yan; Chansai, Sarayute; Xu, Shaojun; Stere, Cristina E.; Xiang, Huan; Zhang, Rongxin; Jiao, Yilai; Hardacre, Christopher; Fan, XiaoleiCatalysis Science & Technology (2019), 9 (15), 4135-4145CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)Catalytic carbon dioxide (CO2) methanation is a promising and effective process for CO2 use and the prodn. of CH4 as an alternative to using natural gas. Nonthermal plasma (NTP) activation was proven to be highly effective in overcoming the thermodn. limitation of reactions under mild conditions and intensifying the CO2 hydrogenation process greatly. Herein, the authors present an example of NTP-assisted catalytic CO2 methanation over Ni catalysts (15%) supported on BETA zeolite employing lanthana (La) as the promoter. A NTP-assisted system presents remarkable catalytic performance in catalytic CO2 methanation without an external heat source. Significantly, the use of Na-form BETA zeolite and the addn. of La (i.e. 15Ni-20La/Na-BETA catalyst) resulted in an improvement in CO2 conversions, surpassing the 15Ni/H-BETA catalyst, i.e. a 7-fold increase in the turnover frequency, TOF (1.45 s-1vs. 0.21 s-1), and selectivity towards CH4 (up to ∼97%). The developed catalyst also exhibited excellent stability under NTP conditions, i.e. a stable performance over a 15 h longevity test (with a TOF of 1.44 ± 0.01 s-1). Comparative in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) characterization of the developed catalysts revealed that the introduction of La2O3 to the Ni catalyst provides more surface hydroxyl groups, and hence enhances CO2 methanation. Addnl., by analyzing the surface species over 15Ni-20La/Na-BETA comparatively under thermal and NTP conditions (by in situ DRIFTS anal.), probably both the Langmuir-Hinshelwood and Eley-Rideal mechanisms coexist in the NTP system due to the presence of dissocd. H species in the gas phase. Conversely, for the thermal system, the reaction has to go through reactions between the surface-dissocd. H and carbonate-like adsorbed CO2 via the Langmuir-Hinshelwood mechanism. The current mechanistic understanding of the NTP-activated system paves the way for the exploration of the reaction mechanisms/pathways of NTP-assisted catalytic CO2 methanation.
- 8Kim, J.; Go, D. B.; Hicks, J. C. Synergistic Effects of Plasma-Catalyst Interactions for CH4 Activation. Phys. Chem. Chem. Phys. 2017, 19, 13010– 13021, DOI: 10.1039/C7CP01322A8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmvVSiur4%253D&md5=cbc20ae16d132403e3ec0f5ec30fc3e0Synergistic effects of plasma-catalyst interactions for CH4 activationKim, Jongsik; Go, David B.; Hicks, Jason C.Physical Chemistry Chemical Physics (2017), 19 (20), 13010-13021CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The elucidation of catalyst surface-plasma interactions is a challenging endeavor and therefore requires thorough and rigorous assessment of the reaction dynamics on the catalyst in the plasma environment. The first step in quantifying and defining catalyst-plasma interactions is a detailed kinetic study that can be used to verify appropriate reaction conditions for comparison and to discover any unexpected behavior of plasma-assisted reactions that might prevent direct comparison. In this paper, we provide a kinetic evaluation of CH4 activation in a dielec. barrier discharge plasma in order to quantify plasma-catalyst interactions via kinetic parameters. The dry reforming of CH4 with CO2 was studied as a model reaction using Ni supported on γ-Al2O3 at temps. of 790-890 K under atm. pressure, where the partial pressures of CH4 (or CO2) were varied over a range of ≤25.3 kPa. Reaction performance was monitored by varying gas hourly space velocity, plasma power, bulk gas temp., and reactant concn. After correcting for gas-phase plasma reactions, a linear relationship was obsd. in the log of the measured rate const. with respect to reciprocal power (1/power). Although thermal catalysis displays typical Arrhenius behavior for this reaction, plasma-assisted catalysis occurs from a complex mixt. of sources and shows non-Arrhenius behavior. However, an energy barrier was obtained from the relationship between the reaction rate const. and input power to exhibit ≤∼20 kJ mol-1 (compared to ∼70 kJ mol-1 for thermal catalysis). Of addnl. importance, the energy barriers measured during plasma-assisted catalysis were relatively consistent with respect to variations in total flow rates, types of diluent, or bulk reaction temp. These exptl. results suggest that plasma-generated vibrationally-excited CH4 favorably interacts with Ni sites at elevated temps., which helps reduce the energy barrier required to activate CH4 and enhance CH4 reforming rates.
- 9Xu, S.; Chansai, S.; Shao, Y.; Xu, S.; Wang, Y.-c.; Haigh, S.; Mu, Y.; Jiao, Y.; Stere, C. E.; Chen, H.; Fan, X.; Hardacre, C. Mechanistic Study of Non-Thermal Plasma Assisted CO2 Hydrogenation over Ru Supported on MgAl Layered Double Hydroxide. Appl. Catal., B 2020, 268, 118752, DOI: 10.1016/j.apcatb.2020.1187529https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjtlartrs%253D&md5=97f29ffdda1fc83436a5c90ba25bc86cMechanistic study of non-thermal plasma assisted CO2 hydrogenation over Ru supported on MgAl layered double hydroxideXu, Shanshan; Chansai, Sarayute; Shao, Yan; Xu, Shaojun; Wang, Yi-chi; Haigh, Sarah; Mu, Yibing; Jiao, Yilai; Stere, Cristina E.; Chen, Huanhao; Fan, Xiaolei; Hardacre, ChristopherApplied Catalysis, B: Environmental (2020), 268 (), 118752CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Carbon dioxide (CO2) hydrogenation to value-added mols. is an attractive way to reduce CO2 emission via upgrading. Herein, non-thermal plasma (NTP) activated CO2 hydrogenation over Ru/MgAl layered double hydroxide (LDH) catalysts was performed. The catalysis under the NTP conditions enabled significantly higher CO2 conversions (∼85%) and CH4 yield (∼84%) at relatively low temps. compared with the conventional thermally activated catalysis. Regarding the catalyst prepn., it was found that the redn. temp. can affect the chem. state of the metal and metal-support interaction significantly, and thus altering the activity of the catalysts in NTP-driven catalytic CO2 hydrogenation. A kinetic study revealed that the NTP-catalysis has a lower activation energy (at ∼21 kJ mol-1) than that of the thermal catalysis (ca. 82 kJ mol-1), due to the alternative pathways enabled by NTP, which was confirmed by the comparative in situ diffuse reflectance IR Fourier (DRIFTS) coupled with mass spectrometry (MS) characterization of the catalytic systems.
- 10Chen, H.; Goodarzi, F.; Mu, Y.; Chansai, S.; Mielby, J. J.; Mao, B.; Sooknoi, T.; Hardacre, C.; Kegnæs, S.; Fan, X. Effect of Metal Dispersion and Support Structure of Ni/Silicalite-1 Catalysts on Non-Thermal Plasma (NTP) Activated CO2 Hydrogenation. Appl. Catal., B 2020, 272, 119013, DOI: 10.1016/j.apcatb.2020.11901310https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXotVGjurw%253D&md5=c2e667bbbdfffda1539207671745f59fEffect of metal dispersion and support structure of Ni/silicalite-1 catalysts on non-thermal plasma (NTP) activated CO2 hydrogenationChen, Huanhao; Goodarzi, Farnoosh; Mu, Yibing; Chansai, Sarayute; Mielby, Jerrik Joergen; Mao, Boyang; Sooknoi, Tawan; Hardacre, Christopher; Kegnaes, Soeren; Fan, XiaoleiApplied Catalysis, B: Environmental (2020), 272 (), 119013CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Non-thermal plasma (NTP) activated heterogeneous catalysis is a promising alternative to thermal catalysis for enabling many challenging reactions (e.g. catalytic CO2 hydrogenation) under mild conditions. However, the mechanistic insight into the interaction between highly energetic electrons and vibrationally-excited reactive species with metal catalyst is still lacking. Here, catalytically active Ni nanoparticles supported on silicalite-1 zeolites with different configurations regarding the location of Ni active sites and support pore structures were comparably investigated using catalytic CO2 hydrogenation under the thermal and NTP conditions. Exptl. results revealed that the performance of the NTP-catalysis depends on the configuration of the catalysts significantly. Specifically, catalysts with Ni active sites sit on the outer surface of zeolite crystals (i.e. microporous Ni/S1 and Ni/M-S1@Shell with steam-assisted recrystd. micro-meso-porous structure) showed relatively good catalytic performance at a low applied voltage of 6.0 kV. Conversely, the encapsulated catalyst with hierarchical meso-micro-porous structure (i.e. Ni/D-S1) which has relatively small (i.e. av. Ni particle sizes of 2.8±0.7 nm) and dispersed Ni nanoparticles (i.e. Ni dispersion of ca. 2.5%) demonstrated comparatively the best catalytic performance (i.e. CO2 conversion of ca. 75%) at 7.5 kV. Addnl., under the NTP conditions studied, Ni on carbon-templated mesoporous silicalite-1 (Ni/M-S1) showed the worst selectivity to CH4, which was attributed to the poor accessibility of Ni active sites encapsulated in the enclosed mesopores. This study demonstrated the crucial role of catalyst design in NTP activated catalysis.
- 11Gupta, N. M.; Londhe, V. P.; Kamble, V. S. Gas-Uptake, Methanation, and Microcalorimetric Measurements on the Coadsorption of CO and H2 over Polycrystalline Ru and a Ru/TiO2 Catalyst. J. Catal. 1997, 169, 423– 437, DOI: 10.1006/jcat.1997.171811https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXkslWmsLc%253D&md5=100e787e9c603f85b28fa15cc2f737fcGas-uptake, methanation, and microcalorimetric measurements on the coadsorption of CO and H2 over polycrystalline Ru and a Ru/TiO2 catalystGupta, N. M.; Londhe, V. P.; Kamble, V. S.Journal of Catalysis (1997), 169 (2), 423-437CODEN: JCTLA5; ISSN:0021-9517. (Academic)The adsorption, methanation, and heat evolved over a Ru/TiO2 catalyst were found to be quite different than that over a polycryst. Ru sample, when exposed to CO+H2 (1:4) pulses at different temps. in the range 300-470 K. The coadsorbed H2 is found to have a large promotional effect on the CO uptake by the Ru/TiO2 catalyst, the extent of which depended on the catalyst temp. and the surface coverage. No such effect was obsd. in the case of Ru metal. Thus, while using Ru/TiO2 the ratio H2(ad)/CO(ad) increased progressively from 0.7 to 4 with the rise in catalyst temp. from 300 to 470 K, it was almost const. at ∼5±0.5 in the case of ruthenium metal. The exposure of Ru metal to CO+H2 (1:4) pulses gave rise to a differential heat of adsorption (qd)∼50 kJ mol-1 at all the reaction temps. under study, which corresponded to adsorption of CO and H2 mols. at distinct metal sites and in 1:1 stoichiometry. In the presence of excess H2, a qd value of ∼180-190 kJ mol-1 was obsd. at the reaction temps. above 425 K, suggesting the simultaneous hydrogenation of Cs species formed during CO dissocn. Contrary to this, a qd∼115 kJ mol-1 was obsd. for the CO+H2 (1:4) pulse injection over Ru/TiO2 at 300 K, the value reducing to ∼70 kJ mol-1 at higher reaction temps. Furthermore, a lower qd value (∼50 kJ mol-1) was obsd. during CO adsorption over Ru/TiO2 at 300 K in the presence of excess H2, which increased to ∼250 kJ mol-1 for the sample temps. of 420 and 470 K. These data are consistent with the FTIR spectroscopy results on CO+H2 adsorption over Ru/TiO2 catalyst, showing the formation of Ru(CO)n, RuH(CO)n, and RuH(CO)n-1 type surface complexes (n = 2 or 3) in addn. to the linear or the bridge-bonded CO mols. held at the large metal cluster sites (RuxCO). The relative intensity of IR bands responsible to these species depended on the catalyst temp., the RuxCO species growing progressively with the temp. rise. In the case of Ru metal, the formation of only linearly held surface species is envisaged. Arguments are presented to suggest that the CO mols. adsorbed in the multicarbonyl form require lesser energy to dissoc. and are therefore responsible to the obsd. low temp. (<450 K) methanation activity of Ru/TiO2. On the other hand, the activity at the higher reaction temps., both for the Ru metal and for the Ru/TiO2 catalyst, arises due to dissocn. of the linearly or bridge-bonded CO mols. The Ru-Cn and Ru-C species formed during dissocn. of multicarbonyls and linearly bonded CO, resp., are envisaged to have different rates of graphitization, the former species causing a rapid catalyst deactivation at the lower temps.
- 12Falbo, L.; Visconti, C. G.; Lietti, L.; Szanyi, J. The Effect of CO on CO2 Methanation over Ru/Al2O3 Catalysts: A Combined Steady-State Reactivity and Transient DRIFT Spectroscopy Study. Appl. Catal., B 2019, 256, 117791, DOI: 10.1016/j.apcatb.2019.11779112https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGiu7nL&md5=272f5842bc35813fcfab95ea86fe5753The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy studyFalbo, Leonardo; Visconti, Carlo G.; Lietti, Luca; Szanyi, JanosApplied Catalysis, B: Environmental (2019), 256 (), 117791CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)The reactivity of Ru/Al2O3 catalysts in the hydrogenation of CO/CO2 gas stream is investigated in this work to assess the possibility of carrying out CO2 methanation even in the presence of CO in the feed stream. Such a goal is pursued by conducting reactivity studies at process conditions of industrial interest (i.e., at high COx per-pass conversion and with concd. COx/H2 streams) and by monitoring the surface species on the catalyst through transient DRIFTS-MS anal. The catalyst shows gradual deactivation when the methanation is carried out in the presence of CO in the gas feed at low temps. (200-300 °C). However, stable performance is obsd. at higher temps., showing CH4 yields even higher than those obsd. during methanation of a pure CO2 feed. DRIFTS-MS expts. agree with a CO2 methanation pathway where CO2 is adsorbed as bicarbonate on Al2O3 and successively hydrogenated to methane on Ru, passing through formate and carbonyl intermediates. In the presence of CO at low temp., the catalyst shows a higher CO coverage of the Ru sites, a larger formate coverage of the alumina sites and the presence of adsorbed carbonaceous species, identified as carboxylate and hydrocarbon species. By carrying out the CO2 hydrogenation on the deactivated catalyst, carboxylates remain on the surface, effectively blocking CO2 adsorption sites. However, the catalyst deactivation at low temp. is reversible as thermal treatment (>350 °C) is able to restore the catalytic activity. Notably, working above the carboxylate decompn. temp. ensures a clean catalyst surface without high CO coverage, resulting in stable and high performance in CO/CO2 methanation.
- 13Barboun, P.; Mehta, P.; Herrera, F. A.; Go, D. B.; Schneider, W. F.; Hicks, J. C. Distinguishing Plasma Contributions to Catalyst Performance in Plasma-Assisted Ammonia Synthesis. ACS Sustainable Chem. Eng. 2019, 7, 8621– 8630, DOI: 10.1021/acssuschemeng.9b0040613https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntlGmu7g%253D&md5=b1b39b8c5db84217b0cf1ada9b614bd7Distinguishing Plasma Contributions to Catalyst Performance in Plasma-Assisted Ammonia SynthesisBarboun, Patrick; Mehta, Prateek; Herrera, Francisco A.; Go, David B.; Schneider, William F.; Hicks, Jason C.ACS Sustainable Chemistry & Engineering (2019), 7 (9), 8621-8630CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Plasma-assisted catalysis is the process of elec. activating gases in the plasma-phase at low temps. and ambient pressure to drive reactions on catalyst surfaces. Plasma-assisted catalytic processes combine conventional heterogeneous surface reactions, homogeneous plasma phase reactions, and coupling between plasma-generated species and the catalyst surface. Herein, we perform kinetically controlled ammonia synthesis measurements in a dielec. barrier discharge (DBD) plasma-assisted catalytic reactor. We decouple contributions due to plasma phase reactions from the overall plasma-assisted catalytic kinetics by performing plasma-only expts. By varying the gas compn., temp., and discharge power, we probe how macroscopic reaction conditions affect plasma-assisted ammonia synthesis on three different γ-alumina-supported transition metal catalysts (Ru, Co, and Ni). Our expts. indicate that the overall reaction and plasma-phase reaction are first-order in both N2 and H2. In contrast, the rate contributions due to plasma-catalyst interactions are first-order in N2 but zeroth order in H2. Furthermore, we find that the tuning of the plasma discharge power is more effective in controlling catalytic performance than the increasing of bulk gas temp. in plasma-assisted ammonia synthesis. Finally, we show that adding a catalyst to the DBD reaction alters the way that productivity scales with the specific energy input (SEI).
- 14Whitehead, J. C. Plasma–Catalysis: The Known Knowns, the Known Unknowns and the Unknown Unknowns. J. Phys. D: Appl. Phys. 2016, 49, 243001, DOI: 10.1088/0022-3727/49/24/24300114https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1Ort73F&md5=a2e794e822409e646c750b94854d7b87Plasma-catalysis: the known knowns, the known unknowns and the unknown unknownsWhitehead, J. ChristopherJournal of Physics D: Applied Physics (2016), 49 (24), 243001/1-243001/24CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)This review describes the history and development of plasma-assisted catalysis focussing mainly on the use of atm. pressure, non-thermal plasma. It identifies the various interactions between the plasma and the catalyst that can modify and activate the catalytic surface and also describes how the catalyst affects the properties of the discharge. Techniques for in situ diagnostics of species adsorbed onto the surface and present in the gas-phase over a range of timescales are described. The effect of temp. on plasma-catalysis can assist in detg. differences between thermal catalysis and plasma-activated catalysis and focuses on the meaning of temp. in a system involving non-equil. plasma. It can also help to develop an understanding of the gas phase and surface mechanism of the plasma-catalysis at a mol. level. Our current state of knowledge and ignorance is highlighted and future directions suggested.
- 15Gibson, E. K.; Stere, C. E.; Curran-McAteer, B.; Jones, W.; Cibin, G.; Gianolio, D.; Goguet, A.; Wells, P. P.; Catlow, C. R. A.; Collier, P.; Hinde, P.; Hardacre, C. Probing the Role of a Non-Thermal Plasma (NTP) in the Hybrid NTP Catalytic Oxidation of Methane. Angew. Chem., Int. Ed. 2017, 56, 9351– 9355, DOI: 10.1002/anie.20170355015https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFegu77J&md5=16ef0b1bf0d349e0b70eff5f0c20a045Probing the Role of a Non-Thermal Plasma (NTP) in the Hybrid NTP Catalytic Oxidation of MethaneGibson, Emma K.; Stere, Cristina E.; Curran-McAteer, Bronagh; Jones, Wilm; Cibin, Giannantonio; Gianolio, Diego; Goguet, Alexandre; Wells, Peter P.; Catlow, C. Richard A.; Collier, Paul; Hinde, Peter; Hardacre, ChristopherAngewandte Chemie, International Edition (2017), 56 (32), 9351-9355CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Three recurring hypotheses are often used to explain the effect of non-thermal plasmas (NTPs) on NTP catalytic hybrid reactions; namely, modification or heating of the catalyst or creation of new reaction pathways by plasma-produced species. NTP-assisted methane (CH4) oxidn. over Pd/Al2O3 was investigated by direct monitoring of the X-ray absorption fine structure of the catalyst, coupled with end-of-pipe mass spectrometry. This in situ study revealed that the catalyst did not undergo any significant structural changes under NTP conditions. However, the NTP did lead to an increase in the temp. of the Pd nanoparticles; although this temp. rise was insufficient to activate the thermal CH4 oxidn. reaction. The contribution of a lower activation barrier alternative reaction pathway involving the formation of CH3(g) from electron impact reactions is proposed.
- 16Mei, D.; Zhu, X.; He, Y.-L.; Yan, J. D.; Tu, X. Plasma-Assisted Conversion of CO2 in a Dielectric Barrier Discharge Reactor: Understanding the Effect of Packing Materials. Plasma Sources Sci. Technol. 2014, 24, 015011 DOI: 10.1088/0963-0252/24/1/015011There is no corresponding record for this reference.
- 17Mehta, P.; Barboun, P.; Go, D. B.; Hicks, J. C.; Schneider, W. F. Catalysis Enabled by Plasma Activation of Strong Chemical Bonds: A Review. ACS Energy Lett. 2019, 4, 1115– 1133, DOI: 10.1021/acsenergylett.9b0026317https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXmslGgur4%253D&md5=c3b7ed533387042051d12feeba67b4e0Catalysis Enabled by Plasma Activation of Strong Chemical Bonds: A ReviewMehta, Prateek; Barboun, Patrick; Go, David B.; Hicks, Jason C.; Schneider, William F.ACS Energy Letters (2019), 4 (5), 1115-1133CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Nonthermal plasma-driven catalysis is an emerging subfield of heterogeneous catalysis that is particularly promising for the chem. transformation of hard-to-activate mols. (e.g., N2, CO2, CH4). In this Review, we illustrate this promise of plasma-enhanced catalysis, focusing on the ammonia synthesis and methane dry reforming reactions, two reactions that have received wide attention and that illustrate the potential for plasma excitations to mitigate kinetic and thermodn. obstacles to chem. conversions. We highlight how plasma activation of reactants can provide access to overall reaction rates, conversions, product yields, and/or product distributions unattainable by thermal catalysis at similar temps. and pressures. Particular emphasis is given to efforts aimed at discerning the underlying mechanisms at play in these systems. We discuss opportunities for and challenges to the advancement of the field.
- 18Zhang, Y.; Wang, H.-y.; Jiang, W.; Bogaerts, A. Two-Dimensional Particle-in Cell/Monte Carlo Simulations of a Packed-Bed Dielectric Barrier Discharge in Air at Atmospheric Pressure. New J. Phys. 2015, 17, 083056 DOI: 10.1088/1367-2630/17/8/08305618https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XksFyqsrs%253D&md5=9aac45a820d39f05882942c076e63844Two-dimensional particle-in cell/Monte Carlo simulations of a packed-bed dielectric barrier discharge in air at atmospheric pressureZhang, Ya; Wang, Hong-yu; Jiang, Wei; Bogaerts, AnnemieNew Journal of Physics (2015), 17 (Aug.), 083056/1-083056/12CODEN: NJOPFM; ISSN:1367-2630. (IOP Publishing Ltd.)The plasma behavior in a parallel-plate dielec. barrier discharge (DBD) is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model, comparing for the first time an unpacked (empty)DBD with a packed bed DBD, i.e., a DBD filled with dielec. spheres in the gas gap. The calcns. are performed in air, at atm. pressure. The discharge is powered by a pulse with a voltage amplitude of-20 kV. When comparing the packed and unpacked DBD reactors with the same dielec. barriers, it is clear that the presence of the dielec. packing leads to a transition in discharge behavior from a combination of neg. streamers and unlimited surface streamers on the bottom dielec. surface to a combination of predominant pos. streamers and limited surface discharges on the dielec. surfaces of the beads and plates. Furthermore, in the packed bed DBD, the elec. field is locally enhanced inside the dielec. material, near the contact points between the beads and the plates, and therefore also in the plasma between the packing beads and between a bead and the dielec.-wall, leading to values of 4 × 108 Vm-1, which is much higher than the elec. field in the empty DBD reactor, i.e., in the order of 2 × 107 Vm-1, thus resulting in stronger and faster development of the plasma, and also in a higher electron d. The locally enhanced elec. field and the electron d. in the case of a packed bed DBD are also examd. and discussed for three different dielec. consts., i.e., ∈r = 22 (ZrO2), ∈r = 9 (Al2O3) and ∈r = 4 (SiO2). The enhanced elec. field is stronger and the electron d. is higher for a larger dielec. const., because the dielec. material is more effectively polarized. These simulations are very important, because of the increasing interest in packed bed DBDs for environmental applications.
- 19Zhang, K.; Zhang, G.; Liu, X.; Phan, A. N.; Luo, K. A Study on CO2 Decomposition to CO and O2 by the Combination of Catalysis and Dielectric-Barrier Discharges at Low Temperatures and Ambient Pressure. Ind. Eng. Chem. Res. 2017, 56, 3204– 3216, DOI: 10.1021/acs.iecr.6b0457019https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjtlCntrs%253D&md5=c1a4233364eec60381a97cd5cd8a9aabA Study on CO2 Decomposition to CO and O2 by the Combination of Catalysis and Dielectric-Barrier Discharges at Low Temperatures and Ambient PressureZhang, Kui; Zhang, Guangru; Liu, Xiaoteng; Phan, Anh N.; Luo, KunIndustrial & Engineering Chemistry Research (2017), 56 (12), 3204-3216CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)CO2 decompn. to CO and O2 was investigated in a dielec.-barrier discharge (DBD) reactor packed with BaTiO3 balls, glass beads with different sizes, and a mixt. of a Ni/SiO2 catalyst and BaTiO3 balls at lower temps. and ambient pressure. The property of packing beads and the reactor configuration affected the reaction significantly. The Ni/SiO2 catalyst samples were characterized by SEM, XRD, BET, and TEM. The combination of a DBD plasma and a Ni/SiO2 catalyst can enhance CO2 decompn. apparently, and a reaction mechanism of the plasma assisted CO2 dissocn. over the catalyst was proposed. In comparison with the result packed with glass balls (3 mm), the combination of BaTiO3 beads (3 mm) with a stainless steel mesh significantly enhanced the CO2 conversion and energy efficiency by a factor of 14.8, and that with a Ni/SiO2 catalyst by a factor of 11.5 in a DBD plasma at a specific input energy (SIE) of 55.2 kJ/L and low temps. (<115 °C).
- 20Zhang, Y.; Wang, H.-y.; Zhang, Y.-r.; Bogaerts, A. Formation of Microdischarges inside a Mesoporous Catalyst in Dielectric Barrier Discharge Plasmas. Plasma Sources Sci. Technol. 2017, 26, 054002 DOI: 10.1088/1361-6595/aa66be20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXjvVWqu7k%253D&md5=16c21f12c3fa10189001df4d7ced208fFormation of microdischarges inside a mesoporous catalyst in dielectric barrier discharge plasmasZhang, Ya; Wang, Hong-yu; Zhang, Yu-ru; Bogaerts, AnnemiePlasma Sources Science & Technology (2017), 26 (5), 054002/1-054002/18CODEN: PSTEEU; ISSN:1361-6595. (IOP Publishing Ltd.)The formation process of a microdischarge (MD) in both μm- and nm-sized catalyst pores is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model. A parallel-plate dielec. barrier discharge configuration in filamentary mode is considered in ambient air. The discharge is powered by a high voltage pulse. Our calcns. reveal that a streamer can penetrate into the surface features of a porous catalyst and MDs can be formed inside both μm- and nm-sized pores, yielding ionization inside the pore. For the μm-sized pores, the ionization mainly occurs inside the pore, while for the nm-sized pores the ionization is strongest near and inside the pore. Thus, enhanced discharges near and inside the mesoporous catalyst are obsd. Indeed, the max. values of the elec. field, ionization rate and electron d. occur near and inside the pore. The max. elec. field and electron d. inside the pore first increase when the pore size rises from 4 nm to 10 nm, and then they decrease for the 100 nm pore, due to a more pronounced surface discharge for the smaller pores. However, the ionization rate is highest for the 100 nm pore due to the largest effective ionization region.
- 21Weatherbee, G. D.; Bartholomew, C. H. Hydrogenation of CO2 on Group VIII Metals: II. Kinetics and Mechanism of CO2 Hydrogenation on Nickel. J. Catal. 1982, 77, 460– 472, DOI: 10.1016/0021-9517(82)90186-521https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXjsleqtQ%253D%253D&md5=9119a3bf4f58f7d6b915b03cbc663178Hydrogenation of carbon dioxide on Group VIII metals. II. Kinetics and mechanism of carbon dioxide hydrogenation on nickelWeatherbee, Gordon D.; Bartholomew, Calvin H.Journal of Catalysis (1982), 77 (2), 460-72CODEN: JCTLA5; ISSN:0021-9517.The rate of CO2 hydrogenation on Ni/SiO2 (140 kPa, 500-600 K, 30,000-90,000 h-1) is moderately dependent on CO2 and H concns. at low partial pressures but essentially concn. independent at high partial pressures. Under most typical reaction conditions CO is a reaction product at levels detd. by quasiequil. between surface and gas phase CO. Addn. of CO above this equil. level causes a significant decrease in the rate of CO2 hydrogenation, apparently as a result of product inhibition. Reaction orders and true activation energy are temp. dependent, indicating that a simple power law rate expression is inadequate. Kinetic results are consistent with a complex Langmuir-Hinshelwood mechanism involving dissociative adsorption of CO2 to CO and at. O followed by hydrogenation of CO via a C intermediate of CH4.
- 22Prairie, M. R.; Renken, A.; Highfield, J. G.; Thampi, K. R.; Grätzel, M. A Fourier Transform Infrared Spectroscopic Study of CO2 Methanation on Supported Ruthenium. J. Catal. 1991, 129, 130– 144, DOI: 10.1016/0021-9517(91)90017-X22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXitVKhu70%253D&md5=3e47d0a327b4aefc080b02561ec3723fFourier transform infrared spectroscopic study of carbon dioxide methanation on supported rutheniumPrairie, Michael R.; Renken, Albert; Highfield, James G.; Thampi, K. Ravindranathan; Graetzel, MichaelJournal of Catalysis (1991), 129 (1), 130-44CODEN: JCTLA5; ISSN:0021-9517.Diffuse-reflectance IR Fourier transform (DRIFT) spectroscopy was used to study in situ, the low-temp. (T <200°) methanation of CO2 over Ru on TiO2 and on Al2O3 supports. For 3.8% Ru/TiO2, the reaction exhibits an activation energy (Ea) of 19 kcal/mol, is 0.43 ± 0.05 order in H2 concn., and essentially independent of CO2 concn. At 110°, 40% of the available metal sites are occupied by CO (θCO = 0.4), a known methanation intermediate. In contrast to Ru/TiO2, Ru/Al2O3, despite having the same Ea and θCO = 0.2, is 15 times less active. Batch catalyst screening expts. showed no dependence of methanation activity on adsorbed CO(COa) formation rate (as modeled by HCOOH dehydration) or on θCO. In view of this, and the fact that CO dissocn. is structure-sensitive, heterogeneity in the active sites is invoked to reconcile the data. The high Ru dispersion on TiO2 is believed to contribute to the enhanced activity over this support. Adsorbed CO2 and H2 react, possibly at the metal-support interface, to form COa via rapid equilibration of the reverse water-gas shift reaction, in which HCOOH (and/or HCOO- ion) play a major role. According to this view, the COa and HCOOa- intermediates seen by FTIR represent accumulated reservoirs en route to CH4, in which the COa hydrogenation step is rate-controlling. An interesting synergy occurs for mixts. of Ru/anatase and Ru/rutile, the former being a better catalyst for COa supply while the latter is more effective in COa hydrogenation.
- 23Solymosi, F.; Erdöhelyi, A.; Kocsis, M. Methanation of CO2 on Supported Ru Catalysts. J. Chem. Soc., Faraday Trans. 1 1981, 77, 1003– 1012, DOI: 10.1039/f1981770100323https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXktlWjs7k%253D&md5=6066d7f89255617f89e12e4b43696046Methanation of carbon dioxide on supported ruthenium catalystsSolymosi, Frigyes; Erdohelyi, Andras; Kocsis, MariaJournal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases (1981), 77 (5), 1003-12CODEN: JCFTAR; ISSN:0300-9599.The transformation of C in the form of CO2 into hydrocarbons was studied on supported Ru catalysts. IR spectra showed that chemisorbed CO and [HCO2]- form during the coadsorption of H2 + CO2 at 373 K and during the methanation of CO2 at higher temps. The shift of the CO absorption band to lower frequencies was attributed to the effect of H adsorbed on the same Ru atoms and to surface C formed during the reaction. The [HCO2]- ions form on Ru atoms but migrate rapidly onto the support, thus being inactive in the methanation of CO2. The hydrogenation of CO2 on Ru/Al2O3 occurred at a measurable rate above 443 K yielding almost exclusively CH4. Surface C was detected during the reaction at a level ∼1.5 orders of magnitude less than in the H2 + CO reaction, indicating that the synthesis of CH4 occurs via the formation of surface C and its subsequent hydrogenation.
- 24Kuśmierz, M. Kinetic Study on Carbon Dioxide Hydrogenation over Ru/γ-Al2O3 Catalysts. Catal. Today 2008, 137, 429– 432, DOI: 10.1016/j.cattod.2008.03.00324https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXptlygu70%253D&md5=97e2263b31e1e86e39d3fb624ed322e4Kinetic study on carbon dioxide hydrogenation over Ru/γ-Al2O3 catalystsKusmierz, MarcinCatalysis Today (2008), 137 (2-4), 429-432CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Set of Ru/γ-Al2O3 catalysts prepd. by the DIM method was examd. in reaction of carbon dioxide hydrogenation. Overall apparent activation energy reaches a min. at ruthenium dispersion equal 0.5. Reaction order with respect to hydrogen decreases with H/Ru, while reaction order with respect to CO2 changes slightly within examd. dispersion range. Two interpretations of obsd. isokinetic effect, calcd. Tiso and corresponding wavenumber are presented.
- 25Azzolina-Jury, F.; Thibault-Starzyk, F. Mechanism of Low Pressure Plasma-Assisted CO2 Hydrogenation over Ni-USY by Microsecond Time-Resolved FTIR Spectroscopy. Top. Catal. 2017, 60, 1709– 1721, DOI: 10.1007/s11244-017-0849-225https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSltrzF&md5=b353671365998a04ac659c00c36700d7Mechanism of Low Pressure Plasma-Assisted CO2 Hydrogenation Over Ni-USY by Microsecond Time-resolved FTIR SpectroscopyAzzolina-Jury, Federico; Thibault-Starzyk, FredericTopics in Catalysis (2017), 60 (19-20), 1709-1721CODEN: TOCAFI; ISSN:1022-5528. (Springer)Zeolite H-USY doped with nickel (14% wt.) was used as a catalyst in the plasma-assisted CO2 hydrogenation under partial vacuum. CO was found to be the main product of the reaction and it is generated by plasma-assisted CO2 dissocn. in the gas phase. The CO2 mols. vibrationally excited by plasma are also adsorbed on metallic nickel as formates which are further transformed into linear carbonyls. These species are then hydrogenated to form methane. Since the catalyst presents a low basic behavior, methane is produced from hydrogenation of linear carbonyls on nickel surface rather than from carbonates species. A detailed mechanism for this reaction assisted by plasma (glow discharge) is proposed using Operando time-resolved FTIR spectroscopic data.
- 26Miao, B.; Ma, S. S. K.; Wang, X.; Su, H.; Chan, S. H. Catalysis Mechanisms of CO2 and CO Methanation. Catal. Sci. Technol. 2016, 6, 4048– 4058, DOI: 10.1039/C6CY00478D26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1WjtLw%253D&md5=1787ea860abd35a585b80a37fddfa7caCatalysis mechanisms of CO2 and CO methanationMiao, Bin; Ma, Su Su Khine; Wang, Xin; Su, Haibin; Chan, Siew HwaCatalysis Science & Technology (2016), 6 (12), 4048-4058CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)A review. Understanding the reaction mechanisms of CO2 and CO methanation processes is crit. towards the successful development of heterogeneous catalysts with better activity, selectivity, and stability. This review provides detailed mechanisms of methanation processes and undesired catalyst deactivation. We characterize the methanation processes into two categories: (1) associative scheme, in which hydrogen atoms are involved in the C-O bond breaking process, and (2) dissociative scheme, where C-O bond breaking takes place before hydrogenation. For the catalyst deactivation mechanisms, we highlight three important factors, i.e. sulfur poisoning, carbon deposition and metal sintering.
- 27Lalinde, J. A. H.; Roongruangsree, P.; Ilsemann, J.; Bäumer, M.; Kopyscinski, J. CO2 Methanation and Reverse Water Gas Shift Reaction. Kinetic Study Based on in situ Spatially-Resolved Measurements. Chem. Eng. J. 2020, 124629, DOI: 10.1016/j.cej.2020.124629There is no corresponding record for this reference.
- 28Garbarino, G.; Bellotti, D.; Finocchio, E.; Magistri, L.; Busca, G. Methanation of Carbon Dioxide on Ru/Al2O3: Catalytic Activity and Infrared Study. Catal. Today 2016, 277, 21– 28, DOI: 10.1016/j.cattod.2015.12.01028https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktlartA%253D%253D&md5=cea0207ef8f7ef5a5e8759be0d84da79Methanation of carbon dioxide on Ru/Al2O3: Catalytic activity and infrared studyGarbarino, Gabriella; Bellotti, Daria; Finocchio, Elisabetta; Magistri, Loredana; Busca, GuidoCatalysis Today (2016), 277 (Part_1), 21-28CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)3% Ru/Al2O3 catalyst is active in converting CO2 into methane at atm. pressure. At 673 K and above the thermodn. equil. is nearly attained. At 623 K CH4 yield is above 85%. CO selectivity increases by decreasing reactants partial pressure apparently more than expected by thermodn. The reaction order for CO2 partial pressure is confirmed to be zero, while that related to hydrogen pressure is near 0.38 and activation energy ranges 60-75 kJ/mol. Arrhenius plot demonstrates that only at reduced reactant partial pressure (3% CO2) or high contact times, a contribution due to some diffusional limitation is present. IR study shows that the H2-reduced catalyst has high-oxidn. state Ru oxide species able to oxidize CO to CO2 at 173-243 K, while after oxidn./redn. cycle the alumina surface acido-basic sites are freed and the catalyst surface contains both extended Ru metal particles and dispersed low valence Ru species. IR studies show that the formation of methane, both from CO and CO2, occurs when both surface carbonyl species and surface formate species are obsd. Starting from CO2, methane is formed already in the low temp. range, i.e., 523-573 K, even when CO is not obsd. in the gas phase.
- 29Fisher, I. A.; Bell, A. T. A Comparative Study of CO and CO2 Hydrogenation over Rh/SiO2. J. Catal. 1996, 162, 54– 65, DOI: 10.1006/jcat.1996.025929https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XlsVGns78%253D&md5=424ed47b81cca8aacd98625399d132cbA comparative study of CO and CO2 hydrogenation over Rh/SiO2Fisher, Ian A.; Bell, Alexis T.Journal of Catalysis (1996), 162 (1), 54-65CODEN: JCTLA5; ISSN:0021-9517. (Academic)The hydrogenation of CO and CO2 over Rh/SiO2 have been investigated for the purpose of identifying the similarities and differences between these two reaction systems. In-situ IR spectroscopy was used to characterize the surface of the catalyst. Exposure of the catalyst to CO or CO2 produced very similar IR spectra in which the principal features are those for linearly and bridge-bonded CO. In the case of CO2 adsorption, a band for weakly adsorbed CO2 could also be obsd. For identical reaction conditions the rate of CO2 hydrogenation to methane is higher than that for CO hydrogenation. The activation energy for CO hydrogenation is 23.2 kcal/mol and that for CO2 hydrogenation is 16.6 kcal/mol. The partial pressure dependences on H2 and COz (z = 1, 2) are 0.67 and -0.80, resp., for CO hydrogenation, and 0.53 and -0.46, resp., for CO2 hydrogenation. IR spectroscopy reveals that under reaction conditions the catalyst surface is nearly satd. by adsorbed CO. The spectra obsd. during CO and CO2 hydrogenation are similar, the principal difference being that the CO coverage during CO hydrogenation is somewhat higher than that during CO2 hydrogenation. The CO coverage is insensitive to H2 partial pressure, but increases slightly with increasing COz partial pressure. Transient-response expts. demonstrate that the adsorbed CO is a crit. intermediate in both reaction systems. It is proposed that the rate-detg. step in the formation of methane is the dissocn. of HCHO, produced by the stepwise hydrogenation of adsorbed CO. A rate expression derived from the proposed mechanism properly describes the exptl. obsd. reaction kinetics both under steady-state and transient-response conditions.
- 30Eckle, S.; Anfang, H.-G.; Behm, R. J. r. Reaction Intermediates and Side Products in the Methanation of CO and CO2 over Supported Ru Catalysts in H2-Rich Reformate Gases. J. Phys. Chem. C 2011, 115, 1361– 1367, DOI: 10.1021/jp108106t30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFaku7%252FO&md5=596ce5f0cf83867737ac26b8a0a43d19Reaction Intermediates and Side Products in the Methanation of CO and CO2 over Supported Ru Catalysts in H2-Rich Reformate GasesEckle, Stephan; Anfang, Hans-Georg; Behm, R. JuegenJournal of Physical Chemistry C (2011), 115 (4), 1361-1367CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Aiming at a mechanistic understanding of the CO and CO2 methanation reaction over supported Ru catalysts and the underlying phys. reasons, we have investigated the methanation of CO and CO2 over a Ru/zeolite and a Ru/Al2O3 catalyst, in idealized and CO2-rich reformate gases by in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) measurements, employing quant. steady-state isotope transient kinetic anal. (SSITKA) techniques. On the basis of the correlation between COad band intensity/COad coverage, CH4,ad/HCOad/formate band intensity, and the CH4 formation rate under steady-state conditions, HCOad is unambiguously identified as reaction intermediate species in the dominant reaction pathway for CO methanation on the Ru/Al2O3 catalyst. On the Ru/zeolite such species could not be detected. CO2 methanation proceeds via dissocn. to COad, which is subsequently methanated. Formation and decompn. of surface formates plays only a minor role in the latter reaction, they rather act as spectator species.
- 31Navarro-Jaén, S.; Navarro, J. C.; Bobadilla, L. F.; Centeno, M. A.; Laguna, O. H.; Odriozola, J. A. Size-Tailored Ru Nanoparticles Deposited over γ-Al2O3 for the CO2 Methanation Reaction. Appl. Surf. Sci. 2019, 483, 750– 761, DOI: 10.1016/j.apsusc.2019.03.24831https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntVGmtr0%253D&md5=c125e51aca5b9a2204a927afcba35c02Size-tailored Ru nanoparticles deposited over γ-Al2O3 for the CO2 methanation reactionNavarro-Jaen, Sara; Navarro, Juan C.; Bobadilla, Luis F.; Centeno, Miguel A.; Laguna, Oscar H.; Odriozola, Jose A.Applied Surface Science (2019), 483 (), 750-761CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)By means of the polyol method, a series of 5 wt% Ru/Al2O3 catalysts was synthesized controlling the particle size of the ruthenium species. The physico-chem. characterization demonstrated the successful particle size control of the Ru species, in such a way that higher the Ru/PVP ratio, higher the Ru particle size. Moreover, there are evidences that suggest preferential growth of the RuO2 clusters depending on the Ru/PVP ratio. Regarding the catalytic activity during the CO2 methanation, the total conversion and the CH4 yield increased with the particle size of Ru. Nevertheless, a considerable enhancement of the catalytic performance of the most active system was evidenced at 4 bar, demonstrating the improvement of the thermodn. (superior total conversion) and kinetics (superior reaction rate) of the CO2 methanation at pressures above the atm. one. Finally, the in situ DRIFTS study allowed to establish that CO2 was dissocd. to CO* and O* species on the metallic Ru particles, followed by the consecutive hydrogenation of CO* towards CHO*, CH2O*, CH3O*, and finally CH4 mols., which were further desorbed from the catalyst. Thus from the mechanistic point of view, a suitable particle size of the Ru nanoparticles along with the high-pressure effects results in the enhancement of the availability of hydrogen and consequently in the formation of CHxO species that enhance the cleavage of the C-O bond, which is the rate-detg. step of the overall CO2 methanation process.
- 32Fajín, J. L. C.; Gomes, J. R. B.; Cordeiro, M. N. D. S. Mechanistic Study of Carbon Monoxide Methanation over Pure and Rhodium- or Ruthenium-Doped Nickel Catalysts. J. Phys. Chem. C 2015, 119, 16537– 16551, DOI: 10.1021/acs.jpcc.5b0183732https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVOnsbjE&md5=1594987944927c316260c3efc6edeceeMechanistic Study of Carbon Monoxide Methanation over Pure and Rhodium- or Ruthenium-Doped Nickel CatalystsFajin, Jose L. C.; Gomes, Jose R. B.; D. S. Cordeiro, M. NataliaJournal of Physical Chemistry C (2015), 119 (29), 16537-16551CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Carbon monoxide (CO) methanation has been studied through periodic d. functional theory calcns. on flat and corrugated nickel surfaces. The effect of doping the catalyst was taken into account by impregnating the nickel surfaces with Rh or Ru atoms. It was found that the methanation of CO as well as the synthesis of methanol from CO and hydrogen (H2) evolve through the formyl (HCO) intermediate on all the surfaces considered. The formation of this intermediate is the most energy-consuming step on all surface models with the exception of the Rh- and Ru-doped Ni(110) surfaces. In the methanation reaction, the CO dissocn. is assisted by hydrogen atoms and it is the rate-detg. step. Also, surfaces displaying low-coordinated atoms are more reactive than flat surfaces for the dissociative reaction steps. The reaction route proposed for the formation of methanol from CO and H2 presents activation energy barrier maxima similar to those of CO methanation on pure nickel and Rh- or Ru-doped flat nickel surfaces. However, the CO methanation reaction is more likely than the methanol formation on the doped stepped nickel surfaces, which is in agreement with exptl. results available in the literature. Thus, the different behavior found for these two reactions on the corrugated doped surfaces can then be used in the optimization of Ni-based catalysts favoring the formation of methane over methanol.
- 33Liu, C.-j.; Xu, G.-h.; Wang, T. Non-Thermal Plasma Approaches in CO2 Utilization. Fuel Process. Technol. 1999, 58, 119– 134, DOI: 10.1016/S0378-3820(98)00091-533https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXhslOis7o%253D&md5=e9f56954680ce2a78b37c0b4aeb65e37Non-thermal plasma approaches in CO2 utilizationLiu, Chang-jun; Xu, Gen-hui; Wang, TimingFuel Processing Technology (1999), 58 (2-3), 119-134CODEN: FPTEDY; ISSN:0378-3820. (Elsevier Science B.V.)A review with 72 refs. CO2 is the final product of combustion of all fossil fuels. CO2 itself has little value by far, but it contributes >50% to the man-made greenhouse effect among all the greenhouse gases. There is still no proven technol. for the chem. utilization of such a plentiful carbon resource. Recently, non-thermal plasmas have been found to be effective in the activation of CO2 for the formation of more valuable hydrocarbons. The non-thermal plasma approaches can even be performed at ambient condition. In this review, the present state of carbon dioxide utilization via non-thermal plasmas is addressed.
- 34Gupta, N. M.; Kamble, V. S.; Rao, K. A.; Iyer, R. M. On the Mechanism of CO and CO2 Methanation over Ru/Molecular-Sieve Catalyst. J. Catal. 1979, 60, 57– 67, DOI: 10.1016/0021-9517(79)90067-834https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXnvFSqtQ%253D%253D&md5=d33354523f22401da628f303d83d50dfOn the mechanism of carbon monoxide and carbon dioxide methanation over ruthenium/molecular sieve catalystGupta, N. M.; Kamble, V. S.; Rao, K. Annaji; Iyer, R. M.Journal of Catalysis (1979), 60 (1), 57-67CODEN: JCTLA5; ISSN:0021-9517.Disproportionation of CO [630-08-0] and redn. of CO2 [124-38-9] on Ru/mol.-sieve catalyst and the subsequent hydrogenation of the species formed was studied at 400-575K using a through-flow microcatalytic reactor. The CO disproportionates on the catalyst to give active C and CO2; the active C thus formed reacts with H to give CH4 [74-82-8]. Unlike CO, CO2 becomes chemisorbed on the catalyst and is subsequently reduced by H to give CH4 through the intermediate formation of active C. The time and temp. dependence of the reactivity of the C was studied in detail and a mechanism of catalytic methanation of CO and CO2 through the formation of active C intermediate was proposed.
- 35Utaka, T.; Okanishi, T.; Takeguchi, T.; Kikuchi, R.; Eguchi, K. Water Gas Shift Reaction of Reformed Fuel over Supported Ru Catalysts. Appl. Catal., A 2003, 245, 343– 351, DOI: 10.1016/S0926-860X(02)00657-935https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXktVOntL4%253D&md5=2e67d4803162395b5e89736771f42871Water gas shift reaction of reformed fuel over supported Ru catalystsUtaka, Toshimasa; Okanishi, Takeou; Takeguchi, Tatsuya; Kikuchi, Ryuji; Eguchi, KoichiApplied Catalysis, A: General (2003), 245 (2), 343-351CODEN: ACAGE4; ISSN:0926-860X. (Elsevier Science B.V.)Precious metal catalysts (Ir, Pd, Pt, Rh and Ru) supported on Al2O3 and Ru catalysts on CeO2, La2O3, MgO, Nb2O5, Ta2O5, TiO2, V2O5 and ZrO2 were investigated for water gas shift reaction of reformed gas. Ru/V2O3 catalyst reduced at 400 °C in H2 demonstrated the highest activity for the shift reaction without producing methane. The activities for the shift reaction over Ru catalysts supported on different oxides were not correlated with BET surface area or Ru dispersion, but the activity depended on the chem. character of oxide supports. The catalyst supported on a strongly basic or acid oxide is not effective for the shift reaction. In the same series of catalysts like Ru/V2O3, the activity systematically changed with BET surface area and Ru dispersion.
- 36Gupta, N. M.; Kamble, V. S.; Iyer, R. M.; Thampi, K. R.; Gratzel, M. FTIR Studies on the CO, CO2 and H2 Co-Adsorption over Ru-RuOx/TiO2 Catalyst. Catal. Lett. 1993, 21, 245– 255, DOI: 10.1007/BF0076947636https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXhslCgs70%253D&md5=0b075921d9f5c85ca82ec8f73a912dc1FTIR studies on the carbon monoxide, carbon dioxide and hydrogen co-adsorption over ruthenium - ruthenium oxide (RuOx)/titania catalystGupta, N. M.; Kamble, V. S.; Iyer, R. M.Catalysis Letters (1993), 21 (3-4), 245-55CODEN: CALEER; ISSN:1011-372X.FTIR spectra of a Ru-RuOx/TiO2 catalyst obtained during coadsorption of CO, CO2, and H2 at 300-500 K were the sum total of the corresponding spectra obsd. during methanation of individual oxides. The 2 oxides compete for metal sites and, at each temp., they reacted simultaneously to form distinct transient Ru(CO)n type species even though the nature, the stability, and the reactivity of these species are different in the 2 cases. The monocarbonyl species formed during adsorption/reaction of CO alone or of CO + H2 were bonded more strongly than those formed during the CO2 + H2 reaction.
- 37Zhang, S.-T.; Yan, H.; Wei, M.; Evans, D. G.; Duan, X. Hydrogenation Mechanism of Carbon Dioxide and Carbon Monoxide on Ru(0001) Surface: A Density Functional Theory Study. RSC Adv. 2014, 4, 30241– 30249, DOI: 10.1039/C4RA01655F37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFOjtb7F&md5=71ed6101f1ee6c477c3535112b0c31c9Hydrogenation mechanism of carbon dioxide and carbon monoxide on Ru(0001) surface: a density functional theory studyZhang, Shi-Tong; Yan, Hong; Wei, Min; Evans, David G.; Duan, XueRSC Advances (2014), 4 (57), 30241-30249CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Catalytic hydrogenation of CO2 or CO to chems./fuels is of great significance in chem. engineering and the energy industry. In this work, d. functional theory (DFT) calcns. were carried out to investigate the hydrogenation of CO2 and CO on Ru(0001) surface to shed light on the understanding of the reaction mechanism, searching new catalysts and improving reaction efficiency. The adsorption of intermediate species (e.g., COOH, CHO and CH), reaction mechanisms, reaction selectivity and kinetics were systematically investigated. The results showed that on Ru(0001) surface, CO2 hydrogenation starts with the formation of an HCOO intermediate and produces adsorbed CHO and O species, followed by CHO dissocn. to CH and O; while CO hydrogenation occurs via either a COH or CHO intermediate. Both the hydrogenation processes produce active C and CH species, which subsequently undergoes hydrogenation to CH4 or a carbon chain growth reaction. The kinetics study indicates that product selectivity (methane or liq. hydrocarbons) is detd. by the competition between the two most favorable reactions: CH + H and CH + CH. Methane is the predominant product with a high H2 fraction at normal reaction pressure; while liq. hydrocarbons are mainly produced with a large CO2/CO fraction at a relatively high pressure.
- 38Mukkavilli, S.; Wittmann, C.; Tavlarides, L. L. Carbon Deactivation of Fischer-Tropsch Ruthenium Catalyst. Ind. Eng. Chem. Process Des. Dev. 1986, 25, 487– 494, DOI: 10.1021/i200033a02338https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xht12gsrg%253D&md5=df4ab09bb428a700d5fbc38e73127676Carbon deactivation of Fischer-Tropsch ruthenium catalystMukkavilli, Suryanarayana; Wittmann, Charles; Tavlarides, Lawerence L.Industrial & Engineering Chemistry Process Design and Development (1986), 25 (2), 487-94CODEN: IEPDAW; ISSN:0196-4305.C deactivation of a 0.5% Ru/γ-Al2O3 surface-impregnated catalyst was examd. by using a Berty continuously stirred gas-solid reactor (CSGSR)-gas chromatograph setup at 473-573 K/2-6 atm, with wt. hourly space velocity 0.85 and 16.5 h-1, H2/CO feed ratio 3 and 2%, and synthesis time, 0.5-5 h. C deposited in a synthesis run was measured by integrating the CH4 evolution profile during catalyst redn. at 723 K in H2. Significant amts. of C were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C2-4 hydrocarbons showed a max. during the initial stages of deactivation. The kinetic data were correlated by assuming both H-assisted CO dissocn. and hydrogenation of surface C were rate-detg. The temp. and pressure dependences of the turnover nos. for methanation and carbon deposition were detd.
- 39Mikhail, M.; Wang, B.; Jalain, R.; Cavadias, S.; Tatoulian, M.; Ognier, S.; Gálvez, M. E.; Da Costa, P. Plasma-Catalytic Hybrid Process for CO2 Methanation: Optimization of Operation Parameters. React. Kinet., Mech. Catal. 2018, 126, 629– 643, DOI: 10.1007/s11144-018-1508-8There is no corresponding record for this reference.
- 40Wang, L.; Zhao, Y.; Liu, C.; Gong, W.; Guo, H. Plasma Driven Ammonia Decomposition on a Fe-Catalyst: Eliminating Surface Nitrogen Poisoning. Chem. Commun. 2013, 49, 3787– 3789, DOI: 10.1039/c3cc41301b40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXlsFait70%253D&md5=9c48ac0e000570346ba0988dab301b69Plasma driven ammonia decomposition on a Fe-catalyst: eliminating surface nitrogen poisoningWang, Li; Zhao, Yue; Liu, Chunyang; Gong, Weimin; Guo, HongchenChemical Communications (Cambridge, United Kingdom) (2013), 49 (36), 3787-3789CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Strongly adsorbed N atoms inhibit the ammonia decompn. reaction rate. Plasma-driven catalysis can solve this problem and increase the ammonia conversion from 7.8% to 99.9%; 15NH3 isotope tracing and optical emission spectroscopy show that gas-phase active species (NH3*, NH√) in the plasma zone facilitate the desorption step by an Eley-Rideal (E-R) interaction.
- 41Zhu, B.; Li, X.-S.; Liu, J.-L.; Liu, J.-B.; Zhu, X.; Zhu, A.-M. In-Situ Regeneration of Au Nanocatalysts by Atmospheric-Pressure Air Plasma: Significant Contribution of Water Vapor. Appl. Catal., B 2015, 179, 69– 77, DOI: 10.1016/j.apcatb.2015.05.02041https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotFCktLs%253D&md5=74866b233caf417485dfb7222e437bb1In-situ regeneration of Au nanocatalysts by atmospheric-pressure air plasma: Significant contribution of water vaporZhu, Bin; Li, Xiao-Song; Liu, Jing-Lin; Liu, Jin-Bao; Zhu, Xiaobing; Zhu, Ai-MinApplied Catalysis, B: Environmental (2015), 179 (), 69-77CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)In-situ regeneration of deactivated Au nanocatalysts during CO oxidn., was conducted effectively by pure oxygen plasma, but poisoned by dry air plasma in our previous work (Appl. Catal. B2012, 119-120, 49-55). With extension of previous study, a simple and effective technique of atm.-pressure cold plasma of humid air is explored for in-situ regeneration of Au nanocatalysts. In comparison with ineffective regeneration by dry plasma, humid plasma using synthetic air (20% O2 balance N2) as discharge gas surprisingly exhibited effective regeneration performance over Au catalyst due to significant contribution of water vapor. After plasma regeneration for 5 min, the regeneration degree of Au catalysts significantly increased up to 98% under humid plasma in presence of 2.77 vol.% water, while decreased down to neg. 29% under dry plasma. To disclose the mechanism of water vapor contribution to greatly improved regeneration degree, the characterizations of regenerated catalysts, and the analyses of elec. discharge characteristics and gaseous products during the plasma regeneration were conducted. The significant contribution of water vapor embodies in that it speeds up the decompn. of carbonate species and simultaneously inhibits the formation of poisoning species of nitrogen oxides. Furthermore, normal air instead of synthetic air in humid plasma regeneration was implemented on the evaluations of the deactivated Au catalysts after a long-term reaction and during ten deactivation-regeneration cycles, which ensured the feasibility and reliability of in-situ plasma regeneration of Au nanocatalysts as a simple, effective and promising technique.
- 42Zhao, P.; He, Y.; Cao, D.-B.; Wen, X.; Xiang, H.; Li, Y. W.; Wang, J.; Jiao, H. High Coverage Adsorption and Co-Adsorption of CO and H2 on Ru(0001) from DFT and Thermodynamics. Phys. Chem. Chem. Phys. 2015, 17, 19446– 19456, DOI: 10.1039/C5CP02486B42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVyntLrK&md5=aacb1703acae2f29fa16feb182b4aab3High coverage adsorption and co-adsorption of CO and H2 on Ru(0001) from DFT and thermodynamicsZhao, Peng; He, Yurong; Cao, Dong-Bo; Wen, Xiaodong; Xiang, Hongwei; Li, Yong-Wang; Wang, Jianguo; Jiao, HaijunPhysical Chemistry Chemical Physics (2015), 17 (29), 19446-19456CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The adsorption and co-adsorption of CO and H2 at different coverages on p(4 × 4) Ru(0001) have been computed using periodic d. functional theory (GGA-RPBE) and atomistic thermodn. Only mol. CO adsorption is possible and the satn. coverage is 0.75 ML (nCO = 12) with CO mols. co-adsorbed at different sites and has a hexagonal adsorption pattern as found by LEED. Only dissociative H2 adsorption is possible and the satn. coverage is 1 ML (nH = 16) with H atoms at fcc. sites. The computed CO and H2 desorption patterns and temps. agree reasonably with the expts. under ultrahigh vacuum conditions. For CO and H2 co-adsorption (nCO + mH2; n = 1-6 and m = 7, 6, 5, 5, 3, 1), CO pre-coverage affects H adsorption strongly, and each pre-adsorbed CO mol. blocks 2H adsorption sites and H2 does not adsorb on the surface with CO pre-coverage larger than 0.44 ML (nCO = 7); all these are in full agreement with the expts. under ultrahigh vacuum conditions. The results provide the basis for exploring the mechanisms of catalytic conversion of synthesis gas.
- 43Diemant, T.; Rauscher, H.; Bansmann, J.; Behm, R. J. Coadsorption of Hydrogen and CO on Well-Defined Pt35Ru65/Ru(0001) Surface Alloys-Site Specificity Vs. Adsorbate-Adsorbate Interactions. Phys. Chem. Chem. Phys. 2010, 12, 9801– 9810, DOI: 10.1039/c003368e43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVantrfF&md5=41b6431d18e82ac88161e4cea6d49934Coadsorption of hydrogen and CO on well-defined Pt35Ru65/Ru(0001) surface alloys. Site specificity vs. adsorbate-adsorbate interactionsDiemant, Thomas; Rauscher, Hubert; Bansmann, Joachim; Behm, R. JuergenPhysical Chemistry Chemical Physics (2010), 12 (33), 9801-9810CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)The coadsorption of CO and hydrogen on a structurally well-defined Pt35Ru65/Ru(0001) monolayer surface alloy and, for comparison, on Ru(0001) were investigated by temp. programmed desorption (TPD) and IR reflection absorption spectroscopy (IRAS). The data reveal distinct modifications in the H adsorption behavior and also in the CO adsorption properties compared to adsorption of the individual components both on the monometallic and on the bimetallic surface. These modifications are discussed on an at. scale, in a picture that involves adsorbate-adsorbate interactions and site-specific variations in the (local) adsorption properties of the bimetallic surface, due to electronic ligand and strain effects and geometric ensemble effects.
- 44Wang, X.; Hong, Y.; Shi, H.; Szanyi, J. Kinetic Modeling and Transient DRIFTS–MS Studies of CO2 Methanation over Ru/Al2O3 Catalysts. J. Catal. 2016, 343, 185– 195, DOI: 10.1016/j.jcat.2016.02.00144https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xjt1Wltr0%253D&md5=e8f7695dde61aaa9a5fd16a98080faacKinetic modeling and transient DRIFTS-MS studies of CO2 methanation over Ru/Al2O3 catalystsWang, Xiang; Hong, Yongchun; Shi, Hui; Szanyi, JanosJournal of Catalysis (2016), 343 (), 185-195CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)CO2 methanation was investigated on 5% and 0.5% Ru/Al2O3 catalysts (Ru dispersions: ∼18% and ∼40%, resp.) by steady-state kinetic measurements and transient DRIFTS-MS. Methanation rates were higher over 5% Ru/Al2O3 than over 0.5% Ru/Al2O3. The measured activation energies, however, were lower on 0.5% Ru/Al2O3 than on 5% Ru/Al2O3. Transient DRIFTS-MS results demonstrated that direct CO2 dissocn. was negligible over Ru. CO2 has to first react with surface hydroxyls on Al2O3 to form bicarbonates, which, in turn, react with adsorbed H on Ru to produce adsorbed formate species. Formates, most likely at the metal/oxide interface, can react rapidly with adsorbed H forming adsorbed CO, only a portion of which is reactive toward adsorbed H, ultimately leading to CH4 formation. The unreactive CO mols. are in geminal form adsorbed on low-coordinated sites. The measured kinetics are fully consistent with a Langmuir-Hinshelwood type mechanism in which the H-assisted dissocn. of the reactive CO* is the rate-detg. step (RDS). The similar empirical rate expressions (rCH4 = kP0.1CO2P0.3-0.5H2) and DRIFTS-MS results on the two catalysts under both transient and steady-state conditions suggest that the mechanism for CO2 methanation does not change with Ru particle size under the studied exptl. conditions. Kinetic modeling results further indicate that the intrinsic activation barrier for the RDS is slightly lower on 0.5% Ru/Al2O3 than on 5% Ru/Al2O3. Due to the presence of unreactive adsorbed CO on low-coordinated Ru sites under reaction conditions, the larger fraction of such surface sites on 0.5% Ru/Al2O3 than on 5% Ru/Al2O3 is regarded as the main reason for the lower rates for CO2 methanation on 0.5% Ru/Al2O3.
- 45Cant, N. W.; Bell, A. T. Studies of Carbon Monoxide Hydrogenation over Ruthenium Using Transient Response Techniques. J. Catal. 1982, 73, 257– 271, DOI: 10.1016/0021-9517(82)90099-945https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XhtlSntLY%253D&md5=0477ea3f8c65fcd985d6aab1111471a0Studies of carbon monoxide hydrogenation over ruthenium using transient response techniquesCant, Noel W.; Bell, Alexis T.Journal of Catalysis (1982), 73 (2), 257-71CODEN: JCTLA5; ISSN:0021-9517.Transient response isotopic tracing was used together with in situ IR spectroscopy to elucidate the dynamics of several elementary processes believed to occur during CO hydrogenation over Ru catalysts. Chemisorbed CO exchanged rapidly with gas phase CO and under reaction conditions the 2 species were in equil. A similar conclusion was reached regarding the relation between gas phase H2 and adsorbed H atoms. The dissocn. of molecularly adsorbed CO to form at. C and O required vacant surface sites and was reversible. While CO is the principal adsorbed species present on the catalyst surface under reaction conditions, the catalyst also maintains a significant inventory of nonoxygenated C but no chemisorbed O. The rate at which nonoxygenated C undergoes hydrogenation is faster than the rate at which adsorbed CO is hydrogenated. This observation supports the hypothesis that the nonoxygenated C is an intermediate in CO hydrogenation.
- 46Carballo, J. M. G.; Finocchio, E.; García-Rodriguez, S.; Ojeda, M.; Fierro, J. L. G.; Busca, G.; Rojas, S. Insights into the Deactivation and Reactivation of Ru/TiO2 During Fischer–Tropsch Synthesis. Catal. Today 2013, 214, 2– 11, DOI: 10.1016/j.cattod.2012.09.01846https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1aqsbjJ&md5=48629d46077f3abfd0b0050cbcd49bc2Insights into the deactivation and reactivation of Ru/TiO2 during Fischer-Tropsch synthesisCarballo, Juan Maria Gonzalez; Finocchio, Elisabetta; Garcia-Rodriguez, Sergio; Ojeda, Manuel; Fierro, Jose Luis Garcia; Busca, Guido; Rojas, SergioCatalysis Today (2013), 214 (), 2-11CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)The catalytic performance of Ru/TiO2 for the prodn. of hydrocarbons via Fischer-Tropsch synthesis (FTS) was evaluated in this work. Ru/TiO2 exhibits high CO conversion rates (523 K, 2.5 MPa H2, 1.25 MPa CO) that decrease significantly with time-onstream. To recover the initial catalytic performance, different treatments using H2 or air were tested. The evolution of the catalyst structure during FTS and after the re-activation protocols were explored by a combination of ex situ and in situ techniques. Ru agglomeration, oxidn., and formation of Ru-volatile species are not responsible for the obsd. deactivation. However, Raman and IR (FTIR) spectroscopy have confirmed the presence of coke and alkyl chains on the spent catalysts. These species hinder the adsorption of the reactants on the active sites and are the primary reason for the obsd. decrease in the catalytic activity. These carbonaceous species can be removed by severe thermal treatments in air. However, this latter treatment drastically alters the morphol. of the Ru/TiO2, which leads to a substantial loss of catalytic activity.
- 47Saoud, W. A.; Assadi, A. A.; Guiza, M.; Bouzaza, A.; Aboussaoud, W.; Ouederni, A.; Soutrel, I.; Wolbert, D.; Rtimi, S. Study of Synergetic Effect, Catalytic Poisoning and Regeneration Using Dielectric Barrier Discharge and Photocatalysis in a Continuous Reactor: Abatement of Pollutants in Air Mixture System. Appl. Catal., B 2017, 213, 53– 61, DOI: 10.1016/j.apcatb.2017.05.012There is no corresponding record for this reference.
- 48Aziz, M. A. A.; Jalil, A. A.; Triwahyono, S.; Saad, M. W. A. CO2 Methanation over Ni-Promoted Mesostructured Silica Nanoparticles: Influence of Ni Loading and Water Vapor on Activity and Response Surface Methodology Studies. Chem. Eng. J. 2015, 260, 757– 764, DOI: 10.1016/j.cej.2014.09.03148https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFOqsb3I&md5=d344ec260a7602fdbe7c65a6753eec69CO2 methanation over Ni-promoted mesostructured silica nanoparticles: Influence of Ni loading and water vapor on activity and response surface methodology studiesAziz, M. A. A.; Jalil, A. A.; Triwahyono, S.; Saad, M. W. A.Chemical Engineering Journal (Amsterdam, Netherlands) (2015), 260 (), 757-764CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)The effects of Ni loading and H2O vapor on the properties of Ni/mesoporous SiO2 nanoparticles (MSN) and CO2 methanation were studied. X-ray diffraction, N2 adsorption-desorption, and pyrrole-adsorbed IR spectroscopy results indicated that the increasing Ni loading (1-10%) decreased the crystallinity, surface area, and basic sites of the catalysts. The activity of CO2 methanation followed the order of 10Ni/MSN ≈ 5Ni/MSN > 3Ni/MSN > 1Ni/MSN. The balance between Ni and the basic-site concn. is vital for the high activity of CO2 methanation. All Ni/MSN catalysts exhibited a high stability at 623 K for >100 h. The presence of H2O vapor in the feed stream induced a neg. effect on the activity of CO2 methanation. The H2O vapor decreased the carbonyl species concn. on the surface of Ni/MSN, as evidenced by CO + H2O-adsorbed IR spectroscopy. The response surface methodol. expts. were designed with face-centered central composite design (FCCCD) by applying 24 factorial points, 8 axial points, and 2 replicates, with one response variable (CO2 conversion). The Pareto chart indicated that the reaction temp. had the largest effect for all responses. The optimum CO2 conversion was predicted from the response surface anal. as 85% at an operating treatment time of 6 h, reaction temp. of 614 K, gas hourly space velocity (GHSV) of 69105 mL g-1cat h-1, and H2/CO2 ratio of 3.68.
- 49Falbo, L.; Martinelli, M.; Visconti, C. G.; Lietti, L.; Bassano, C.; Deiana, P. Kinetics of CO2 Methanation on a Ru-Based Catalyst at Process Conditions Relevant for Power-to-Gas Applications. Appl. Catal., B 2018, 225, 354– 363, DOI: 10.1016/j.apcatb.2017.11.06649https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFKmtL7P&md5=c379ca032bd0d3fcb35f2f3eefbe9516Kinetics of CO2 methanation on a Ru-based catalyst at process conditions relevant for Power-to-Gas applicationsFalbo, Leonardo; Martinelli, Michela; Visconti, Carlo Giorgio; Lietti, Luca; Bassano, Claudia; Deiana, PaoloApplied Catalysis, B: Environmental (2018), 225 (), 354-363CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)A 0.5% Ru/γ-Al2O3 catalyst is appropriate to carry out the Sabatier reaction (CO2 methanation) under process conditions relevant for the Power-to-Gas application and the authors provide a kinetic model able to describe the CO2 conversion over a wide range of process conditions, previously unexplored. To achieve these goals, the effects of feed gas compn. (H2/CO2 ratio and presence of diluents), space velocity, temp. and pressure on catalyst activity and selectivity are studied. The catalyst is found stable when operating over a wide range of CO2 conversion values, with CH4 selectivity always over 99% and no deactivation, even when working with C-rich gas streams. The effect of H2O on the catalyst performance is also studied and an inhibiting kinetic effect is pointed out. Eventually, the capacity of kinetic models taken from the literature to account for CO2 conversion under the explored exptl. conditions is assessed. The kinetic model proposed by Lunde and Kester in 1973 (J. Catal. 30(1973) 423) is able to describe satisfactorily the catalyst behavior in a wide range of CO2 conversion spanning from differential conditions to thermodn. equil., provided that a new set of kinetic parameters is used. However a better fitting can be achieved by using a modified kinetic model, accounting for the inhibiting effect of H2O on CO2 conversion rate.
- 50Bacariza, M. C.; Biset-Peiró, M.; Graça, I.; Guilera, J.; Morante, J.; Lopes, J. M.; Andreu, T.; Henriques, C. DBD Plasma-Assisted CO2 Methanation Using Zeolite-Based Catalysts: Structure Composition-Reactivity Approach and Effect of Ce as Promoter. J. CO2 Util. 2018, 26, 202– 211, DOI: 10.1016/j.jcou.2018.05.01350https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpslOmurc%253D&md5=d126cf04757760c27a2f384f34136f9fDBD plasma-assisted CO2 methanation using zeolite-based catalysts: Structure composition-reactivity approach and effect of Ce as promoterBacariza, M. C.; Biset-Peiro, M.; Graca, I.; Guilera, J.; Morante, J.; Lopes, J. M.; Andreu, T.; Henriques, C.Journal of CO2 Utilization (2018), 26 (), 202-211CODEN: JCUOAJ; ISSN:2212-9839. (Elsevier Ltd.)In the present work the effects of the structure compn. in terms of Si/Al ratio and Ce addn. in the performances of Ni-based zeolites for CO2 methanation under DBD plasma-assisted catalysis were evaluated. Results were compared with the obtained for a com. Ni/γ-Al2O3 catalyst and all samples were tested both under thermal and non-thermal DBD plasma conditions. It was found that a higher Si/Al ratio led to better performances not only under thermal but, esp., under plasma conditions, which was attributed to the lower affinity of this sample to water and, thus, to a decrease in the inhibitory role of this compd. in Sabatier reaction. Furthermore, the addn. of Ce as promoter favored the dielec. properties of the materials and gave addnl. sites for CO2 activation leading to much better results than the obtained for a com. Ni/γ-Al2O3 sample and for the Ni/zeolite, esp. under plasma conditions. Indeed, the best zeolite of this work (NiCe/Zeolite) reported a CH4 yield of 75% with a power supply of 25W while, under the same conditions, the com. sample and the un-promoted Ni/Zeolite presented just 23% and 15%, CH4 yield, resp. To our knowledge, this is the first time that a structure-reactivity relationship is attempted with zeolite catalysts under DBD plasma-assisted methanation conditions at atm. pressure. These facts also indicate that an important route is being opened, allowing answering to the essential question "what are the important characteristics a catalyst must have to show a better performance under plasma-assisted catalysis".
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscatal.0c03620.
Detailed characterization of catalysts; relevant catalyst assessment for catalytic CO2 hydrogenation; kinetic parameters of the thermal and NTP systems; relevant in situ DRIFTS data of the thermal and NTP-catalysis systems (PDF)
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