Hydrogenated Borophene Shows Catalytic Activity as Solid Acid
- Asahi FujinoAsahi FujinoGraduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Asahi Fujino,
- Shin-ichi ItoShin-ichi ItoDepartment of Materials Science, Faculty of Pure and Applied Sciences, , University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanMaterials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, JapanMore by Shin-ichi Ito,
- Taiga GotoTaiga GotoGraduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Taiga Goto,
- Ryota IshibikiRyota IshibikiGraduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Ryota Ishibiki,
- Junko N. KondoJunko N. KondoInstitute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, Kanagawa 226-8503, JapanMore by Junko N. Kondo,
- Tadahiro FujitaniTadahiro FujitaniDepartment of Materials Science, Faculty of Pure and Applied Sciences, , University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanInterdisciplinary Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, JapanMore by Tadahiro Fujitani,
- Junji NakamuraJunji NakamuraDepartment of Materials Science, Faculty of Pure and Applied Sciences, Tsukuba Research Center for Energy Materials Science, , University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Junji Nakamura,
- Hideo HosonoHideo HosonoMaterials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, JapanMore by Hideo Hosono, and
- Takahiro Kondo*Takahiro Kondo*E-mail: [email protected]Department of Materials Science, Faculty of Pure and Applied Sciences, Tsukuba Research Center for Energy Materials Science, , University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, JapanMaterials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, JapanMore by Takahiro Kondo
Copyright © 2019 American Chemical Society
Abstract
Hydrogen boride (HB) or hydrogenated borophene sheets are recently realized two-dimensional materials that are composed of only two light elements, boron and hydrogen. However, their catalytic activity has not been experimentally analyzed. Herein, we report the catalytic activity of HB sheets in ethanol reforming. HB sheets catalyze the conversion of ethanol to ethylene and water above 493 K with high selectivity, independent of the contact time, and with an apparent activation energy of 102.8 ± 5.5 kJ/mol. Hence, we identify that HB sheets act as solid-acid catalysts.
Note
This paper published ASAP on August 15, 2019 with an inaccurate equation due to production error. The corrected version reposted to the Web on August 19, 2019.
Introduction
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Two-dimensional (2D) materials have great potential for application as catalysts because of their unique properties such as large surface areas and novel electronic states.(1,2) Among 2D materials, boron-related materials have unique characteristics different from other 2D materials in that they have polymorphisms,(3−5) i.e., there are a wide variety of stable 2D phases owing to the capability to form multicenter bonding configurations of boron.(6) Single monoatomic 2D boron (borophene) layers have been fabricated on solid surfaces with several different stable structures,(7) which is consistent with theoretical predictions regarding polymorphs of borophene.(8−10)
These polymorph characteristics of 2D boron sheets provide an opportunity to optimize the catalytic performance by tuning the bonding configurations of the 2D boron network. For example, it has been recently reported that boron nanosheets exfoliated from bulk boron exhibited efficient electrocatalytic performance for NH3 formation from N2 in neutral media.(11) Recent experimental and theoretical studies also showed that α-phase molybdenum diboride (α-MoB2) comprising noble metal-free borophene subunits exhibits superefficient electrocatalytic properties for the hydrogen evolution reaction.(12) What we expect here is that these observed catalytic performances will be further improved by optimizing the electronic structure of 2D boron sheets through the adjusting of the 2D boron bonding-network configurations as well as conventional doping and/or composite formation.
This catalyst design concept with an attractive polymorph 2D boron character can be extended to hydrogenated borophene (referred to as borophane) sheets, since the polymorph 2D phases of borophane have been theoretically predicted.(5) However, the catalytic performance of borophane has not been experimentally analyzed, to the best of our knowledge.
Recently, we revealed that a type of borophane sheet, the hydrogen boride (HB) sheet, with an empirical formula of H1B1, can be experimentally prepared by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2), with an average yield of 42.3% at room temperature.(13) Our extensive analysis revealed that the prepared HB sheets did not show any long-range order but have a local structure of a hexagonal boron network with bridge hydrogens, as shown in Figure 1a.(13) A recent analysis using soft X-ray absorption and emission spectroscopy at the B K-shell also supports this view and shows the semimetallicity of HB sheets.(14) HB sheets release their hydrogen content as H2 molecules in a wide temperature range from 423 to 1473 K.(13) The hydrogen in HB has a character of protons (H+) rather than that of hydrides (H–), based on the B 1s core-level states, density functional theory calculations, and the Hammett acidity function (H0, acid strength); the H0 of HB sheets is below 1.5 and above 0.43.(13) From this viewpoint, we can regard HB sheets as proton-covered 2D boron sheets. We can thus expect that HB sheets would exhibit intriguing catalytic performance for proton-related chemical reactions and would be used as theoretically predicted hydrogen-storage materials(15,16) and in batteries.(17−19) In this work, we therefore examined the catalytic activity of HB sheets in the ethanol-reforming reaction to clarify their acid/base catalytic property and performance.
Figure 1
Figure 1. (a) Photograph of HB sheets in powder form and schematic of the proposed local structure.(13) (b) Conversion of ethanol vs temperature. The results for HB, B2O3, and MgB2 are plotted for various W/F (g·min/mmol) conditions (contact time, weight of the catalyst divided by the flow rate of C2H5OH).
Results and Discussion
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Figure 1b shows the conversion of ethanol as a function of temperature at various W/F conditions (contact time); W/F (g·min/mmol) is the weight of the catalyst (g) divided by the flow rate of C2H5OH (mmol/min). The conversion was estimated from the total amount of hydrocarbons in the product (see the details in the Supporting Information). In every case, we heated the sample at 573 K under Ar flow for 1 h prior to the measurement. It is clear that HB sheets exhibit distinct ethanol conversion, whereas MgB2 (starting material for the synthesis of HB) and B2O3 (product obtained by heating B(OH)3, which is a byproduct in HB sheet synthesis, to 400 K or more) exhibit no ethanol conversion. The conversion by the HB sheets increases with an increase in W/F; it is 90% at 573 K and W/F = 27.2 g·min/mmol. The conversion remains constant for a long period. As an example, the conversion at 573 K and W/F = 7.3 g·min/mmol as a function of the reaction time is shown by blue circles in Figure 2a. In this case, the total amount of hydrocarbons at 13.4 h is 3.2 mmol, which is approximately half of the total B atom numbers of used HB sheets. We also estimated the conversion from the ethanol consumption, as shown by the red triangles in Figure 2a (see the details in the Supporting Information). The conversion calculated from the hydrocarbon production and that from the ethanol consumption are almost the same at 12 h (approximately 40%), indicating that the product hydrocarbon does not accumulate on the catalyst HB sheets during the steady-state catalytic process. These results hence indicate that the HB sheets catalytically convert ethanol. It is notable that pretreatment heating at 573 K causes inevitable hydrogen release from HB as H2.(13) The maximum amount of released hydrogen at 573 K could be estimated as approximately 33–50 atom % of HB based on the thermal desorption spectroscopy (TDS) results(13) (see the details in the Supporting Information). It is implying that the stoichiometry of the HB sheets showing the catalytic activity was not H:B = 1:1 but approximately H:B = 1:2.5 ± 0.5 (if they were forming a uniform structure).
Figure 2
Figure 2. (a) Conversion of ethanol on HB sheets as a function of reaction time at 573 K and W/F = 7.3 g·min/mmol, estimated from hydrocarbon production (blue circles) and ethanol consumption (red triangles). (b) Selectivity vs reaction time.
We detected the catalytically converted products using gas chromatography; they were predominantly ethylene and water, together with other products such as methane, ethane, and a trace amount of acetaldehyde, as shown in Figure 2b. The selectivity of ethylene was relatively low at the early stage, i.e., 0–4 h reaction time; this could be ascribed to the presence of surplus hydrogen in HB compared with the amount of hydrogen at the steady-state in HB at 573 K (details in the Supporting Information). We observed the same characteristics at all of the measured temperatures and W/F conditions, as shown in Figure 3a,b; i.e., C2H4 was always the main product, and the selectivity for the obtained total hydrocarbon was almost the same. These results indicate that the major catalytic reaction of ethanol reforming by the HB sheets is the dehydration reaction: C2H5OH → C2H4 + H2O. It is known that if a catalyst promotes the dehydration reaction of ethanol, it is a solid-acid; however, if the dehydrogenation reaction occurs, producing an acetaldehyde, the catalyst is a base catalyst. The HB sheets are therefore solid-acid catalysts, which is consistent with the H0 of the HB sheets (below 1.5 and above 0.43)(13) in terms of the acidic character.
Figure 3
Figure 3. (a) Selectivity of ethanol reforming by HB as a function of temperature at W/F = 6.7 g·min/mmol. (b) Selectivity of ethanol reforming by HB at 573 K and W/F = 6.7, 13.6, and 27.2 g·min/mmol.
Figure 4 shows the Arrhenius plot of the ethanol-reforming reaction rate k, which was calculated by assuming a first-order reaction, as k = (C2H5OH conversion [%])/100 × (C2H5OH flux [mol/s])/(HB amount [mol]), for the results under various W/F conditions with the HB sheets. As the obtained linear lines are almost the same and they are independent of W/F, the reaction can be (at least apparently) considered a first-order reaction. To determine the exact reaction order and mechanism, further kinetic analysis is required. From the slope and the section, the apparent activation energy Ea and pre-exponential factor A were estimated to be 102.8 ± 5.5 kJ/mol and 3.5 × 104 s–1, respectively. The derived Ea is comparable to the reported activation energies for the catalytic dehydration of ethanol over Al2O3 (53–155 kJ/mol),(20,21) the Lewis acidic Zr-KIT-6 catalyst (79 kJ/mol),(22) silica–alumina (125.5 kJ/mol),(23) and microporous Fe-ZSM-5 (137.7–271.1 kJ/mol).(24) The formation rate of ethylene on our HB catalyst at 573 K and W/F = 7.3 g·min/mmol was 2.4 ± 0.1 mmol/g·h (Figure 2). Although this is not the formation rate at the optimal catalytic condition, here, we compare it with those of the other reported catalysts. Chen and co-workers reported that the formation rate of ethylene from ethanol using the commercial SynDol (Al2O3–MgO/SiO2) catalyst was 7.8 mmol/g·h at 591 K, with a weight hourly space velocity (WHSV) of 0.23 h–1 in a fixed-bed reactor (this value is calculated using the reported yield of the ethylene, which is 0.22 g/gcat·h).(25) They also reported a higher formation rate of 535 mmol/g·h on Ti/γ-Al2O3 at 633 K and WHSV of 26 h–1 using the microreactor (calculated using a value of 15 g/gcat·h).(25) The formation rate of HB sheets is, thus, lower than that of the state-of-the-art catalysts but is in the same order as that of the commercial SynDol catalyst.
Figure 4
Figure 4. Arrhenius plot of the ethanol-reforming reaction rate (k) in the presence of HB sheets for W/F = 27.2, 13.6, and 6.7 g·min/mmol.
Finally, we herein discuss the possible reaction mechanism and active sites as well as the acid property of the HB sheets. In the case of ethanol reforming on a zeolite catalyst,(26−32) diethyl ether (C2H5OC2H5) is formed as a result of a two-molecule reaction. Diethyl ether then converts to ethylene at strong Brønsted acid sites. The number and the strength of strong Brønsted acid sites in the catalyst are thus reported to determine the catalytic activity for ethylene formation. Since HB sheets show weaker H0 (1.5 ≥ H0 ≥ 0.43)(13) compared with that of zeolites (e.g., −3.0 ≥ H0 ≥ −8.2 of H-Zeolite),(33) we can expect the formation of diethyl ether rather than ethylene on HB sheets, based on the trend of zeolite. However, we observed ethylene instead of diethyl ether on the HB sheets (Figures 2 and 3). Thus, the reaction is considered to proceed as a single molecule reaction via the formation of an ethoxy (C2H5O−) species rather than the two-molecule reaction via the formation of diethyl ether. Indeed, the derived apparent activation energy (102.8 ± 5.5 kJ/mol) from Figure 4 is similar to that for the decomposition of the ethoxy intermediate generated from ethanol on a zeolite (122 ± 3 kJ/mol).(34) The ethoxy species can thus be formed prior to ethylene on HB; this will be investigated using infrared spectroscopy in our future work. Concerning the active site, the bridge-type hydrogen in the HB sheets and/or terminal-type hydrogen at the edge of the HB sheets can be expected to act as the Brønsted acid sites. However, as described above, the stoichiometry of the HB sheets used in this work for the catalytic activity measurements is not H:B = 1:1 due to the inevitable hydrogen release as H2 at the pretreatment heating of 573 K (release as much as 33–50% of hydrogen in HB). Thus, we cannot simply assign the hydrogen atoms of the outermost surface (bridge- and/or edge-type of hydrogens) of HB (Figure 1a) as the active sites. There is a possibility that the boron atom that does not bond with hydrogen acts as the Lewis acid site if a hydrogen vacancy is created locally and the boron atom adopts a simple sp2 bonding configuration with surrounding boron atoms (Figure 1a) without any electron in its pz orbital. On the other hand, if the charges in the HB sheets are delocalized well to supply electrons to the pz orbital of a bare sp2-bonded boron atom (at hydrogen vacancy), the boron atom may act as a Brønsted base, similar to the lattice oxygen in zeolite, and promote the dehydrogenation of ethoxy to form ethylene. According to our catalytic activity measurements for the HB sheets without pretreatment heating (Figure S4), the selectivity is different from that shown in Figure 3. This difference in selectivity can be attributed to the difference in the hydrogen amount in HB, as in the case of the origin of the induction period shown in Figure 2b (see the details in the Supporting Information). We can hence at least classify that the HB and heated HB (hydrogen-deficient-HB) have different catalytic properties (i.e., different acid sites). However, the active sites cannot be solely determined by our current experimental results. At least it should be clarified whether the hydrogen-deficient HB consists of a uniform stoichiometric structure or defective structure. Further investigation is thus required to determine the exact active sites of the HB solid-acid catalyst, e.g., the careful structure characterization, infrared spectroscopy analysis with pyridine, NH3, and CO2 adsorption, and H0 measurements with quantitative density, as a function of the pretreatment heating temperature (i.e., hydrogen amount in HB).
Conclusions
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We found that hydrogen boride or hydrogenated borophene sheets catalyze the conversion of ethanol to ethylene and water above 493 K, with high selectivity, independent of the contact time, and an apparent activation energy of 102.8 ± 5.5 kJ/mol. We hence consider hydrogenated borophene sheets to be novel, nonmetal, and two-dimensional solid-acid catalysts that have great potential for application as hydrogen-storage materials and in batteries.
Experimental Section
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Materials
HB sheets were prepared using a previously reported ion-exchange method.(13) Specifically, MgB2 powder (1.0 g, 99%, Rare Metallic Co., Ltd., Tokyo, Japan) in acetonitrile (300 mL, 99.5%, Wako Pure Chemical Industries Ltd., Osaka, Japan) was mixed with a solution of an ion-exchange resin (60 mL, Amberlite IR120B hydrogen form, Organo Corp., Tokyo, Japan) and acetonitrile (200 mL) in a Schlenk flask under a nitrogen atmosphere, where water inclusion is sensitive to the product(35) and thus careful removal of water was done beforehand. This mixture was stirred using a magnetic stirrer at 400 rpm for 2 days at room temperature. The supernatant was then kept for 1 day at 255 K to physically separate the byproduct B(OH)3. Dried HB sheets were prepared by heating the resulting liquid at 343 K while pumping with a liquid nitrogen trap. For all of the syntheses, we carefully confirmed the product by X-ray photoelectron spectroscopy to confirm the absence of Mg and the presence of negatively charged B without oxidized B as reported previously.(13) Moreover, we recently confirmed using atomic force microscopy (AFM) that our HB sheets mostly consist of a few to several tens of layers. The details of AFM with statistical analysis will be published in our future work.
Catalytic Activity Measurements
To determine the catalytic activity, gaseous ethanol was introduced into the HB sheets using an argon carrier gas under atmospheric pressure in a homemade fixed-bed flow reactor. The product gas was then analyzed using a thermal conductivity detector in a gas chromatograph (GC-8A, Shimadzu, Kyoto, Japan) equipped with Molecular Sieve 5A and Porapak Q at the downstream end of the reactor. The catalytic conversion was estimated from the total amount of hydrocarbon production using the following relation
As shown in Figure 2a, the conversion was also estimated from ethanol consumption as follows
The selectivity was estimated using the following relation
The catalytic activity was determined under various W/F conditions (g·min/mmol), which is the weight of the catalyst (g) divided by the flow rate of C2H5OH (mmol/min); W/F was controlled by adjusting the flow rate of C2H5OH and the weight of the sample. The W/F conditions used in this work are listed in Table S1.
As shown in Figure 2a, the conversion was also estimated from ethanol consumption as followsThe selectivity was estimated using the following relationThe catalytic activity was determined under various W/F conditions (g·min/mmol), which is the weight of the catalyst (g) divided by the flow rate of C2H5OH (mmol/min); W/F was controlled by adjusting the flow rate of C2H5OH and the weight of the sample. The W/F conditions used in this work are listed in Table S1.ARTICLE SECTIONS
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b02020.
Origin of the induction period, TDS, effect of water, and catalytic activity of HB without pretreatment heating (PDF)
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Author Information
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- Takahiro Kondo - Department of Materials Science, Faculty of Pure and Applied Sciences, Tsukuba Research Center for Energy Materials Science, , , and , University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan; Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan;
http://orcid.org/0000-0001-8457-9387;
- Junko N. Kondo - Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, Kanagawa 226-8503, Japan;http://orcid.org/0000-0002-7940-1266
- Tadahiro Fujitani - Department of Materials Science, Faculty of Pure and Applied Sciences, , , and , University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan; Interdisciplinary Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan;http://orcid.org/0000-0002-1225-3246
- Hideo Hosono - Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan;http://orcid.org/0000-0001-9260-6728
The authors declare no competing financial interest.
Acknowledgments
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This work was supported by the JSPS KAKENHI nos. JP 18K18989, JP 19H05046, and JP 19H02551 and Murata Science Foundation, KUMAGAI, Ogasawara, and Samco foundations for the Promotion of Science & Engineering. T.K., S.-i.I., and H.H. were supported by the MEXT Element Strategy Initiative to Form Core Research Center.
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- 8Boustani, I. New Quasi-Planar Surfaces of Bare Boron. Surf. Sci. 1997, 370, 355– 363, DOI: 10.1016/S0039-6028(96)00969-7[Crossref], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXmsFCnsQ%253D%253D&md5=18c3da11837f6386092928972508ca6cNew quasi-planar surfaces of bare boronBoustani, IhsanSurface Science (1997), 370 (2-3), 355-363CODEN: SUSCAS; ISSN:0039-6028. (Elsevier)New very stable quasi-planar clusters of bare boron are found by systematic ab initio d. functional and quantum chem. methods. They are composed of dove-tailed hexagonal pyramids different from the classical forms of α- or β-rhombohedral boron crystallines. The quasi-planar structures are considered to be fragments of quasi-planar surfaces, which can easily be obtained and constructed from a basic unit of hexagonal pyramids. A new investigation on double layers of boron quasi-planar surfaces shows an increase in the stability of the system which can be related to the overlap of .vpi.-orbitals between the layers. Therefore, we predict the existence of a series of parallel boron layers, as in graphite. These proposed surfaces can serve as lightweight protective armor, as a neutron-absorber material in fission reactions, or as very high temp. semiconductors.
- 9Penev, E. S.; Bhowmick, S.; Sadrzadeh, A.; Yakobson, B. I. Polymorphism of Two-Dimensional Boron. Nano Lett. 2012, 12, 2441– 2445, DOI: 10.1021/nl3004754[ACS Full Text], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XlsVarsLY%253D&md5=2267c2e58b67aa9a8c5a6a198e0020c3Polymorphism of Two-Dimensional BoronPenev, Evgeni S.; Bhowmick, Somnath; Sadrzadeh, Arta; Yakobson, Boris I.Nano Letters (2012), 12 (5), 2441-2445CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The structural stability and diversity of elemental B layers are evaluated by treating them as pseudoalloy B1-x(vacancy)x, where x is a vacancy in the close-packed triangular B lattice. This approach allows for an elegant use of the cluster expansion method in combination with 1st-principles d.-functional theory calcns., leading to a thorough exploration of the configurational space. A finite range of compns. x is found where the ground-state energy is essentially independent of x, uncovering a variety of stable B-layer phases (all metallic) and suggesting polymorphism, in Stark contrast to graphene or hexagonal BN.
- 10Wu, X.; Dai, J.; Zhao, Y.; Zhuo, Z.; Yang, J.; Zeng, X. C. Two-Dimensional Boron Monolayer Sheets. ACS Nano 2012, 6, 7443– 7453, DOI: 10.1021/nn302696v[ACS Full Text], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtVKqurrK&md5=6428d25c89484b2b5a0da0ab56d7bbf0Two-Dimensional Boron Monolayer SheetsWu, Xiaojun; Dai, Jun; Zhao, Yu; Zhuo, Zhiwen; Yang, Jinlong; Zeng, Xiao ChengACS Nano (2012), 6 (8), 7443-7453CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Boron, a nearest-neighbor of carbon, is possibly the second element that can possess free-standing flat monolayer structures, evidenced by recent successful synthesis of single-walled and multiwalled boron nanotubes (MWBNTs). From an extensive structural search using the first-principles particle-swarm optimization (PSO) global algorithm, two boron monolayers (α1- and β1-sheet) are predicted to be the most stable α- and β-types of boron sheets, resp. Both boron sheets possess greater cohesive energies than the state-of-the-art two-dimensional boron structures (by more than 60 meV/atom based on d. functional theory calcn. using PBE0 hybrid functional), i.e., the α-sheet previously predicted by Tang and Ismail-Beigi and the g1/8- and g2/15-sheets (both belonging to the β-type) recently reported by Yakobson and co-workers. Moreover, the PBE0 calcn. predicts that the α-sheet is a semiconductor, while the α1-, β1-, g1/8-, and g2/15-sheets are all metals. When two α1 monolayers are stacked on top each other, the bilayer α1-sheet remains flat with an optimal interlayer distance of ∼3.62 Å, which is close to the measured interlayer distance (∼3.2 Å) in MWBNTs.
- 11Zhang, X.; Wu, T.; Wang, H.; Zhao, R.; Chen, H.; Wang, T.; Wei, P.; Luo, Y.; Zhang, Y.; Sun, X. Boron Nanosheet: An Elemental Two-Dimensional (2D) Material for Ambient Electrocatalytic N2 -to-NH3 Fixation in Neutral Media. ACS Catal. 2019, 9, 4609– 4615, DOI: 10.1021/acscatal.8b05134[ACS Full Text], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXnvFChtbk%253D&md5=7cfdf04f92fb1f02a920bc466a920589Boron Nanosheet: An Elemental Two-Dimensional (2D) Material for Ambient Electrocatalytic N2-to-NH3 Fixation in Neutral MediaZhang, Xiaoxue; Wu, Tongwei; Wang, Huanbo; Zhao, Runbo; Chen, Hongyu; Wang, Ting; Wei, Peipei; Luo, Yonglan; Zhang, Yanning; Sun, XupingACS Catalysis (2019), 9 (5), 4609-4615CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)The Haber-Bosch process for industrial NH3 prodn. suffers from harsh reaction conditions and serious CO2 emission. Electrochem. N2 redn. offers a C-neutral alternative for more energy-saving NH3 synthesis but requires active electrocatalysts for the N2 redn. reaction (NRR). In this Letter, B nanosheet (BNS) is proposed as an elemental two-dimensional (2D) material to effectively catalyze the NRR toward NH3 synthesis with excellent selectivity. When tested in 0.1M Na2SO4, such BNS catalyst attains a high faradaic efficiency of 4.04% and a large NH3 yield of 13.22 μg h-1 mgcat-1 at -0.80 V vs. reversible H electrode, with strong electrochem. durability. D. functional theory calcns. suggest that the B atoms of both oxidized and H-deactivated BNS can catalyze the NRR more effectively than clean BNS, and the rate-detg. step is the desorption process of the 2nd NH3 gas.
- 12Chen, Y.; Yu, G.; Chen, W.; Liu, Y.; Li, G.; Zhu, P.; Tao, Q.; Li, Q.; Liu, J.; Shen, X. Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2017, 139, 12370– 12373, DOI: 10.1021/jacs.7b06337[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFCju7bJ&md5=b3a29c5674c2b53c2522b2d4e8fd72a6Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution ReactionChen, Yanli; Yu, Guangtao; Chen, Wei; Liu, Yipu; Li, Guo-Dong; Zhu, Pinwen; Tao, Qiang; Li, Qiuju; Liu, Jingwei; Shen, Xiaopeng; Li, Hui; Huang, Xuri; Wang, Dejun; Asefa, Tewodros; Zou, XiaoxinJournal of the American Chemical Society (2017), 139 (36), 12370-12373CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Developing nonprecious hydrogen evolution electrocatalysts that can work well at large current densities (e.g., at 1000 mA/cm2: a value that is relevant for practical, large-scale applications) is of great importance for realizing a viable water-splitting technol. Herein we present a combined theor. and exptl. study that leads to the identification of α-phase molybdenum diboride (α-MoB2) comprising borophene subunits as a noble metal-free, superefficient electrocatalyst for the hydrogen evolution reaction (HER). Our theor. finding indicates, unlike the surfaces of Pt- and MoS2-based catalysts, those of α-MoB2 can maintain high catalytic activity for HER even at very high hydrogen coverage and attain a high d. of efficient catalytic active sites. Expts. confirm α-MoB2 can deliver large current densities in the order of 1000 mA/cm2, and also has excellent catalytic stability during HER. The theor. and exptl. results show α-MoB2's catalytic activity, esp. at large current densities, is due to its high cond., large d. of efficient catalytic active sites and good mass transport property.
- 13Nishino, H.; Fujita, T.; Cuong, N. T.; Tominaka, S.; Miyauchi, M.; Iimura, S.; Hirata, A.; Umezawa, N.; Okada, S.; Nishibori, E. Formation and Characterization of Hydrogen Boride Sheets Derived from MgB2 by Cation Exchange. J. Am. Chem. Soc. 2017, 139, 13761– 13769, DOI: 10.1021/jacs.7b06153[ACS Full Text], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFSrt7bJ&md5=8628d81604ddeeb0b6f5f403aacf1c73Formation and characterization of hydrogen boride sheets derived from MgB2 by cation exchangeNishino, Hiroaki; Fujita, Takeshi; Cuong, Nguyen Thanh; Tominaka, Satoshi; Miyauchi, Masahiro; Iimura, Soshi; Hirata, Akihiko; Umezawa, Naoto; Okada, Susumu; Nishibori, Eiji; Fujino, Asahi; Fujimori, Tomohiro; Ito, Shin-ichi; Nakamura, Junji; Hosono, Hideo; Kondo, TakahiroJournal of the American Chemical Society (2017), 139 (39), 13761-13769CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mech. properties as well as hydrogen storage capacity. Here, we report the exptl. realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an av. yield of 42.3% at room temp. The sheets feature an sp2-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray at. pair distribution functions, electron diffraction, transmission electron microscopy, photo absorption, core-level binding energy data, IR absorption, electron energy loss spectroscopy, and d. functional theory calcns. The established cation-exchange method for metal diboride opens new avenues for the mass prodn. of several types of boron-based 2D materials by countercation selection and functionalization.
- 14Tateishi, I.; Cuong, N. T.; Moura, C. A. S.; Cameau, M.; Ishibiki, R.; Fujino, A.; Okada, S.; Yamamoto, A.; Araki, M.; Ito, S. Semimetallicity of Free-Standing Hydrogenated Monolayer Boron from MgB2. Phys. Rev. Mater. 2019, 3, 024004 DOI: 10.1103/PhysRevMaterials.3.024004[Crossref], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGrsrnP&md5=2e5513892fc90333cd10b9b9df7c3758Semimetallicity of free-standing hydrogenated monolayer boron from MgB2Tateishi, I.; Cuong, N. T.; Moura, C. A. S.; Cameau, M.; Ishibiki, R.; Fujino, A.; Okada, S.; Yamamoto, A.; Araki, M.; Ito, S.; Yamamoto, S.; Niibe, M.; Tokushima, T.; Weibel, D. E.; Kondo, T.; Ogata, M.; Matsuda, I.Physical Review Materials (2019), 3 (2), 024004CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)Electronic states of a free-standing hydrogenated monolayer boron (HB) sheet were studied via soft x-ray spectroscopies at the B K-shell absorption edge and first-principles calcns. The HB sheet is semimetallic with electron and hole pockets at the Y and Γ points, resp. The electron band results from the B-H-B bonds formed during synthesis from a MgB2 crystal, while the hole band is kept through the process and originates from a honeycomb lattice boron layer or borophene in MgB2. Our results suggest that the HB sheet is a promising two-dimensional material for realizing new boron-based or superconducting nanodevices.
- 15Chen, L.; Chen, X.; Duan, C.; Huang, Y.; Zhang, Q.; Xiao, B. Reversible Hydrogen Storage in Pristine and Li Decorated 2D Boron Hydride. Phys. Chem. Chem. Phys. 2018, 20, 30304– 30311, DOI: 10.1039/C8CP05846F[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitF2qurbP&md5=cd8235d7cc5418e2b82a6099ad3caceeReversible hydrogen storage in pristine and Li decorated 2D boron hydrideChen, Long; Chen, Xianfei; Duan, Chao; Huang, Yi; Zhang, Qian; Xiao, BeibeiPhysical Chemistry Chemical Physics (2018), 20 (48), 30304-30311CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Motived by the recent exptl. fabrication of two-dimensional boron hydride (BH) sheets (Nishino et al., J. Am. Chem. Soc. 2017, 139, 13761), we explore the feasibility of pristine and Li doped BH sheets as a hydrogen storage medium within the framework of d. functional theory. BH shows an unexpected high affinity to Li with a binding energy of -2.38 eV in comparison to other alkali and alk. earth metals (Na, K, Ca, Mg and Al), much larger than its bulk cohesive energy (-1.63 eV). Energy barriers of Li diffusion on BH are also detd. to be around 1.12 eV, showing both high dynamic and thermodn. stability without the issue of cluster formation. Moreover, Li decorated BH is expected to achieve a high theor. gravimetric d. of 11.57 wt% with an av. H2 adsorption energy of -0.17 eV, holding great potential in massive hydrogen storage. In addn. to the storage, thermodn. anal. on the desorption behaviors of H2 mols. is performed via N-P-T diagram, which demonstrates that most of the H2 mols. (8.30 wt%) could be released at 3 atm/100 °C. Thus, the Li-decorated BH sheets are expected to be applied as an efficient medium for hydrogen storage under ambient conditions.
- 16Abtew, T. A.; Shih, B. C.; Dev, P.; Crespi, V. H.; Zhang, P. Prediction of a Multicenter-Bonded Solid Boron Hydride for Hydrogen Storage. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 094108 DOI: 10.1103/PhysRevB.83.094108[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXkt1GjsLg%253D&md5=d31d98946049414237ef1475b2c921c0Prediction of a multicenter-bonded solid boron hydride for hydrogen storageAbtew, Tesfaye A.; Shih, Bi-ching; Dev, Pratibha; Crespi, Vincent H.; Zhang, PeihongPhysical Review B: Condensed Matter and Materials Physics (2011), 83 (9), 094108/1-094108/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)A layered solid boron hydride structure (B2H2) consisting of a hexagonal boron network and bridge hydrogen which has a gravimetric capacity of 8 wt.% hydrogen is predicted. The structural, electronic, and dynamical properties of the proposed structure are investigated using first-principles electronic structure methods. The absence of soft phonon modes confirms the dynamical stability of the proposed structure. Charging the structure significantly softens hydrogen related phonon modes. Boron modes, in contrast, are either hardened or not significantly affected by electron doping. Furthermore, self-doping the structure considerably reduces the energy barrier against hydrogen release. These results suggest that electrochem. charging or self-doping mechanisms may facilitate hydrogen release while the underlying boron network remains intact for subsequent rehydrogenation.
- 17Makaremi, M.; Mortazavi, B.; Singh, C. V. 2D Hydrogenated Graphene-like Borophene as a High Capacity Anode Material for Improved Li/Na Ion Batteries: A First Principles Study. Mater. Today Energy 2018, 8, 22– 28, DOI: 10.1016/j.mtener.2018.02.003
- 18Xiang, P.; Chen, X.; Xiao, B.; Wang, Z. M. Highly Flexible Hydrogen Boride Monolayers as Potassium-Ion Battery Anodes for Wearable Electronics. ACS Appl. Mater. Interfaces 2019, 11, 8115– 8125, DOI: 10.1021/acsami.8b22214[ACS Full Text], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlChu78%253D&md5=106434c435c2774e3bc34acf2eb30d80Highly Flexible Hydrogen Boride Monolayers as Potassium-Ion Battery Anodes for Wearable ElectronicsXiang, Pan; Chen, Xianfei; Xiao, Beibei; Wang, Zhiming M.ACS Applied Materials & Interfaces (2019), 11 (8), 8115-8125CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)The rapid development of wearable electronics revealed an urgent need of low-cost, high-flexible, and high-capacity power sources. In this sense, emerging rechargeable K-ion batteries (KIBs) are promising candidate owing to their abundant resources, low-cost and lower redox potential in nonaq. electrolytes compared to Li-ion batteries. However, the fabrication of flexible KIBs remains highly challenging because of the lack of high-performance flexible electrode materials. The authors studied the mech. properties and electrochem. performance of recently developed H boride (BH) monolayer as a high-performance anode material based on d. functional theory (DFT) formalism. (i) BH presents ultra-low out-of-plane bending stiffness, rivaling that of graphene, which endows it with better flexibility to accommodate the repeat bending, rolling and folding on wearable device operation; (ii) high in-plane stiffness (157 N/m along armchair and 109 N/m along zigzag) in BH makes the electrode stable against pulverization upon external and internal strains. More importantly, BH electrode delivers low voltage of ∼0.24 eV in addn. to desired K-ion affinity and hopping resistance which remains very stable with the bending curvature. Emerged H vacancies in electrode improve both the K-ion intercalation and K-ion hopping, yielding a high theor. capacity (1138 mAh/g), which was among the highest reported values in the literature for K-ion anode materials. All the presented results suggested that a BH electrode could be used as a brand-new flexible and lightwt. KIB anode with high capacity, low voltage, and desired rate performance.
- 19Shukla, V.; Araujo, R. B.; Jena, N. K.; Ahuja, R. Borophene’s Tryst with Stability: Exploring 2D Hydrogen Boride as an Electrode for Rechargeable Batteries. Phys. Chem. Chem. Phys. 2018, 20, 22008– 22016, DOI: 10.1039/C8CP03686A[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsVWqt7zK&md5=464f61c13302f3a98f43c043a5e49093Borophene's tryst with stability: exploring 2D hydrogen boride as an electrode for rechargeable batteriesShukla, Vivekanand; Araujo, Rafael B.; Jena, Naresh K.; Ahuja, RajeevPhysical Chemistry Chemical Physics (2018), 20 (34), 22008-22016CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Graphene's emergence can be viewed as a pos. upheaval in 2D materials research. Along the same line, the realization of a related elemental 2D material, borophene, is another breakthrough. To circumvent the stability issues of borophene, which is reported to have been synthesized on metallic substrates under extreme conditions, hydrogenation of borophene (otherwise called as borophane or hydrogen boride or boron hydride) has been a plausible soln., but only proposed computationally. A recent report brings to fore its exptl. realization. Our current study delves into the possibilities of employing this intriguing 2D hydrogen boride as anodes in Li/Na ion batteries. Using first-principles d. functional theory methods, we computed relevant properties such as the ion (Li/Na) adsorption behavior, the possible pathways of ionic diffusion with the estn. of barriers as well as the theor. specific capacities and av. voltages to uniquely demonstrate that this material is of particular significance for battery applications. It is noted that the use of hydrogen boride leads to a high specific capacity of 861.78 mA h g-1 for Li ions, which is remarkably higher than the value reported in relation to its computationally predicted structure. Furthermore, Na ion intercalation leads to neg. voltage profiles, implying the unsuitability of 2D hydrogen boride for this particular ion. Our findings are timely and pertinent towards adding insightful details relevant to the progress of applications of 2D materials for energy storage.
- 20Bakoyannakis, D. N.; Zamboulis, D.; Stalidis, G. A.; Deliyanni, E. A. The Effect of Preparation Method on the Catalytic Activity of Amorphous Aluminas in Ethanol Dehydration. J. Chem. Technol. Biotechnol. 2001, 76, 1159– 1164, DOI: 10.1002/jctb.487[Crossref], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXotVSgtbc%253D&md5=c677a1f23f035b840e698033c68c6790The effect of preparation method on the catalytic activity of amorphous aluminas in ethanol dehydrationBakoyannakis, Demetris N.; Zamboulis, Demetris; Stalidis, George A.; Deliyanni, Eleni A.Journal of Chemical Technology & Biotechnology (2001), 76 (11), 1159-1164CODEN: JCTBED; ISSN:0268-2575. (John Wiley & Sons Ltd.)The known heterogeneous catalytic dehydration of ethanol on amorphous aluminum oxide samples was adopted as a measure of catalytic activity and selectivity. The aluminum oxide samples were prepd. by hydrolysis of aluminum chloride using propylamine, as proton acceptor, in pure and mixed aq. ethanolic and acetonic media, freeze dried and activated. The catalytic activity and selectivity of the samples was measured in the temp. range 623-698 K for various flow rates of ethanol. The apparent activation energies were calcd. (53-78 kJ mol-1) and depended on the solvent used in the prepn. of the aluminas. The effect of solvent medium on the activity and selectivity was discussed.
- 21Christiansen, M. A.; Mpourmpakis, G.; Vlachos, D. G. Density Functional Theory-Computed Mechanisms of Ethylene and Diethyl Ether Formation from Ethanol on γ-Al2O3(100). ACS Catal. 2013, 3, 1965– 1975, DOI: 10.1021/cs4002833[ACS Full Text], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtF2ru7nM&md5=377f38379dc750e27d3ecfc736b804b1Density Functional Theory-Computed Mechanisms of Ethylene and Diethyl Ether Formation from Ethanol on γ-Al2O3(100)Christiansen, Matthew A.; Mpourmpakis, Giannis; Vlachos, Dionisios G.ACS Catalysis (2013), 3 (9), 1965-1975CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Multiple potential active sites on the surface of γ-Al2O3 have led to debate about the role of Lewis and/or Bronsted acidity in reactions of ethanol, while mechanistic insights into competitive prodn. of ethylene and di-Et ether are scarce. In this study, elementary adsorption and reaction mechanisms for ethanol dehydration and etherification are studied on the γ-Al2O3(100) surface using d. functional theory calcns. The O atom of adsorbed ethanol interacts strongly with surface Al (Lewis acid) sites, while adsorption is weak on Bronsted (surface H) and surface O sites. Water, a byproduct of both ethylene and di-Et ether formation, competes with ethanol for adsorption sites. Multiple pathways for ethylene formation from ethanol are explored, and a concerted Lewis-catalyzed elimination (E2) mechanism is found to be the energetically preferred pathway, with a barrier of Ea = 37 kcal/mol at the most stable site. Di-Et ether formation mechanisms presented for the first time on γ-Al2O3 indicate that the most favorable pathways involve Lewis-catalyzed SN2 reactions (Ea = 35 kcal/mol). Addnl. novel mechanisms for di-Et ether decompn. to ethylene are reported. Bronsted-catalyzed mechanisms for ethylene and ether formation are not favorable on the (100) facet because of weak adsorption on Bronsted sites. These results explain multiple exptl. observations, including the competition between ethylene and di-Et ether formation on alumina surfaces.
- 22Pan, Q.; Ramanathan, A.; Kirk Snavely, W.; Chaudhari, R. V.; Subramaniam, B. Intrinsic Kinetics of Ethanol Dehydration over Lewis Acidic Ordered Mesoporous Silicate, Zr-KIT-6. Top. Catal. 2014, 57, 1407– 1411, DOI: 10.1007/s11244-014-0311-7[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVyrtr3M&md5=6e65781e3e82c8c3aae5c770d4512804Intrinsic Kinetics of Ethanol Dehydration Over Lewis Acidic Ordered Mesoporous Silicate, Zr-KIT-6Pan, Qing; Ramanathan, Anand; Kirk Snavely, W.; Chaudhari, Raghunath V.; Subramaniam, BalaTopics in Catalysis (2014), 57 (17-20), 1407-1411CODEN: TOCAFI; ISSN:1022-5528. (Springer)Lewis acidic Zr-KIT-6 catalyst was tested for ethanol dehydration. Under the reaction conditions studied (T = 300-380 °C, P = 1 atm, Pethanol = 5 % in N2), Zr-KIT-6 materials showed high ethylene selectivity (∼80 %) with stable activity (60 h). The activation energy for ethanol dehydration to ethylene, estd. from intrinsic rate consts. normalized with respect to the Lewis acid sites, was approx. 79 ± 1 kJ/mol.
- 23Roca, F.; De Mourgues, L.; Trambouze, Y. Catalytic Dehydration of Ethanol over Silica-Alumina. J. Catal. 1969, 14, 107– 113, DOI: 10.1016/0021-9517(69)90414-X
- 24Maihom, T.; Khongpracha, P.; Sirijaraensre, J.; Limtrakul, J. Mechanistic Studies on the Transformation of Ethanol into Ethene over Fe-ZSM-5 Zeolite. ChemPhysChem 2013, 14, 101– 107, DOI: 10.1002/cphc.201200786[Crossref], [PubMed], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslSmu7rF&md5=7572347b1aff7dd9f1d8ea3ca07bfa03Mechanistic Studies on the Transformation of Ethanol into Ethene over Fe-ZSM-5 ZeoliteMaihom, Thana; Khongpracha, Pipat; Sirijaraensre, Jakkapan; Limtrakul, JumrasChemPhysChem (2013), 14 (1), 101-107CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)Ethanol, through the utilization of bioethanol as a chem. resource, has received considerable industrial attention as it provides an alternative route to produce more valuable hydrocarbons. Using a d. functional theory approach incorporating the M06-L functional, which includes dispersion interactions, a large 34T nanocluster model of Fe-ZSM-5 zeolite in which T is a Si or Al atom is employed to examine both the stepwise and concerted mechanisms of the transformation of ethanol into ethene. For the stepwise mechanism, ethanol dehydration commences from the first hydrogen abstraction of the ethanol OH group to form the ethoxide-hydroxide intermediate with a low activation energy of 17.7 kcal mol-1. Consequently, the ethoxide-hydroxide intermediate is decompd. into ethene through hydrogen abstraction from the ethoxide Me carbon to either the OH group of hydroxide or the oxygen of the ethoxide group with high activation energies of 64.8 and 63.5 kcal mol-1, resp. For the concerted mechanism, ethanol transformation into the ethene product occurs in a single step without intermediate formation, with an activation energy of 32.9 kcal mol-1.
- 25Chen, G.; Li, S.; Jiao, F.; Yuan, Q. Catalytic Dehydration of Bioethanol to Ethylene over TiO2/γ-Al2O3 Catalysts in Microchannel Reactors. Catal. Today 2007, 125, 111– 119, DOI: 10.1016/j.cattod.2007.01.071[Crossref], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXntF2lu74%253D&md5=31270fbfc97e7b279f0169918ede04a3Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactorsChen, Guangwen; Li, Shulian; Jiao, Fengjun; Yuan, QuanCatalysis Today (2007), 125 (1-2), 111-119CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Ethylene prodn. via catalytic dehydration of ethanol over TiO2/γ-Al2O3 catalysts in multi-microchannel reactors is reported. The physicochem. properties of these catalysts are characterized by X-ray diffraction and FT-IR spectra. The effects of operation parameters, such as ethanol concn., reaction temp., and liq. hourly space velocity, have been investigated exptl. The reaction results indicate that the catalysts doped with TiO2 have high ethanol conversion of 99.96% and ethylene selectivity of 99.4%. An ethylene yield of 26 g/(gcat h) can be achieved, which provides a very favorable foundation for intensification and miniaturization of the ethylene prodn. process using bioethanol.
- 26Takahara, I.; Saito, M.; Inaba, M.; Murata, K. Dehydration of Ethanol into Ethylene over Solid Acid Catalysts. Catal. Lett. 2005, 105, 249– 252, DOI: 10.1007/s10562-005-8698-1[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1aiur7K&md5=6caff1aa6565ea48a550394573f48e0eDehydration of Ethanol into Ethylene over Solid Acid CatalystsTakahara, Isao; Saito, Masahiro; Inaba, Megumu; Murata, KazuhisaCatalysis Letters (2005), 105 (3-4), 249-252CODEN: CALEER; ISSN:1011-372X. (Springer)The dehydration of ethanol into ethylene was investigated over various solid acid catalysts, such as zeolites and silica-alumina, at temps. ranging 453-573 K under atm. pressure. Ethylene was produced via di-Et ether during the dehydration process. H-mordenites were the most active for the dehydration. The catalyst activity could be correlated with the no. of strong Bronsted acid sites in the catalyst. Further, the H-mordenite was more stable with a SiO2/Al2O3 ratio of 90 than with a SiO2/Al2O3 ratio of 20.
- 27Madeira, F. F.; Gnep, N. S.; Magnoux, P.; Maury, S.; Cadran, N. Ethanol Transformation over HFAU, HBEA and HMFI Zeolites Presenting Similar Brønsted Acidity. Appl. Catal., A 2009, 367, 39– 46, DOI: 10.1016/j.apcata.2009.07.033[Crossref], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFGjtrzK&md5=7306851ba940b78754841845ca239383Ethanol transformation over HFAU, HBEA and HMFI zeolites presenting similar Bronsted acidityMadeira, F. Ferreira; Gnep, N. S.; Magnoux, P.; Maury, S.; Cadran, N.Applied Catalysis, A: General (2009), 367 (1-2), 39-46CODEN: ACAGE4; ISSN:0926-860X. (Elsevier B.V.)Ethanol transformation into higher hydrocarbons in one step by heterogeneous acid catalysis was studied, at 350° and 30 bar total pressure. Three zeolites (HFAU, HBEA and HZSM-5) were compared, which have the same quantity of Bronsted acid sites but different pore architecture. Large pore HFAU and HBEA zeolites gave mainly increasing yield of ethylene and di-Et ether with time-onstream, due to deactivation of the strongest acid sites, and only small amts. of C3+ hydrocarbons. This was explained by a faster deactivation of large pore zeolites due to fast coke formation which rapidly eliminates strong Bronsted acid sites, required for the transformation of ethylene into higher hydrocarbons. The coke mols. were identified as polyarom. compds. Medium pore zeolite HZSM-5 showed an important formation of C3+ hydrocarbons (mostly C5-C11 compds.) and small amts. of ethylene and di-Et ether. For this zeolite, after 16 h reaction, there was still complete ethanol transformation into C3+ hydrocarbons, despite a 55% loss of microporosity and 94% loss of Bronsted acidity. On HZSM-5, the deactivation is slower and the formation of C3+ hydrocarbons was obsd. even when the catalyst was satd. with coke mols. (high activity for the hydrogen transfer reactions). It could be possible that for this zeolite, the reaction occurs at the edge of the pore channel.
- 28Chiang, H.; Bhan, A. Catalytic Consequences of Hydroxyl Group Location on the Rate and Mechanism of Parallel Dehydration Reactions of Ethanol over Acidic Zeolites. J. Catal. 2010, 271, 251– 261, DOI: 10.1016/j.jcat.2010.01.021[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXltF2ju78%253D&md5=5f29462c9882b15b00b8c6c0af4ded71Catalytic consequences of hydroxyl group location on the rate and mechanism of parallel dehydration reactions of ethanol over acidic zeolitesChiang, Hsu; Bhan, AdityaJournal of Catalysis (2010), 271 (2), 251-261CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)The effects of zeolite topol. on the dehydration of oxygen-contg. mols. were probed in steady-state and isotopic chem. reactions of ethanol over proton-form zeolite materials (FER, MFI and MOR) at low temps. (368-409 K). The measured rate of di-Et ether (DEE) synthesis was largely independent of ethanol partial pressure on all proton-form zeolites (FER, MFI, and MOR), indicating that DEE formation involves the activation of ethanol dimers. The measured rate of DEE synthesis over H-FER increased with increasing ethylene pressure in expts. done with ethanol-ethylene mixts., reflecting the weaker adsorption of ethanol dimers on the FER framework compared to that on MFI and MOR materials, thereby resulting in the co-adsorption and reaction of ethylene with ethanol on FER materials. Ethylene prodn. was only obsd. on H-MOR because the small eight-membered ring side pockets protect ethanol monomers from forming bulky ethanol dimers. Secondary kinetic isotopic effects measured for ethylene synthesis rates using C2D5OD and C2H5OD reactants imply that the kinetically relevant step involves the cleavage of C-O bonds via a carbenium-ion transition state.
- 29Xin, H.; Li, X.; Fang, Y.; Yi, X.; Hu, W.; Chu, Y.; Zhang, F.; Zheng, A.; Zhang, H.; Li, X. Catalytic Dehydration of Ethanol over Post-Treated ZSM-5 Zeolites. J. Catal. 2014, 312, 204– 215, DOI: 10.1016/j.jcat.2014.02.003[Crossref], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlt1SrtLY%253D&md5=f8fcfe4949aa2e991f642035fa72034eCatalytic dehydration of ethanol over post-treated ZSM-5 zeolitesXin, Hongchuan; Li, Xiangping; Fang, Yuan; Yi, Xianfeng; Hu, Wenhui; Chu, Yueying; Zhang, Feng; Zheng, Anmin; Zhang, Hongpeng; Li, XuebingJournal of Catalysis (2014), 312 (), 204-215CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)Microporous ZSM-5 zeolite was post-treated by desilication with sodium hydroxide, dealumination with oxalic acid, or both of them in a sequential way to finely tune the zeolite catalysts with hierarchically porous structure and varying acidity. In the catalytic dehydration of ethanol, di-Et ether and ethylene were two main products competitively formed at 200 °C and atm. pressure. The post-treated ZSM-5 catalysts could display stable ethanol conversion and ethylene selectivity within time-onstream of around 12 h. The correlation between the steady-state ethylene selectivity and the amt. of weak acid sites from ammonia temp.-programmed desorption (NH3-TPD) indicated that the weak acid sites facilitated the ethylene prodn. during ethanol transformation under present reaction conditions. The reaction pathways for di-Et ether and ethylene formations from ethanol were investigated by theor. calcn. Both the activation energies and natural charges of the transition states strongly supported that the selectivity for the di-Et ether tended to deteriorate with decreasing catalytic Bronsted acidity.
- 30Kadam, S. A.; Shamzhy, M. V. IR Operando Study of Ethanol Dehydration over MFI Zeolites. Catal. Today 2018, 304, 51– 57, DOI: 10.1016/j.cattod.2017.09.020[Crossref], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFCltLvO&md5=aef41258862c91d5a8579f5b95d7ad96IR Operando study of ethanol dehydration over MFI zeoliteKadam, Shashikant A.; Shamzhy, Mariya V.Catalysis Today (2018), 304 (), 51-57CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Zeolite-catalyzed dehydration of ethanol is an attractive economically feasible route for prodn. of ethylene and butenes. The goal of this contribution is to monitor the intermediate species on the surface of "working" catalyst to rationalize the influence of the reaction conditions and zeolite characteristics on the dehydration pathways. With this respect the rates of di-Et ether (DEE) and ethylene formation in ethanol dehydration along with the quantification of the surface-intermediates (ethanol monomer and dimer) were simultaneously assessed under different reaction conditions in H-MFI zeolite. The reaction conditions (pressure, temp., and ethanol conversion) control the population of surface intermediates and hence det. the dominant reaction mechanism. The results support the prevalence of dimer-assisted etherification at high ethanol pressures and enhanced contribution of ethoxide-mediated route with increasing the temp. At high conversion, the DEE decompn. route producing ethylene was confirmed for H-MFI at 488 K along with ethoxide-mediated pathway.
- 31Zhang, M.; Yu, Y. Dehydration of Ethanol to Ethylene. Ind. Eng. Chem. Res. 2013, 52, 9505– 9514, DOI: 10.1021/ie401157c[ACS Full Text], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXps1yhs7o%253D&md5=83268b814a7d0f7b41c6fc3c948aec74Dehydration of Ethanol to EthyleneZhang, Minhua; Yu, YingzheIndustrial & Engineering Chemistry Research (2013), 52 (28), 9505-9514CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)A review. This article is an up-to-date review of the literature available on the subject of ethanol to ethylene. The process of ethanol to ethylene has broad development prospects. Compared with the process of petroleum to ethylene, ethanol dehydration to ethylene is economically feasible. Researchers have been redirecting their interest to the ethylene prodn. process, catalysts, and reaction mechanisms. A fluidized bed reactor, together with a wear-resistant, efficient, and stable catalyst will be the focus of future research that includes a deep understanding of the large-scale activated alumina catalyst and the mol. sieve catalyst used, and will promote the development of the ethanol dehydration to ethylene process and provide strong support for the market competiveness of the process.
- 32Sun, J.; Wang, Y. Recent Advances in Catalytic Conversion of Ethanol to Chemicals. ACS Catal. 2014, 4, 1078– 1090, DOI: 10.1021/cs4011343[ACS Full Text], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXisVWhtb4%253D&md5=48b977998a0baaf0eb01a6419041f892Recent Advances in Catalytic Conversion of Ethanol to ChemicalsSun, Junming; Wang, YongACS Catalysis (2014), 4 (4), 1078-1090CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review. With increased availability and decreased cost, ethanol is potentially a promising platform mol. for the prodn. of a variety of value-added chems. In this review, we provide a detailed summary of recent advances in catalytic conversion of ethanol to a wide range of chems. and fuels. We particularly focus on catalyst advances and fundamental understanding of reaction mechanisms involved in ethanol steam reforming (ESR) to produce hydrogen, ethanol conversion to hydrocarbons ranging from light olefins to longer chain alkenes/alkanes and aroms., and ethanol conversion to other oxygenates including 1-butanol, acetaldehyde, acetone, di-Et ether, and Et acetate.
- 33Varvarin, A. M.; Khomenko, K. M.; Brei, V. V. Conversion of N-Butanol to Hydrocarbons over H-ZSM-5, H-ZSM-11, H-L and H-Y Zeolites. Fuel 2013, 106, 617– 620, DOI: 10.1016/j.fuel.2012.10.032[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhslajs7nL&md5=7cc34ce36cab53b7bd5a7e2b4a27363bConversion of n-butanol to hydrocarbons over H-ZSM-5, H-ZSM-11, H-L and H-Y zeolitesVarvarin, Anatoliy M.; Khomenko, Kostyantyn M.; Brei, Volodymyr V.Fuel (2013), 106 (), 617-620CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)N-Butanol conversion to hydrocarbons over H-ZSM-5, H-ZSM-11, H-L and H-Y zeolites at 300-400 °C using a fixed bed flow reactor has been studied. All studied H-zeolites provide 100% alc. conversion at 300 °C. The conversion products are liq. (C5-10) hydrocarbons, gaseous (C<5) hydrocarbons, and water. Their wt. ratios are equal to 1:0.4:0.4 for H-ZSM-5 and 1:0.6:0.5 for H-Y (at 350 °C). The yield of liq. hydrocarbons over the H-pentasils is higher (52-55 wt.%) than over large pore H-L and H-Y (43-48 wt.%). The liq. fraction obtained over H-ZSM-5 includes aroms. mainly whereas on H-Y the main product was olefins. It was shown that H-ZSM-5 (Si/Al = 20) is capable to provide the yield of liq. hydrocarbons on the level of 50-55 wt.% from spent alc. at load on a catalyst up to 20 mmol C4H9OH g-1cath-1.
- 34Kondo, J. N.; Yamazaki, H.; Osuga, R.; Yokoi, T.; Tatsumi, T. Mechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5. J. Phys. Chem. Lett. 2015, 6, 2243– 2246, DOI: 10.1021/acs.jpclett.5b00846[ACS Full Text], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXpsFKqu7k%253D&md5=46e91518ec91f8abdc7412ec91b209bcMechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5Kondo, Junko N.; Yamazaki, Hiroshi; Osuga, Ryota; Yokoi, Toshiyuki; Tatsumi, TakashiJournal of Physical Chemistry Letters (2015), 6 (12), 2243-2246CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The reaction mechanism of the decompn. of ethoxy species to ethene and acidic OH groups on H-ZSM-5 was studied by IR spectroscopy using isotope-labeled ethanol. The concerted mechanism occurring on both the ethoxy (acid) site and the counterpart lattice oxygen was suggested by GC-MS anal. of evolved d2-ethene and IR observation of the recovery of OH s groups on acid sites from the decompn. of CH3CD2O- ethoxy species. The concerted mechanism was further confirmed by the estn. of activation energy for decompn. of CH3CH2O-, CH3CD2O-, and CD3CD2O- ethoxy species, 122 ± 3, 125 ± 3, and 140 ± 5 kJ mol-1, resp., where the kinetic isotope effect was obsd. for the cleavage of the CH or CD bond of the Me group of the ethoxy species.
- 35Nishino, H.; Fujita, T.; Yamamoto, A.; Fujimori, T.; Fujino, A.; Ito, S.; Nakamura, J.; Hosono, H.; Kondo, T. Formation Mechanism of Boron-Based Nanosheet through the Reaction of MgB2 with Water. J. Phys. Chem. C 2017, 121, 10587– 10593, DOI: 10.1021/acs.jpcc.7b02348[ACS Full Text], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntVajt7g%253D&md5=7523116a9063f758043ec04fa878754eFormation Mechanism of Boron-Based Nanosheet through the Reaction of MgB2 with WaterNishino, Hiroaki; Fujita, Takeshi; Yamamoto, Akiyasu; Fujimori, Tomohiro; Fujino, Asahi; Ito, Shin-ichi; Nakamura, Junji; Hosono, Hideo; Kondo, TakahiroJournal of Physical Chemistry C (2017), 121 (19), 10587-10593CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)A recent expt. demonstrated that ultrasonication of MgB2 in water yields Mg-deficient hydroxyl-functionalized boron nanosheets at room temp. The authors examd. the mechanism of nanosheet formation. Anal. of the reaction products and temporal variation in pH and H2 prodn. shows that the reaction between MgB2 and water comprises two steps: (i) an ion-exchange process between protons and a part of Mg cations of MgB2 with its exfoliation and (ii) the hydrolysis reaction between Mg-deficient boron hydride and water to produce H2 and Mg-deficient hydroxyl-functionalized boron sheets. The sheets with a stacking periodicity of 0.70 nm were obtained as the supernatant of the reaction product of water with MgB2. The stacking sheets can be further exfoliated if the reaction is conducted under ultrasonication. The derived nanosheets are composed of sp2-bonded boron framework and possess a disordered structure contg. hydroxyl species and oxidized magnesium.
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Abstract
Figure 1
Figure 1. (a) Photograph of HB sheets in powder form and schematic of the proposed local structure.(13) (b) Conversion of ethanol vs temperature. The results for HB, B2O3, and MgB2 are plotted for various W/F (g·min/mmol) conditions (contact time, weight of the catalyst divided by the flow rate of C2H5OH).
Figure 2
Figure 2. (a) Conversion of ethanol on HB sheets as a function of reaction time at 573 K and W/F = 7.3 g·min/mmol, estimated from hydrocarbon production (blue circles) and ethanol consumption (red triangles). (b) Selectivity vs reaction time.
Figure 3
Figure 3. (a) Selectivity of ethanol reforming by HB as a function of temperature at W/F = 6.7 g·min/mmol. (b) Selectivity of ethanol reforming by HB at 573 K and W/F = 6.7, 13.6, and 27.2 g·min/mmol.
Figure 4
Figure 4. Arrhenius plot of the ethanol-reforming reaction rate (k) in the presence of HB sheets for W/F = 27.2, 13.6, and 6.7 g·min/mmol.
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- 1Wang, Y.; Mao, J.; Meng, X.; Yu, L.; Deng, D.; Bao, X. Catalysis with Two-Dimensional Materials Confining Single Atoms: Concept, Design, and Applications. Chem. Rev. 2019, 119, 1806– 1854, DOI: 10.1021/acs.chemrev.8b00501[ACS Full Text], [CAS], Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisFKgsr7M&md5=69cdbea511d7a75f74410dfc2a08d177Catalysis with Two-Dimensional Materials Confining Single Atoms: Concept, Design, and ApplicationsWang, Yong; Mao, Jun; Meng, Xianguang; Yu, Liang; Deng, Dehui; Bao, XinheChemical Reviews (Washington, DC, United States) (2019), 119 (3), 1806-1854CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Two-dimensional materials and single-atom catalysts are two frontier research fields in catalysis. A new category of catalysts with the integration of both aspects has been rapidly developed in recent years, and significant advantages were established to make it an independent research field. In this Review, we will focus on the concept of two-dimensional materials confining single atoms for catalysis. The new electronic states via the integration lead to their mutual benefits in activity, i.e., two-dimensional materials with unique geometric and electronic structures can modulate the catalytic performance of the confined single atoms, and in other cases the confined single atoms can in turn affect the intrinsic activity of two-dimensional materials. Three typical two-dimensional materials are mainly involved here, i.e., graphene, g-C3N4, and MoS2, and the confined single atoms include both metal and nonmetal atoms. First, we systematically introduce and discuss the classic synthesis methods, advanced characterization techniques, and various catalytic applications toward two-dimensional materials confining single-atom catalysts. Finally, the opportunities and challenges in this emerging field are featured on the basis of its current development.
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- 3Zhang, Z.; Penev, E. S.; Yakobson, B. I. Two-Dimensional Boron: Structures, Properties and Applications. Chem. Soc. Rev. 2017, 46, 6746– 6763, DOI: 10.1039/C7CS00261K[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslemt7fL&md5=a507b9c3cadee04c317db61a3daf50e1Two-dimensional boron: structures, properties and applicationsZhang, Zhuhua; Penev, Evgeni S.; Yakobson, Boris I.Chemical Society Reviews (2017), 46 (22), 6746-6763CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)Situated between metals and non-metals in the periodic table, boron is one of the most chem. versatile elements, forming at least sixteen bulk polymorphs composed of interlinked boron polyhedra. In low-dimensionality, boron chem. remains or becomes even more intriguing since boron clusters with several to tens of atoms favor planar or cage-like structures, which are similar to their carbon counterparts in terms of conformation and electronic structure. The similarity between boron and carbon has raised a question of whether there exists stable two-dimensional (2D) boron, as a conceptual precursor, from which other boron nanostructures may be built. Here, we review the current theor. and exptl. progress in realizing boron at. layers. Starting by describing a decade-long effort towards understanding the size-dependent structures of boron clusters, we present how theory plays a role in extrapolating boron clusters into 2D form, from a freestanding state to that on substrates, as well as in exploring practical routes for their synthesis that recently culminated in exptl. realization. While 2D boron has been revealed to have unusual mech., electronic and chem. properties, materializing its potential in practical applications remains largely impeded by lack of routes towards transfer from substrates and controlled synthesis of quality samples.
- 4Kondo, T. Recent Progress in Boron Nanomaterials. Sci. Technol. Adv. Mater. 2017, 18, 780– 804, DOI: 10.1080/14686996.2017.1379856[Crossref], [PubMed], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1M3is1egtg%253D%253D&md5=659efc3fbd09160230213cdb0d9397baRecent progress in boron nanomaterialsKondo Takahiro; Kondo Takahiro; Kondo TakahiroScience and technology of advanced materials (2017), 18 (1), 780-804 ISSN:1468-6996.Various types of zero, one, and two-dimensional boron nanomaterials such as nanoclusters, nanowires, nanotubes, nanobelts, nanoribbons, nanosheets, and monolayer crystalline sheets named borophene have been experimentally synthesized and identified in the last 20 years. Owing to their low dimensionality, boron nanomaterials have different bonding configurations from those of three-dimensional bulk boron crystals composed of icosahedra or icosahedral fragments. The resulting intriguing physical and chemical properties of boron nanomaterials are fascinating from the viewpoint of material science. Moreover, the wide variety of boron nanomaterials themselves could be the building blocks for combining with other existing nanomaterials, molecules, atoms, and/or ions to design and create materials with new functionalities and properties. Here, the progress of the boron nanomaterials is reviewed and perspectives and future directions are described.
- 5Jiao, Y.; Ma, F.; Bell, L.; Bilic, A.; Du, A. Two-Dimensional Boron Hydride Sheets:High Stability, Massless Dirac Fermions, and Excellent Mechanical Properties. Angew. Chem. Int. Ed. 2016, 55, 10292– 10295[Crossref], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1GjurjP&md5=2bc59a06dab5ee330422549b3e0decd6Two-Dimensional Boron Hydride Sheets: High Stability, Massless Dirac Fermions, and Excellent Mechanical PropertiesJiao, Yalong; Ma, Fengxian; Bell, John; Bilic, Ante; Du, AijunAngewandte Chemie, International Edition (2016), 55 (35), 10292-10295CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Two-dimensional (2D) boron sheets were successfully synthesized in recent expts., however, some important issues remain, including the dynamical instability, high energy, and the active surface of the sheets. To stabilize 2D boron layers, we have used d. functional theory and global min. search with the particle-swarm optimization method to predict four stable 2D boron hydride layers, namely the C2/m, Pbcm, Cmmm, and Pmmn sheets. The vibrational normal mode calcns. reveal all these structures are dynamically stable, indicating potential for successful exptl. synthesis. The calcd. Young's modulus indicates a high mech. strength for the C2/m and Pbcm phases. Most importantly, the C2/m, Pbcm, and Pmmn structures exhibit Dirac cones with massless Dirac fermions and the Fermi velocities for the Pbcm and Cmmm structures are even higher than that of graphene. The Cmmm phase is reported as the first discovery of Dirac ring material among boron-based 2D structures. The unique electronic structure of the 2D boron hydride sheets makes them ideal for nanoelectronics applications.
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- 7Mannix, A. J.; Kiraly, B.; Hersam, M. C.; Guisinger, N. P. Synthesis and Chemistry of Elemental 2D Materials. Nat. Rev. Chem. 2017, 1, 0014, DOI: 10.1038/s41570-016-0014[Crossref], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVOks7rM&md5=12a456493cf73178bc0fc01a35819009Synthesis and chemistry of elemental 2D materialsMannix, Andrew J.; Kiraly, Brian; Hersam, Mark C.; Guisinger, Nathan P.Nature Reviews Chemistry (2017), 1 (2), 0014CODEN: NRCAF7; ISSN:2397-3358. (Nature Research)A review. 2D materials have attracted considerable attention in the past decade for their superlative phys. properties. These materials consist of atomically thin sheets exhibiting covalent in-plane bonding and weak interlayer and layer-substrate bonding. Following the example of graphene, most emerging 2D materials are derived from structures that can be isolated from bulk phases of layered materials, which form a limited library for new materials discovery. Entirely synthetic 2D materials provide access to a greater range of properties through the choice of constituent elements and substrates. Of particular interest are elemental 2D materials, because they provide the most chem. tractable case for synthetic exploration. In this Review, we explore the progress made in the synthesis and chem. of synthetic elemental 2D materials, and offer perspectives and challenges for the future of this emerging field.
- 8Boustani, I. New Quasi-Planar Surfaces of Bare Boron. Surf. Sci. 1997, 370, 355– 363, DOI: 10.1016/S0039-6028(96)00969-7[Crossref], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXmsFCnsQ%253D%253D&md5=18c3da11837f6386092928972508ca6cNew quasi-planar surfaces of bare boronBoustani, IhsanSurface Science (1997), 370 (2-3), 355-363CODEN: SUSCAS; ISSN:0039-6028. (Elsevier)New very stable quasi-planar clusters of bare boron are found by systematic ab initio d. functional and quantum chem. methods. They are composed of dove-tailed hexagonal pyramids different from the classical forms of α- or β-rhombohedral boron crystallines. The quasi-planar structures are considered to be fragments of quasi-planar surfaces, which can easily be obtained and constructed from a basic unit of hexagonal pyramids. A new investigation on double layers of boron quasi-planar surfaces shows an increase in the stability of the system which can be related to the overlap of .vpi.-orbitals between the layers. Therefore, we predict the existence of a series of parallel boron layers, as in graphite. These proposed surfaces can serve as lightweight protective armor, as a neutron-absorber material in fission reactions, or as very high temp. semiconductors.
- 9Penev, E. S.; Bhowmick, S.; Sadrzadeh, A.; Yakobson, B. I. Polymorphism of Two-Dimensional Boron. Nano Lett. 2012, 12, 2441– 2445, DOI: 10.1021/nl3004754[ACS Full Text], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XlsVarsLY%253D&md5=2267c2e58b67aa9a8c5a6a198e0020c3Polymorphism of Two-Dimensional BoronPenev, Evgeni S.; Bhowmick, Somnath; Sadrzadeh, Arta; Yakobson, Boris I.Nano Letters (2012), 12 (5), 2441-2445CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The structural stability and diversity of elemental B layers are evaluated by treating them as pseudoalloy B1-x(vacancy)x, where x is a vacancy in the close-packed triangular B lattice. This approach allows for an elegant use of the cluster expansion method in combination with 1st-principles d.-functional theory calcns., leading to a thorough exploration of the configurational space. A finite range of compns. x is found where the ground-state energy is essentially independent of x, uncovering a variety of stable B-layer phases (all metallic) and suggesting polymorphism, in Stark contrast to graphene or hexagonal BN.
- 10Wu, X.; Dai, J.; Zhao, Y.; Zhuo, Z.; Yang, J.; Zeng, X. C. Two-Dimensional Boron Monolayer Sheets. ACS Nano 2012, 6, 7443– 7453, DOI: 10.1021/nn302696v[ACS Full Text], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtVKqurrK&md5=6428d25c89484b2b5a0da0ab56d7bbf0Two-Dimensional Boron Monolayer SheetsWu, Xiaojun; Dai, Jun; Zhao, Yu; Zhuo, Zhiwen; Yang, Jinlong; Zeng, Xiao ChengACS Nano (2012), 6 (8), 7443-7453CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Boron, a nearest-neighbor of carbon, is possibly the second element that can possess free-standing flat monolayer structures, evidenced by recent successful synthesis of single-walled and multiwalled boron nanotubes (MWBNTs). From an extensive structural search using the first-principles particle-swarm optimization (PSO) global algorithm, two boron monolayers (α1- and β1-sheet) are predicted to be the most stable α- and β-types of boron sheets, resp. Both boron sheets possess greater cohesive energies than the state-of-the-art two-dimensional boron structures (by more than 60 meV/atom based on d. functional theory calcn. using PBE0 hybrid functional), i.e., the α-sheet previously predicted by Tang and Ismail-Beigi and the g1/8- and g2/15-sheets (both belonging to the β-type) recently reported by Yakobson and co-workers. Moreover, the PBE0 calcn. predicts that the α-sheet is a semiconductor, while the α1-, β1-, g1/8-, and g2/15-sheets are all metals. When two α1 monolayers are stacked on top each other, the bilayer α1-sheet remains flat with an optimal interlayer distance of ∼3.62 Å, which is close to the measured interlayer distance (∼3.2 Å) in MWBNTs.
- 11Zhang, X.; Wu, T.; Wang, H.; Zhao, R.; Chen, H.; Wang, T.; Wei, P.; Luo, Y.; Zhang, Y.; Sun, X. Boron Nanosheet: An Elemental Two-Dimensional (2D) Material for Ambient Electrocatalytic N2 -to-NH3 Fixation in Neutral Media. ACS Catal. 2019, 9, 4609– 4615, DOI: 10.1021/acscatal.8b05134[ACS Full Text], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXnvFChtbk%253D&md5=7cfdf04f92fb1f02a920bc466a920589Boron Nanosheet: An Elemental Two-Dimensional (2D) Material for Ambient Electrocatalytic N2-to-NH3 Fixation in Neutral MediaZhang, Xiaoxue; Wu, Tongwei; Wang, Huanbo; Zhao, Runbo; Chen, Hongyu; Wang, Ting; Wei, Peipei; Luo, Yonglan; Zhang, Yanning; Sun, XupingACS Catalysis (2019), 9 (5), 4609-4615CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)The Haber-Bosch process for industrial NH3 prodn. suffers from harsh reaction conditions and serious CO2 emission. Electrochem. N2 redn. offers a C-neutral alternative for more energy-saving NH3 synthesis but requires active electrocatalysts for the N2 redn. reaction (NRR). In this Letter, B nanosheet (BNS) is proposed as an elemental two-dimensional (2D) material to effectively catalyze the NRR toward NH3 synthesis with excellent selectivity. When tested in 0.1M Na2SO4, such BNS catalyst attains a high faradaic efficiency of 4.04% and a large NH3 yield of 13.22 μg h-1 mgcat-1 at -0.80 V vs. reversible H electrode, with strong electrochem. durability. D. functional theory calcns. suggest that the B atoms of both oxidized and H-deactivated BNS can catalyze the NRR more effectively than clean BNS, and the rate-detg. step is the desorption process of the 2nd NH3 gas.
- 12Chen, Y.; Yu, G.; Chen, W.; Liu, Y.; Li, G.; Zhu, P.; Tao, Q.; Li, Q.; Liu, J.; Shen, X. Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2017, 139, 12370– 12373, DOI: 10.1021/jacs.7b06337[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFCju7bJ&md5=b3a29c5674c2b53c2522b2d4e8fd72a6Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution ReactionChen, Yanli; Yu, Guangtao; Chen, Wei; Liu, Yipu; Li, Guo-Dong; Zhu, Pinwen; Tao, Qiang; Li, Qiuju; Liu, Jingwei; Shen, Xiaopeng; Li, Hui; Huang, Xuri; Wang, Dejun; Asefa, Tewodros; Zou, XiaoxinJournal of the American Chemical Society (2017), 139 (36), 12370-12373CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Developing nonprecious hydrogen evolution electrocatalysts that can work well at large current densities (e.g., at 1000 mA/cm2: a value that is relevant for practical, large-scale applications) is of great importance for realizing a viable water-splitting technol. Herein we present a combined theor. and exptl. study that leads to the identification of α-phase molybdenum diboride (α-MoB2) comprising borophene subunits as a noble metal-free, superefficient electrocatalyst for the hydrogen evolution reaction (HER). Our theor. finding indicates, unlike the surfaces of Pt- and MoS2-based catalysts, those of α-MoB2 can maintain high catalytic activity for HER even at very high hydrogen coverage and attain a high d. of efficient catalytic active sites. Expts. confirm α-MoB2 can deliver large current densities in the order of 1000 mA/cm2, and also has excellent catalytic stability during HER. The theor. and exptl. results show α-MoB2's catalytic activity, esp. at large current densities, is due to its high cond., large d. of efficient catalytic active sites and good mass transport property.
- 13Nishino, H.; Fujita, T.; Cuong, N. T.; Tominaka, S.; Miyauchi, M.; Iimura, S.; Hirata, A.; Umezawa, N.; Okada, S.; Nishibori, E. Formation and Characterization of Hydrogen Boride Sheets Derived from MgB2 by Cation Exchange. J. Am. Chem. Soc. 2017, 139, 13761– 13769, DOI: 10.1021/jacs.7b06153[ACS Full Text], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFSrt7bJ&md5=8628d81604ddeeb0b6f5f403aacf1c73Formation and characterization of hydrogen boride sheets derived from MgB2 by cation exchangeNishino, Hiroaki; Fujita, Takeshi; Cuong, Nguyen Thanh; Tominaka, Satoshi; Miyauchi, Masahiro; Iimura, Soshi; Hirata, Akihiko; Umezawa, Naoto; Okada, Susumu; Nishibori, Eiji; Fujino, Asahi; Fujimori, Tomohiro; Ito, Shin-ichi; Nakamura, Junji; Hosono, Hideo; Kondo, TakahiroJournal of the American Chemical Society (2017), 139 (39), 13761-13769CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mech. properties as well as hydrogen storage capacity. Here, we report the exptl. realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an av. yield of 42.3% at room temp. The sheets feature an sp2-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray at. pair distribution functions, electron diffraction, transmission electron microscopy, photo absorption, core-level binding energy data, IR absorption, electron energy loss spectroscopy, and d. functional theory calcns. The established cation-exchange method for metal diboride opens new avenues for the mass prodn. of several types of boron-based 2D materials by countercation selection and functionalization.
- 14Tateishi, I.; Cuong, N. T.; Moura, C. A. S.; Cameau, M.; Ishibiki, R.; Fujino, A.; Okada, S.; Yamamoto, A.; Araki, M.; Ito, S. Semimetallicity of Free-Standing Hydrogenated Monolayer Boron from MgB2. Phys. Rev. Mater. 2019, 3, 024004 DOI: 10.1103/PhysRevMaterials.3.024004[Crossref], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFGrsrnP&md5=2e5513892fc90333cd10b9b9df7c3758Semimetallicity of free-standing hydrogenated monolayer boron from MgB2Tateishi, I.; Cuong, N. T.; Moura, C. A. S.; Cameau, M.; Ishibiki, R.; Fujino, A.; Okada, S.; Yamamoto, A.; Araki, M.; Ito, S.; Yamamoto, S.; Niibe, M.; Tokushima, T.; Weibel, D. E.; Kondo, T.; Ogata, M.; Matsuda, I.Physical Review Materials (2019), 3 (2), 024004CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)Electronic states of a free-standing hydrogenated monolayer boron (HB) sheet were studied via soft x-ray spectroscopies at the B K-shell absorption edge and first-principles calcns. The HB sheet is semimetallic with electron and hole pockets at the Y and Γ points, resp. The electron band results from the B-H-B bonds formed during synthesis from a MgB2 crystal, while the hole band is kept through the process and originates from a honeycomb lattice boron layer or borophene in MgB2. Our results suggest that the HB sheet is a promising two-dimensional material for realizing new boron-based or superconducting nanodevices.
- 15Chen, L.; Chen, X.; Duan, C.; Huang, Y.; Zhang, Q.; Xiao, B. Reversible Hydrogen Storage in Pristine and Li Decorated 2D Boron Hydride. Phys. Chem. Chem. Phys. 2018, 20, 30304– 30311, DOI: 10.1039/C8CP05846F[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitF2qurbP&md5=cd8235d7cc5418e2b82a6099ad3caceeReversible hydrogen storage in pristine and Li decorated 2D boron hydrideChen, Long; Chen, Xianfei; Duan, Chao; Huang, Yi; Zhang, Qian; Xiao, BeibeiPhysical Chemistry Chemical Physics (2018), 20 (48), 30304-30311CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Motived by the recent exptl. fabrication of two-dimensional boron hydride (BH) sheets (Nishino et al., J. Am. Chem. Soc. 2017, 139, 13761), we explore the feasibility of pristine and Li doped BH sheets as a hydrogen storage medium within the framework of d. functional theory. BH shows an unexpected high affinity to Li with a binding energy of -2.38 eV in comparison to other alkali and alk. earth metals (Na, K, Ca, Mg and Al), much larger than its bulk cohesive energy (-1.63 eV). Energy barriers of Li diffusion on BH are also detd. to be around 1.12 eV, showing both high dynamic and thermodn. stability without the issue of cluster formation. Moreover, Li decorated BH is expected to achieve a high theor. gravimetric d. of 11.57 wt% with an av. H2 adsorption energy of -0.17 eV, holding great potential in massive hydrogen storage. In addn. to the storage, thermodn. anal. on the desorption behaviors of H2 mols. is performed via N-P-T diagram, which demonstrates that most of the H2 mols. (8.30 wt%) could be released at 3 atm/100 °C. Thus, the Li-decorated BH sheets are expected to be applied as an efficient medium for hydrogen storage under ambient conditions.
- 16Abtew, T. A.; Shih, B. C.; Dev, P.; Crespi, V. H.; Zhang, P. Prediction of a Multicenter-Bonded Solid Boron Hydride for Hydrogen Storage. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 094108 DOI: 10.1103/PhysRevB.83.094108[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXkt1GjsLg%253D&md5=d31d98946049414237ef1475b2c921c0Prediction of a multicenter-bonded solid boron hydride for hydrogen storageAbtew, Tesfaye A.; Shih, Bi-ching; Dev, Pratibha; Crespi, Vincent H.; Zhang, PeihongPhysical Review B: Condensed Matter and Materials Physics (2011), 83 (9), 094108/1-094108/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)A layered solid boron hydride structure (B2H2) consisting of a hexagonal boron network and bridge hydrogen which has a gravimetric capacity of 8 wt.% hydrogen is predicted. The structural, electronic, and dynamical properties of the proposed structure are investigated using first-principles electronic structure methods. The absence of soft phonon modes confirms the dynamical stability of the proposed structure. Charging the structure significantly softens hydrogen related phonon modes. Boron modes, in contrast, are either hardened or not significantly affected by electron doping. Furthermore, self-doping the structure considerably reduces the energy barrier against hydrogen release. These results suggest that electrochem. charging or self-doping mechanisms may facilitate hydrogen release while the underlying boron network remains intact for subsequent rehydrogenation.
- 17Makaremi, M.; Mortazavi, B.; Singh, C. V. 2D Hydrogenated Graphene-like Borophene as a High Capacity Anode Material for Improved Li/Na Ion Batteries: A First Principles Study. Mater. Today Energy 2018, 8, 22– 28, DOI: 10.1016/j.mtener.2018.02.003
- 18Xiang, P.; Chen, X.; Xiao, B.; Wang, Z. M. Highly Flexible Hydrogen Boride Monolayers as Potassium-Ion Battery Anodes for Wearable Electronics. ACS Appl. Mater. Interfaces 2019, 11, 8115– 8125, DOI: 10.1021/acsami.8b22214[ACS Full Text], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlChu78%253D&md5=106434c435c2774e3bc34acf2eb30d80Highly Flexible Hydrogen Boride Monolayers as Potassium-Ion Battery Anodes for Wearable ElectronicsXiang, Pan; Chen, Xianfei; Xiao, Beibei; Wang, Zhiming M.ACS Applied Materials & Interfaces (2019), 11 (8), 8115-8125CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)The rapid development of wearable electronics revealed an urgent need of low-cost, high-flexible, and high-capacity power sources. In this sense, emerging rechargeable K-ion batteries (KIBs) are promising candidate owing to their abundant resources, low-cost and lower redox potential in nonaq. electrolytes compared to Li-ion batteries. However, the fabrication of flexible KIBs remains highly challenging because of the lack of high-performance flexible electrode materials. The authors studied the mech. properties and electrochem. performance of recently developed H boride (BH) monolayer as a high-performance anode material based on d. functional theory (DFT) formalism. (i) BH presents ultra-low out-of-plane bending stiffness, rivaling that of graphene, which endows it with better flexibility to accommodate the repeat bending, rolling and folding on wearable device operation; (ii) high in-plane stiffness (157 N/m along armchair and 109 N/m along zigzag) in BH makes the electrode stable against pulverization upon external and internal strains. More importantly, BH electrode delivers low voltage of ∼0.24 eV in addn. to desired K-ion affinity and hopping resistance which remains very stable with the bending curvature. Emerged H vacancies in electrode improve both the K-ion intercalation and K-ion hopping, yielding a high theor. capacity (1138 mAh/g), which was among the highest reported values in the literature for K-ion anode materials. All the presented results suggested that a BH electrode could be used as a brand-new flexible and lightwt. KIB anode with high capacity, low voltage, and desired rate performance.
- 19Shukla, V.; Araujo, R. B.; Jena, N. K.; Ahuja, R. Borophene’s Tryst with Stability: Exploring 2D Hydrogen Boride as an Electrode for Rechargeable Batteries. Phys. Chem. Chem. Phys. 2018, 20, 22008– 22016, DOI: 10.1039/C8CP03686A[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsVWqt7zK&md5=464f61c13302f3a98f43c043a5e49093Borophene's tryst with stability: exploring 2D hydrogen boride as an electrode for rechargeable batteriesShukla, Vivekanand; Araujo, Rafael B.; Jena, Naresh K.; Ahuja, RajeevPhysical Chemistry Chemical Physics (2018), 20 (34), 22008-22016CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Graphene's emergence can be viewed as a pos. upheaval in 2D materials research. Along the same line, the realization of a related elemental 2D material, borophene, is another breakthrough. To circumvent the stability issues of borophene, which is reported to have been synthesized on metallic substrates under extreme conditions, hydrogenation of borophene (otherwise called as borophane or hydrogen boride or boron hydride) has been a plausible soln., but only proposed computationally. A recent report brings to fore its exptl. realization. Our current study delves into the possibilities of employing this intriguing 2D hydrogen boride as anodes in Li/Na ion batteries. Using first-principles d. functional theory methods, we computed relevant properties such as the ion (Li/Na) adsorption behavior, the possible pathways of ionic diffusion with the estn. of barriers as well as the theor. specific capacities and av. voltages to uniquely demonstrate that this material is of particular significance for battery applications. It is noted that the use of hydrogen boride leads to a high specific capacity of 861.78 mA h g-1 for Li ions, which is remarkably higher than the value reported in relation to its computationally predicted structure. Furthermore, Na ion intercalation leads to neg. voltage profiles, implying the unsuitability of 2D hydrogen boride for this particular ion. Our findings are timely and pertinent towards adding insightful details relevant to the progress of applications of 2D materials for energy storage.
- 20Bakoyannakis, D. N.; Zamboulis, D.; Stalidis, G. A.; Deliyanni, E. A. The Effect of Preparation Method on the Catalytic Activity of Amorphous Aluminas in Ethanol Dehydration. J. Chem. Technol. Biotechnol. 2001, 76, 1159– 1164, DOI: 10.1002/jctb.487[Crossref], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXotVSgtbc%253D&md5=c677a1f23f035b840e698033c68c6790The effect of preparation method on the catalytic activity of amorphous aluminas in ethanol dehydrationBakoyannakis, Demetris N.; Zamboulis, Demetris; Stalidis, George A.; Deliyanni, Eleni A.Journal of Chemical Technology & Biotechnology (2001), 76 (11), 1159-1164CODEN: JCTBED; ISSN:0268-2575. (John Wiley & Sons Ltd.)The known heterogeneous catalytic dehydration of ethanol on amorphous aluminum oxide samples was adopted as a measure of catalytic activity and selectivity. The aluminum oxide samples were prepd. by hydrolysis of aluminum chloride using propylamine, as proton acceptor, in pure and mixed aq. ethanolic and acetonic media, freeze dried and activated. The catalytic activity and selectivity of the samples was measured in the temp. range 623-698 K for various flow rates of ethanol. The apparent activation energies were calcd. (53-78 kJ mol-1) and depended on the solvent used in the prepn. of the aluminas. The effect of solvent medium on the activity and selectivity was discussed.
- 21Christiansen, M. A.; Mpourmpakis, G.; Vlachos, D. G. Density Functional Theory-Computed Mechanisms of Ethylene and Diethyl Ether Formation from Ethanol on γ-Al2O3(100). ACS Catal. 2013, 3, 1965– 1975, DOI: 10.1021/cs4002833[ACS Full Text], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtF2ru7nM&md5=377f38379dc750e27d3ecfc736b804b1Density Functional Theory-Computed Mechanisms of Ethylene and Diethyl Ether Formation from Ethanol on γ-Al2O3(100)Christiansen, Matthew A.; Mpourmpakis, Giannis; Vlachos, Dionisios G.ACS Catalysis (2013), 3 (9), 1965-1975CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Multiple potential active sites on the surface of γ-Al2O3 have led to debate about the role of Lewis and/or Bronsted acidity in reactions of ethanol, while mechanistic insights into competitive prodn. of ethylene and di-Et ether are scarce. In this study, elementary adsorption and reaction mechanisms for ethanol dehydration and etherification are studied on the γ-Al2O3(100) surface using d. functional theory calcns. The O atom of adsorbed ethanol interacts strongly with surface Al (Lewis acid) sites, while adsorption is weak on Bronsted (surface H) and surface O sites. Water, a byproduct of both ethylene and di-Et ether formation, competes with ethanol for adsorption sites. Multiple pathways for ethylene formation from ethanol are explored, and a concerted Lewis-catalyzed elimination (E2) mechanism is found to be the energetically preferred pathway, with a barrier of Ea = 37 kcal/mol at the most stable site. Di-Et ether formation mechanisms presented for the first time on γ-Al2O3 indicate that the most favorable pathways involve Lewis-catalyzed SN2 reactions (Ea = 35 kcal/mol). Addnl. novel mechanisms for di-Et ether decompn. to ethylene are reported. Bronsted-catalyzed mechanisms for ethylene and ether formation are not favorable on the (100) facet because of weak adsorption on Bronsted sites. These results explain multiple exptl. observations, including the competition between ethylene and di-Et ether formation on alumina surfaces.
- 22Pan, Q.; Ramanathan, A.; Kirk Snavely, W.; Chaudhari, R. V.; Subramaniam, B. Intrinsic Kinetics of Ethanol Dehydration over Lewis Acidic Ordered Mesoporous Silicate, Zr-KIT-6. Top. Catal. 2014, 57, 1407– 1411, DOI: 10.1007/s11244-014-0311-7[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVyrtr3M&md5=6e65781e3e82c8c3aae5c770d4512804Intrinsic Kinetics of Ethanol Dehydration Over Lewis Acidic Ordered Mesoporous Silicate, Zr-KIT-6Pan, Qing; Ramanathan, Anand; Kirk Snavely, W.; Chaudhari, Raghunath V.; Subramaniam, BalaTopics in Catalysis (2014), 57 (17-20), 1407-1411CODEN: TOCAFI; ISSN:1022-5528. (Springer)Lewis acidic Zr-KIT-6 catalyst was tested for ethanol dehydration. Under the reaction conditions studied (T = 300-380 °C, P = 1 atm, Pethanol = 5 % in N2), Zr-KIT-6 materials showed high ethylene selectivity (∼80 %) with stable activity (60 h). The activation energy for ethanol dehydration to ethylene, estd. from intrinsic rate consts. normalized with respect to the Lewis acid sites, was approx. 79 ± 1 kJ/mol.
- 23Roca, F.; De Mourgues, L.; Trambouze, Y. Catalytic Dehydration of Ethanol over Silica-Alumina. J. Catal. 1969, 14, 107– 113, DOI: 10.1016/0021-9517(69)90414-X
- 24Maihom, T.; Khongpracha, P.; Sirijaraensre, J.; Limtrakul, J. Mechanistic Studies on the Transformation of Ethanol into Ethene over Fe-ZSM-5 Zeolite. ChemPhysChem 2013, 14, 101– 107, DOI: 10.1002/cphc.201200786[Crossref], [PubMed], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslSmu7rF&md5=7572347b1aff7dd9f1d8ea3ca07bfa03Mechanistic Studies on the Transformation of Ethanol into Ethene over Fe-ZSM-5 ZeoliteMaihom, Thana; Khongpracha, Pipat; Sirijaraensre, Jakkapan; Limtrakul, JumrasChemPhysChem (2013), 14 (1), 101-107CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)Ethanol, through the utilization of bioethanol as a chem. resource, has received considerable industrial attention as it provides an alternative route to produce more valuable hydrocarbons. Using a d. functional theory approach incorporating the M06-L functional, which includes dispersion interactions, a large 34T nanocluster model of Fe-ZSM-5 zeolite in which T is a Si or Al atom is employed to examine both the stepwise and concerted mechanisms of the transformation of ethanol into ethene. For the stepwise mechanism, ethanol dehydration commences from the first hydrogen abstraction of the ethanol OH group to form the ethoxide-hydroxide intermediate with a low activation energy of 17.7 kcal mol-1. Consequently, the ethoxide-hydroxide intermediate is decompd. into ethene through hydrogen abstraction from the ethoxide Me carbon to either the OH group of hydroxide or the oxygen of the ethoxide group with high activation energies of 64.8 and 63.5 kcal mol-1, resp. For the concerted mechanism, ethanol transformation into the ethene product occurs in a single step without intermediate formation, with an activation energy of 32.9 kcal mol-1.
- 25Chen, G.; Li, S.; Jiao, F.; Yuan, Q. Catalytic Dehydration of Bioethanol to Ethylene over TiO2/γ-Al2O3 Catalysts in Microchannel Reactors. Catal. Today 2007, 125, 111– 119, DOI: 10.1016/j.cattod.2007.01.071[Crossref], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXntF2lu74%253D&md5=31270fbfc97e7b279f0169918ede04a3Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactorsChen, Guangwen; Li, Shulian; Jiao, Fengjun; Yuan, QuanCatalysis Today (2007), 125 (1-2), 111-119CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Ethylene prodn. via catalytic dehydration of ethanol over TiO2/γ-Al2O3 catalysts in multi-microchannel reactors is reported. The physicochem. properties of these catalysts are characterized by X-ray diffraction and FT-IR spectra. The effects of operation parameters, such as ethanol concn., reaction temp., and liq. hourly space velocity, have been investigated exptl. The reaction results indicate that the catalysts doped with TiO2 have high ethanol conversion of 99.96% and ethylene selectivity of 99.4%. An ethylene yield of 26 g/(gcat h) can be achieved, which provides a very favorable foundation for intensification and miniaturization of the ethylene prodn. process using bioethanol.
- 26Takahara, I.; Saito, M.; Inaba, M.; Murata, K. Dehydration of Ethanol into Ethylene over Solid Acid Catalysts. Catal. Lett. 2005, 105, 249– 252, DOI: 10.1007/s10562-005-8698-1[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1aiur7K&md5=6caff1aa6565ea48a550394573f48e0eDehydration of Ethanol into Ethylene over Solid Acid CatalystsTakahara, Isao; Saito, Masahiro; Inaba, Megumu; Murata, KazuhisaCatalysis Letters (2005), 105 (3-4), 249-252CODEN: CALEER; ISSN:1011-372X. (Springer)The dehydration of ethanol into ethylene was investigated over various solid acid catalysts, such as zeolites and silica-alumina, at temps. ranging 453-573 K under atm. pressure. Ethylene was produced via di-Et ether during the dehydration process. H-mordenites were the most active for the dehydration. The catalyst activity could be correlated with the no. of strong Bronsted acid sites in the catalyst. Further, the H-mordenite was more stable with a SiO2/Al2O3 ratio of 90 than with a SiO2/Al2O3 ratio of 20.
- 27Madeira, F. F.; Gnep, N. S.; Magnoux, P.; Maury, S.; Cadran, N. Ethanol Transformation over HFAU, HBEA and HMFI Zeolites Presenting Similar Brønsted Acidity. Appl. Catal., A 2009, 367, 39– 46, DOI: 10.1016/j.apcata.2009.07.033[Crossref], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFGjtrzK&md5=7306851ba940b78754841845ca239383Ethanol transformation over HFAU, HBEA and HMFI zeolites presenting similar Bronsted acidityMadeira, F. Ferreira; Gnep, N. S.; Magnoux, P.; Maury, S.; Cadran, N.Applied Catalysis, A: General (2009), 367 (1-2), 39-46CODEN: ACAGE4; ISSN:0926-860X. (Elsevier B.V.)Ethanol transformation into higher hydrocarbons in one step by heterogeneous acid catalysis was studied, at 350° and 30 bar total pressure. Three zeolites (HFAU, HBEA and HZSM-5) were compared, which have the same quantity of Bronsted acid sites but different pore architecture. Large pore HFAU and HBEA zeolites gave mainly increasing yield of ethylene and di-Et ether with time-onstream, due to deactivation of the strongest acid sites, and only small amts. of C3+ hydrocarbons. This was explained by a faster deactivation of large pore zeolites due to fast coke formation which rapidly eliminates strong Bronsted acid sites, required for the transformation of ethylene into higher hydrocarbons. The coke mols. were identified as polyarom. compds. Medium pore zeolite HZSM-5 showed an important formation of C3+ hydrocarbons (mostly C5-C11 compds.) and small amts. of ethylene and di-Et ether. For this zeolite, after 16 h reaction, there was still complete ethanol transformation into C3+ hydrocarbons, despite a 55% loss of microporosity and 94% loss of Bronsted acidity. On HZSM-5, the deactivation is slower and the formation of C3+ hydrocarbons was obsd. even when the catalyst was satd. with coke mols. (high activity for the hydrogen transfer reactions). It could be possible that for this zeolite, the reaction occurs at the edge of the pore channel.
- 28Chiang, H.; Bhan, A. Catalytic Consequences of Hydroxyl Group Location on the Rate and Mechanism of Parallel Dehydration Reactions of Ethanol over Acidic Zeolites. J. Catal. 2010, 271, 251– 261, DOI: 10.1016/j.jcat.2010.01.021[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXltF2ju78%253D&md5=5f29462c9882b15b00b8c6c0af4ded71Catalytic consequences of hydroxyl group location on the rate and mechanism of parallel dehydration reactions of ethanol over acidic zeolitesChiang, Hsu; Bhan, AdityaJournal of Catalysis (2010), 271 (2), 251-261CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)The effects of zeolite topol. on the dehydration of oxygen-contg. mols. were probed in steady-state and isotopic chem. reactions of ethanol over proton-form zeolite materials (FER, MFI and MOR) at low temps. (368-409 K). The measured rate of di-Et ether (DEE) synthesis was largely independent of ethanol partial pressure on all proton-form zeolites (FER, MFI, and MOR), indicating that DEE formation involves the activation of ethanol dimers. The measured rate of DEE synthesis over H-FER increased with increasing ethylene pressure in expts. done with ethanol-ethylene mixts., reflecting the weaker adsorption of ethanol dimers on the FER framework compared to that on MFI and MOR materials, thereby resulting in the co-adsorption and reaction of ethylene with ethanol on FER materials. Ethylene prodn. was only obsd. on H-MOR because the small eight-membered ring side pockets protect ethanol monomers from forming bulky ethanol dimers. Secondary kinetic isotopic effects measured for ethylene synthesis rates using C2D5OD and C2H5OD reactants imply that the kinetically relevant step involves the cleavage of C-O bonds via a carbenium-ion transition state.
- 29Xin, H.; Li, X.; Fang, Y.; Yi, X.; Hu, W.; Chu, Y.; Zhang, F.; Zheng, A.; Zhang, H.; Li, X. Catalytic Dehydration of Ethanol over Post-Treated ZSM-5 Zeolites. J. Catal. 2014, 312, 204– 215, DOI: 10.1016/j.jcat.2014.02.003[Crossref], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlt1SrtLY%253D&md5=f8fcfe4949aa2e991f642035fa72034eCatalytic dehydration of ethanol over post-treated ZSM-5 zeolitesXin, Hongchuan; Li, Xiangping; Fang, Yuan; Yi, Xianfeng; Hu, Wenhui; Chu, Yueying; Zhang, Feng; Zheng, Anmin; Zhang, Hongpeng; Li, XuebingJournal of Catalysis (2014), 312 (), 204-215CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)Microporous ZSM-5 zeolite was post-treated by desilication with sodium hydroxide, dealumination with oxalic acid, or both of them in a sequential way to finely tune the zeolite catalysts with hierarchically porous structure and varying acidity. In the catalytic dehydration of ethanol, di-Et ether and ethylene were two main products competitively formed at 200 °C and atm. pressure. The post-treated ZSM-5 catalysts could display stable ethanol conversion and ethylene selectivity within time-onstream of around 12 h. The correlation between the steady-state ethylene selectivity and the amt. of weak acid sites from ammonia temp.-programmed desorption (NH3-TPD) indicated that the weak acid sites facilitated the ethylene prodn. during ethanol transformation under present reaction conditions. The reaction pathways for di-Et ether and ethylene formations from ethanol were investigated by theor. calcn. Both the activation energies and natural charges of the transition states strongly supported that the selectivity for the di-Et ether tended to deteriorate with decreasing catalytic Bronsted acidity.
- 30Kadam, S. A.; Shamzhy, M. V. IR Operando Study of Ethanol Dehydration over MFI Zeolites. Catal. Today 2018, 304, 51– 57, DOI: 10.1016/j.cattod.2017.09.020[Crossref], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFCltLvO&md5=aef41258862c91d5a8579f5b95d7ad96IR Operando study of ethanol dehydration over MFI zeoliteKadam, Shashikant A.; Shamzhy, Mariya V.Catalysis Today (2018), 304 (), 51-57CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Zeolite-catalyzed dehydration of ethanol is an attractive economically feasible route for prodn. of ethylene and butenes. The goal of this contribution is to monitor the intermediate species on the surface of "working" catalyst to rationalize the influence of the reaction conditions and zeolite characteristics on the dehydration pathways. With this respect the rates of di-Et ether (DEE) and ethylene formation in ethanol dehydration along with the quantification of the surface-intermediates (ethanol monomer and dimer) were simultaneously assessed under different reaction conditions in H-MFI zeolite. The reaction conditions (pressure, temp., and ethanol conversion) control the population of surface intermediates and hence det. the dominant reaction mechanism. The results support the prevalence of dimer-assisted etherification at high ethanol pressures and enhanced contribution of ethoxide-mediated route with increasing the temp. At high conversion, the DEE decompn. route producing ethylene was confirmed for H-MFI at 488 K along with ethoxide-mediated pathway.
- 31Zhang, M.; Yu, Y. Dehydration of Ethanol to Ethylene. Ind. Eng. Chem. Res. 2013, 52, 9505– 9514, DOI: 10.1021/ie401157c[ACS Full Text], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXps1yhs7o%253D&md5=83268b814a7d0f7b41c6fc3c948aec74Dehydration of Ethanol to EthyleneZhang, Minhua; Yu, YingzheIndustrial & Engineering Chemistry Research (2013), 52 (28), 9505-9514CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)A review. This article is an up-to-date review of the literature available on the subject of ethanol to ethylene. The process of ethanol to ethylene has broad development prospects. Compared with the process of petroleum to ethylene, ethanol dehydration to ethylene is economically feasible. Researchers have been redirecting their interest to the ethylene prodn. process, catalysts, and reaction mechanisms. A fluidized bed reactor, together with a wear-resistant, efficient, and stable catalyst will be the focus of future research that includes a deep understanding of the large-scale activated alumina catalyst and the mol. sieve catalyst used, and will promote the development of the ethanol dehydration to ethylene process and provide strong support for the market competiveness of the process.
- 32Sun, J.; Wang, Y. Recent Advances in Catalytic Conversion of Ethanol to Chemicals. ACS Catal. 2014, 4, 1078– 1090, DOI: 10.1021/cs4011343[ACS Full Text], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXisVWhtb4%253D&md5=48b977998a0baaf0eb01a6419041f892Recent Advances in Catalytic Conversion of Ethanol to ChemicalsSun, Junming; Wang, YongACS Catalysis (2014), 4 (4), 1078-1090CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review. With increased availability and decreased cost, ethanol is potentially a promising platform mol. for the prodn. of a variety of value-added chems. In this review, we provide a detailed summary of recent advances in catalytic conversion of ethanol to a wide range of chems. and fuels. We particularly focus on catalyst advances and fundamental understanding of reaction mechanisms involved in ethanol steam reforming (ESR) to produce hydrogen, ethanol conversion to hydrocarbons ranging from light olefins to longer chain alkenes/alkanes and aroms., and ethanol conversion to other oxygenates including 1-butanol, acetaldehyde, acetone, di-Et ether, and Et acetate.
- 33Varvarin, A. M.; Khomenko, K. M.; Brei, V. V. Conversion of N-Butanol to Hydrocarbons over H-ZSM-5, H-ZSM-11, H-L and H-Y Zeolites. Fuel 2013, 106, 617– 620, DOI: 10.1016/j.fuel.2012.10.032[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhslajs7nL&md5=7cc34ce36cab53b7bd5a7e2b4a27363bConversion of n-butanol to hydrocarbons over H-ZSM-5, H-ZSM-11, H-L and H-Y zeolitesVarvarin, Anatoliy M.; Khomenko, Kostyantyn M.; Brei, Volodymyr V.Fuel (2013), 106 (), 617-620CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)N-Butanol conversion to hydrocarbons over H-ZSM-5, H-ZSM-11, H-L and H-Y zeolites at 300-400 °C using a fixed bed flow reactor has been studied. All studied H-zeolites provide 100% alc. conversion at 300 °C. The conversion products are liq. (C5-10) hydrocarbons, gaseous (C<5) hydrocarbons, and water. Their wt. ratios are equal to 1:0.4:0.4 for H-ZSM-5 and 1:0.6:0.5 for H-Y (at 350 °C). The yield of liq. hydrocarbons over the H-pentasils is higher (52-55 wt.%) than over large pore H-L and H-Y (43-48 wt.%). The liq. fraction obtained over H-ZSM-5 includes aroms. mainly whereas on H-Y the main product was olefins. It was shown that H-ZSM-5 (Si/Al = 20) is capable to provide the yield of liq. hydrocarbons on the level of 50-55 wt.% from spent alc. at load on a catalyst up to 20 mmol C4H9OH g-1cath-1.
- 34Kondo, J. N.; Yamazaki, H.; Osuga, R.; Yokoi, T.; Tatsumi, T. Mechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5. J. Phys. Chem. Lett. 2015, 6, 2243– 2246, DOI: 10.1021/acs.jpclett.5b00846[ACS Full Text], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXpsFKqu7k%253D&md5=46e91518ec91f8abdc7412ec91b209bcMechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5Kondo, Junko N.; Yamazaki, Hiroshi; Osuga, Ryota; Yokoi, Toshiyuki; Tatsumi, TakashiJournal of Physical Chemistry Letters (2015), 6 (12), 2243-2246CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The reaction mechanism of the decompn. of ethoxy species to ethene and acidic OH groups on H-ZSM-5 was studied by IR spectroscopy using isotope-labeled ethanol. The concerted mechanism occurring on both the ethoxy (acid) site and the counterpart lattice oxygen was suggested by GC-MS anal. of evolved d2-ethene and IR observation of the recovery of OH s groups on acid sites from the decompn. of CH3CD2O- ethoxy species. The concerted mechanism was further confirmed by the estn. of activation energy for decompn. of CH3CH2O-, CH3CD2O-, and CD3CD2O- ethoxy species, 122 ± 3, 125 ± 3, and 140 ± 5 kJ mol-1, resp., where the kinetic isotope effect was obsd. for the cleavage of the CH or CD bond of the Me group of the ethoxy species.
- 35Nishino, H.; Fujita, T.; Yamamoto, A.; Fujimori, T.; Fujino, A.; Ito, S.; Nakamura, J.; Hosono, H.; Kondo, T. Formation Mechanism of Boron-Based Nanosheet through the Reaction of MgB2 with Water. J. Phys. Chem. C 2017, 121, 10587– 10593, DOI: 10.1021/acs.jpcc.7b02348[ACS Full Text], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntVajt7g%253D&md5=7523116a9063f758043ec04fa878754eFormation Mechanism of Boron-Based Nanosheet through the Reaction of MgB2 with WaterNishino, Hiroaki; Fujita, Takeshi; Yamamoto, Akiyasu; Fujimori, Tomohiro; Fujino, Asahi; Ito, Shin-ichi; Nakamura, Junji; Hosono, Hideo; Kondo, TakahiroJournal of Physical Chemistry C (2017), 121 (19), 10587-10593CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)A recent expt. demonstrated that ultrasonication of MgB2 in water yields Mg-deficient hydroxyl-functionalized boron nanosheets at room temp. The authors examd. the mechanism of nanosheet formation. Anal. of the reaction products and temporal variation in pH and H2 prodn. shows that the reaction between MgB2 and water comprises two steps: (i) an ion-exchange process between protons and a part of Mg cations of MgB2 with its exfoliation and (ii) the hydrolysis reaction between Mg-deficient boron hydride and water to produce H2 and Mg-deficient hydroxyl-functionalized boron sheets. The sheets with a stacking periodicity of 0.70 nm were obtained as the supernatant of the reaction product of water with MgB2. The stacking sheets can be further exfoliated if the reaction is conducted under ultrasonication. The derived nanosheets are composed of sp2-bonded boron framework and possess a disordered structure contg. hydroxyl species and oxidized magnesium.
Supporting Information
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Origin of the induction period, TDS, effect of water, and catalytic activity of HB without pretreatment heating (PDF)
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