The indole scaffold will continue to play a vital part in the future of drug discovery and agrochemical development. Because of this, the necessity for elegant techniques to enable selective C–H functionalization is vast. Early developments have led to primarily C2 and C3 functionalization because of the inherent reactivity of the pyrrole ring. Despite this, elegant methods have been developed to enable selective C–H functionalization on the benzenoid moiety at C4, C5, C6, and C7. This review focuses on the contributions made in benzenoid C–H functionalization of indoles and other related heteroaromatics such as carbazoles.

The selective oxidation of propylene to acrolein is an important reaction in the chemical industry which has been extensively studied over the last few decades. Today, spectroscopic, computational, and synthetic approaches allow a renewed view of this established and well-understood catalytic process at a fundamental level. Consequently, a revised mechanistic pathway for the selective propylene oxidation over bismuth molybdates has been suggested recently. Furthermore, studies concerning the local interaction of specific surface entities as well as concepts from semiconductor science have provided valuable information to describe the operation mode of oxidation catalysts. New synthetic methods can be used not only to tune the specific surface area and surface species of a catalyst but also to give direct access to distinct metal oxide phases or specific crystalline phases with a synergetic interplay on the nanoscale. Since complex multicomponent systems, which exhibit both higher selectivity and activity in comparison to pure bismuth molybdates, are used for industrial applications, it is important to transfer the research concepts from such model systems to those more complex systems. This also involves operando characterization techniques on multiple length scales. Recent research activities shine a renewed light on this well-studied reaction, which therefore may become one of the drivers in selective oxidation catalysis to apply and further establish new tools that have been developed in theory, modeling, synthesis, and operando spectroscopy.

Catalytic oxidative functionalizations of simple, nonpolarized alkenes represent one of the lynchpin technologies in the realm of modern methodological chemical research. In this context, Lewis-acidic selenium species have experienced a steadily increasing scope of applications in catalytic oxidations of simple alkenes throughout recent years. In analogy to their metallic counterparts, such as cationic gold and platinum complexes, selenenium ions (i.e., RSe⁺) display an exceptional reactivity toward π-bonds, which allows for the highly chemoselective electrophilic functionalization of alkenes. This distinct reactivity profile enabled the development of a diverse array of catalytic bond-forming processes, such as allylic and vinylic aminations, inter- and intramolecular esterifications, halogenations, and etherifications. Remarkable features associated with such protocols are the high regiocontrol, the commonly mild reaction conditions, the operational simplicity by which selenium-catalyzed alkene oxidations can be conducted, and the exquisite functional group tolerance. These aspects make selenium-π-acid catalysis very attractive for late-stage oxidations of polyfunctionalized molecules, an asset that still remains to be fully explored. In this Perspective, the latest contributions to the field of selenium-π-acid catalysis are delineated and placed into context with indicatory insights gained from previous methodological, mechanistic, and theoretical studies.

Nanoporous metals with their distinct three-dimensional interconnected porous networks are promising materials as electrocatalysts for fundamental studies and practical applications because they have highly conductive self-supporting porous structures with large electrochemical surface areas. This Perspective provides an overview of the recent developments and state-of-the-art nanoporous metals as electrocatalysts for various important electrochemical systems. Potential strategies and opportunities for utilizing the unique characteristics of nanoporous metals to overcome typical problems faced in electrocatalysis are presented. Lastly, challenges regarding the synthesis of nanoporous metals with controlled porous structure and targeted surface catalytic sites are also discussed to stimulate new ideas and interests for nanoporous metallic electrocatalysts.

This Perspective discusses catalytic hydrogenation reactions of alkenes, alkynes, and other unsaturated C–C substrates in which the catalyst design involves cooperative strategies that enable bifunctional H₂ activation and delivery. These approaches complement the more traditional use of single-site precious metal systems for such hydrogenation reactions in homogeneous catalysis. Strategies included in this Perspective are cooperation between (a) a catalytic metal site and a basic ligand residue, (b) a catalytic metal site and an acidic ligand residue, (c) frustrated acid/base pairs, and (d) two cocatalytic metal sites. Unique reactivity and selectivity patterns with nonprecious elements that have emerged from successful implementation of these strategies in catalytic transformations are emphasized.

Functionalized biaryl-containing motifs are among the most valuable synthetic scaffolds in organic chemistry with wide ranging commercial applications in pharmaceuticals, functional materials, and agrochemicals. Recently, there has been tremendous progress in the development of methods for functional-group-tolerant, cost-effective, and atom-economic ruthenium-catalyzed C–H arylation, providing attractive catalytic alternatives to traditional C–H functionalization and cross-coupling approaches. New ruthenium-catalyzed C–H arylation reactions have resulted in the development of attractive and highly efficient synthetic approaches to functionalized biaryls unavailable by other methods. New mechanistic manifolds have emerged, thus opening prospects for the development of a broad range of novel reactions. Strategies for the use of ruthenium catalysis in complex synthesis, including industrial applications, have been reported, validating the synthetic potential of this mode of reactivity. The development of new catalysts, availability of ruthenium complexes in multiple oxidation states, and efficiency of various catalytic cycles allow for C–H arylation strategies that have been difficult to achieve by using other metals. Herein, we discuss the most recent advances in ruthenium-catalyzed C–H arylation, with a focus on both mechanistic aspects and synthetic utility.

Silyloxyarenes are demonstrated to be a versatile substrate class in a variety of nickel-catalyzed coupling processes. The C(sp²)–O bond of aryl silyl ethers is directly transformed into C–H or C–Si bonds using Ti(O-i-Pr)₄ or trialkylsilanes as reagents using nickel catalysts with N-heterocyclic carbene (NHC) ligands. Paired with the useful characteristics of silyl protecting groups, these methods enable protected hydroxyls to directly participate in high-value bond-forming steps rather than requiring deprotection-activation strategies that conventional approaches require. These processes of silyloxyarenes provide reactivity complementary to widely used phenol derivatives such as aryl pivalates, carbamates, and methyl ethers, thus enabling a powerful strategy for sequential chemoselective derivatization of complex substrates without protecting group and activating group manipulations.

An efficient asymmetric aerobic oxidation of tetrahydroisoquinolines with terminal alkynes was realized under mild reaction conditions using O₂ as the sole oxidant. A chiral N,N′-dioxide/zinc(II)/iron(II) bimetallic cooperative catalytic system proves to be efficient for the formation of various α-alkynyl substituted tetrahydroisoquinolines in good to excellent yields and enantioselectivities. A primary mechanistic study supports an enantioselective electrophilic addition of zinc acetylide to the iminium intermediates, formed through a molecular O₂-involved oxidative process.

Cobalt dialkyl complexes bearing α-diimine ligands proved to be active precatalysts for the nondirected, C(sp³)–H selective hydrogen isotope exchange (HIE) of alkylarenes using D₂ gas as the deuterium source. Alkylarenes with a variety of substitution patterns and heteroatom substituents on the arene ring were successfully labeled, enabling high levels of incorporation into primary, secondary, and tertiary benzylic C(sp³)–H bonds. In some cases, the HIE proceeded with high diastereoselectivity and application of the cobalt-catalyzed method to enantioenriched substrates with benzylic stereocenters provided enantioretentive hydrogen isotope exchange at tertiary carbons.

A strategy for the synthesis of semitelechelic polyethylene through the palladium diimine-catalyzed chain-transfer polymerization of ethylene using various silanes as chain-transfer agents is reported. Polymer molecular weight and end-group chemical structure can be tuned by varying the chain-transfer agent as well as its concentration. NMR spectroscopy confirms that the silicon of the chain-transfer agent is incorporated into the polymer. The stability of the catalyst toward polar monomer enables the chain-transfer polymerization of semitelechelic poly(ethylene-methyl acrylate) copolymers.

A Rh–Sn nanoparticle is achieved by combinatorial approaches for application as an active and stable electrocatalyst in the oxygen reduction reaction. Both metallic Rh and metallic Sn exhibit activities too low to be utilized for electrocatalytic reduction of oxygen. However, a clean and active Rh surface can be activated by incorporation of Sn into a Rh nanoparticle through the combined effects of lateral repulsion, bifunctional mechanism, and electronic modification. The corrosion-resistant property of Rh contributes to the construction of a stable catalyst that can be used under harsh fuel cell conditions. Based on both theoretical and experimental research, Rh–Sn nanoparticle designs with inexpensive materials can be a potential alternative catalyst in terms of the economic feasibility of commercialization and its facile and simple surfactant-free microwave-assisted synthesis.

An electrochemical cyclization reaction of easily available urea-tethered diynes has been developed for the synthesis of nitrogen-doped polycyclic aromatic hydrocarbons (PAHs). The employment of ferrocene as a mild and selective redox catalyst allows access to a variety of electron-rich PAHs including helicene-like structures without overoxidation. The electrosynthetic method involves an unprecedented amidyl radical cascade cyclization process to form three rings in a single operation.

The folding mode of substrate FPP in sesquiterpene cyclases/synthases is key to the chemo- and stereoselectivity of the ultimate sesquiterpene products. However, the precise substrate folding modes in most sesquiterpene cyclases are still elusive, and it is challenging for theoretical simulations due to the high flexibility of FPP. Herein, by DFT/MM MD simulations, we obtain the optimal folding mode of FPP in the 1,6-closure trichodiene synthase and illuminate the whole catalytic mechanism for the biosynthesis of trichodiene. Furthermore, a simple and practical rule is proposed to decipher the relationship between the diverse FPP folding modes and chemical selectivity toward 1,6- and 1,10-ring closure, which are common pathways in all sesquiterpene cyclases.

Development of a highly efficient and robust water oxidation catalyst (WOC) with reduced usage of noble metals is extremely crucial for water splitting and CO₂ reduction by photocatalysis or electrolysis. Herein, we synthesized subnanometric iridium dioxide clusters supported on multiwalled carbon nanotubes (MWCNTs) by a chemical vapor deposition method (nominated as IrO₂/CNT). Benefiting from a mild oxidation process in air at 303 K, the deposited iridium clusters can be controlled to have a narrow size distribution from several atoms to 2 nm, having an average size of ca. 1.1 nm. The subnanometric iridium-containing sample is demonstrated to be highly efficient and robust for water oxidation. The optimal turnover frequency (TOF) of chemical water oxidation on the as-obtained sample can reach 11.2 s^–1, and the overpotential of electrochemical water oxidation is 249, and 293 mV at 10 mA cm^–2 in 1.0 M KOH (pH: 13.6), and 0.5 M H₂SO₄ (pH: 0), respectively. On the basis of the structural characterizations and theory simulation, the extraordinary performances of the ultrasmall iridium dioxide are proposed to mainly originate from enhanced number of unsaturated surface Ir atoms and change of local coordination environment. Our work highlights the importance of subnanometric size of iridium dioxide in water oxidation.

Single metal atoms and metal clusters have attracted much attention because of their high dispersity, special electronic structures, and uniformity of active sites as heterogeneous catalysts, but it is still challenging to generate stable single atoms and clusters with high metal loadings. Supports play a crucial role in determining particle morphology and maintaining dispersion. Herein we synthesize an amorphous alumina with 29% coordinatively unsaturated pentacoordinate Al³⁺ (Al³⁺_penta) sites, which can anchor atomically dispersed Ru species with 1 wt % loading. Strong interactions between Ru and Al³⁺_penta centers were detected, resulting in distinct Ru geometric and electronic features. When used in benzene hydrogenation reaction, fairly high specific activity (TOF = 5180 h^–1) were obtained. The high catalytic performance is considered closely correlated with the high utilization of special Ru active sites.

Chiral, cationic NHC-iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes. The catalysts show high activity in the construction of pyrrolidines, which are accessed with excellent optical purity. Enantiomerically enriched piperidines and indolines are also produced, and various functional groups are tolerated with this LTM system. A reaction mechanism is proposed, and a major deactivation pathway of these catalysts is presented and discussed.

A protocol for the aminomethylation of aryl halides using α-silylamines via Ni/photoredox dual catalysis is described. The low oxidation potential of these silylated species enables facile single electron transfer (SET) oxidation of the amine followed by rapid desilylation. The resulting α-amino radicals can be directly funneled into a nickel-mediated cross-coupling cycle with aryl halides. The process accomplishes aminomethylation under remarkably mild conditions and tolerates numerous aryl- and heteroaryl halides with an array of functional groups.

We report on an efficient Ir-catalyzed decarbonylation of glycerol, which could be coupled to an ensuing Pd-catalyzed alkoxycarbonylation of styrenes. The formation of hydrogen could be avoided by employing 1,4-benzoquinone (BQ) as an external oxidant. A wide variety of styrenes underwent the esterification in good yields and high regioselectivity. Applying catalytic amounts of hexafluoroisopropanol provided access to alcohols other than methanol, which this transformation is often limited to. Finally, we demonstrate the suitability of this methodology for the preparation of three well-known nonsteroidal anti-inflammatory drugs (NSAIDs).

Carbonyl-stabilized phosphonium ylides exhibit great utility in modern organic synthesis, and they are known as an ambident nucleophile at the carbonyl oxygen atom and at the α-carbon atom. However, they have found limited use as catalysts. We focused on the inherent nucleophilicity of the oxygen atom to develop an ionic nucleophilic catalysis, and the phosphonium ylide-catalyzed primary alcohol selective acylation of mixed diols with acid anhydrides has been demonstrated. Mechanistic studies revealed the behavior of a catalyst, which would contribute to the field of ylide chemistry.

A chiral dirhodium(II) paddlewheel complex has been synthesized from biscarboxylate ligands derived from BINOL, and the resulting complex has been used in enantioselective carbene/alkyne cascade reactions. The ligand design was guided by requirements of α,α-dimethyl substituted carboxylates and bidentate ligands to ensure high levels of catalytic activity. Previously disclosed chiral complexes lack these features, resulting in low product yields. The design successfully replicated or exceeded the yields of the unusually effective achiral catalyst for the cascade reaction, Rh₂(esp)₂, which often shows unique reactivity. Promising enantioselectivity was observed for aldehyde-derived hydrazone substrates (29–96% ee), showing that the new scaffold has significant potential.

Pd(II)-catalyzed C–H functionalization of nondirected arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C–H olefination reaction of electron-rich and electron-poor arenes. This methodology is operationally simple, scalable, and can be used in late-stage functionalization of complex molecules. The broad applicability of this catalyst has been showcased in other transformations such as Pd(II)-catalyzed C–H acetoxylation and allylation reactions.

Mn(I)-PNP pincer catalyzed sequential one-pot homogeneous CO₂ hydrogenation to CH₃OH by molecular H₂ is demonstrated. The hydrogenation consists of two parts—N-formylation of an amine utilizing CO₂ and H₂, and subsequent formamide reduction to CH₃OH, regenerating the amine in the process. A reported air-stable and well-defined Mn-PNP pincer complex was found active for the catalysis of both steps. CH₃OH yields up to 84% and 71% (w.r.t amine) were obtained, when benzylamine and morpholine were used as amines, respectively; and a TON of up to 36 was observed. In our opinion, this study represents an important development in the nascent field of base-metal-catalyzed homogeneous CO₂ hydrogenation to CH₃OH.

Reaction rates, product distributions, and catalyst deactivation are reported for SAPO-34, MgO, MoO₃, and physical blends of these materials in fixed-bed reactors. Methanol is converted to small olefins (C2 and C3 primarily) over SAPO-34. A small fraction of the methanol oligomerizes further, forming coke that deactivates the catalyst. Methanol is dehydrogenated to CO and H₂ over MgO catalysts. Methanol is oxidized to CO₂ over MoO₃ catalysts. Physically blending SAPO-34 with MgO or MoO₃ reduces the reaction selectivity for the methanol to olefins (MTO) reaction. Physical mixing of SAPO-34 and MgO favorably extends the catalyst lifetimes by reducing the rate of coke formation on SAPO-34. This is explained by opening up parallel reaction pathways involving oxygenated reaction intermediates. In contrast, SAPO-34 deactivation is more rapid when SAPO-34 is physically blended with MoO₃. MgO by itself shows almost no catalytic activity for methanol. However, when MgO is sandwiched between layers of SAPO-34, the catalytic activity and production distribution from methanol is significantly altered to favor carbon oxides in comparison to SAPO-34 by itself. MgO is only catalytically active when it is sandwiched between layers of SAPO-34, demonstrating that reaction intermediates are transported from SAPO-34 to MgO and back again. Blends of MoO₃ and SAPO-34 showed that catalyst deactivation was more rapid in comparison to SAPO-34 alone; methanol was oxidized to formaldehyde over MoO₃, which was transported to SAPO-34, where the acidic SAPO-34 catalyst is assumed to polymerize the formaldehyde. The data indicate that acid-catalyzed reactions critical to MTO, oligomerization, and scission reactions occur on SAPO-34. MgO-catalyzed methanol dehydrogenation and MoO₃-catalyzed methanol oxidation. Physical blends of catalysts can open up new reaction pathways through coupling of different catalyst functionalities that may provide a simple and convenient method for tuning catalytic performance.

The cysteine protease enzyme legumain hydrolyzes peptide bonds with high specificity after asparagine and under more acidic conditions after aspartic acid [Baker, E. N. J. Mol. Biol. 1980, 141, 441−484; Baker, E. N.; J. Mol. Biol. 1977, 111, 207–210; Drenth, J.; Biochemistry 1976, 15, 3731–3738; Menard, R.; J. Cell. Biochem. 1994, 137; Polgar, L. Eur. J. Biochem. 1978, 88, 513–521; Storer, A. C.; Methods Enzymol. 1994, 244, 486–500. Remarkably, legumain additionally exhibits ligase activity that prevails at pH > 5.5. The atomic reaction mechanisms including their pH dependence are only partly understood. Here we present a density functional theory (DFT)-based quantum mechanics/molecular mechanics (QM/MM) study of the detailed reaction mechanism of both activities for human legumain in solution. Contrasting the situation in other papain-like proteases, our calculations reveal that the active site Cys189 must be present in the protonated state for a productive nucleophilic attack and simultaneous rupture of the scissile peptide bond, consistent with the experimental pH profile of legumain-catalyzed cleavages. The resulting thioester intermediate (INT1) is converted by water attack on the thioester into a second intermediate, a diol (INT2), which is released by proton abstraction by Cys189. Surprisingly, we found that ligation is not the exact reverse of the proteolysis but can proceed via two distinct routes. Whereas the transpeptidation route involves aminolysis of the thioester (INT1), at pH 6 a cysteine-independent, histidine-assisted ligation route was found. Given legumain’s important roles in immunity, cancer, and neurodegenerative diseases, our findings open up possibilities for targeted drug design in these fields.

Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2–4 nm Au nanoparticulate catalysts, supported on either TiO₂ or SiO₂, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports. At full conversion of butadiene, only 0.1% of the propene was converted for both supported catalysts, demonstrating their high selectivity. The TiO₂-supported catalysts showed a steady loss of activity, which was recovered by heating in air. We demonstrated that the deactivation was not caused by significant metal particle growth or strong metal–support interaction, but rather, it is related to the deposition of carbonaceous species under reaction conditions. In contrast, all the SiO₂-supported catalysts were highly stable, with very limited formation of carbonaceous deposits. It shows that SiO₂-supported catalysts, despite their 2–3 times lower initial activities, clearly outperform TiO₂-supported catalysts within a day of run time.

We describe a general theory for surface-catalyzed bimolecular reactions in responsive nanoreactors, catalytically active nanoparticles coated by a stimuli-responsive “gating” shell, whose permeability controls the activity of the process. We address two archetypal scenarios encountered in this system: the first, where two species diffusing from a bulk solution react at the catalyst’s surface, and the second, where only one of the reactants diffuses from the bulk while the other is produced at the nanoparticle surface, e.g., by light conversion. We find that in both scenarios the total catalytic rate has the same mathematical structure, once diffusion rates are properly redefined. Moreover, the diffusional fluxes of the different reactants are strongly coupled, providing a behavior richer than that arising in unimolecular reactions. We also show that, in stark contrast to bulk reactions, the identification of a limiting reactant is not simply determined by the relative bulk concentrations but is controlled by the nanoreactor shell permeability. Finally, we describe an application of our theory by analyzing experimental data on the reaction between hexacyanoferrate(III) and borohydride ions in responsive hydrogel-based core–shell nanoreactors.

A Cu-catalyzed protocol has been developed for the rapid construction of a wide spectrum of structurally interesting spiropyrroline skeletons. This method utilizes readily accessible ketoximes and alkenes as the starting materials and exhibits broad substrate scope and good functional group compatibility. Furthermore, the reaction can be applied for the late-stage modification of bioactive pregnenolone derivatives. The mechanistic investigation suggests that the reactions proceed through a radical process.

Transition metal catalyzed cross-coupling reactions occupy a privileged position in chemistry because of their ability to link myriad functional groups. The numerous variants of this class of reactions (e.g., Suzuki, Kumada, Negishi, etc.) differ in the transmetalation agent used to transfer “R” groups onto the catalyst. While understanding any single variant (e.g., Suzuki coupling) can be accomplished through direct analysis of the catalytic cycle, a comprehensive picture that illustrates the interrelationships between the different types of cross-coupling reactions remains absent. Here, using a tool built upon a three-dimensional volcano plot, we create a generalized thermodynamic picture of C–C cross-coupling reactions. This “cross-coupling” genome not only facilitates better understanding of catalytic behavior but also outlines strategies for developing new reaction protocols through the manipulation of easily computed descriptor variables.

Iron and cobalt catalysts are two major categories for commercial Fischer–Tropsch synthesis (FTS) catalysts. The two types of catalysts have distinct merits and shortcomings while they are largely supplementary to each other. However, until now, there has been a lack of an efficient way to properly combine those two catalysts into a synergistic one which possesses the benefits of both catalysts. Herein, the Fe₅C₂/Co heterostructured nanoparticles (NPs) were constructed by a secondary growth strategy, where the Fe/Co molar ratio can be tuned from 3.3 to 25. Based on the FTS reaction evaluation, we observed that only with 0.6 wt % Co (Fe/Co = 12) incorporated, the Fe₅C₂/Co catalyst exhibits an activity four times higher than that of pure Fe₅C₂ catalyst at low temperature. In this catalyst, Co was responsible for the CO dissociation while Fe₅C₂ was responsible for the chain growth at 220 °C. The synergistic effect of both sites may lead to enhanced performance in FTS reaction. This result provides a perspective for the construction of Fe–Co bimetallic FTS catalysts.

A high-power mediated electron transfer type formate (HCOO^–)/dioxygen (O₂) biofuel cell is reported herein. The cell utilizes a Ketjen Black modified waterproof carbon cloth as the electrode material. The bioanode comprises tungsten-containing formate dehydrogenase and a viologen-functionalized polymer, whereas the biocathode comprises bilirubin oxidase and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate). In addition, a gas diffusion type system was employed for the biocathode to realize a high-speed O₂ supply. These electrodes exhibited a large current density of 20 mA cm^–2 in the quiescent steady state for both HCOO^– oxidation and O₂ reduction. Finally, these electrodes were coupled to construct an HCOO^–/O₂ biofuel cell without a separator. The cell exhibited a maximum power density of 12 mW cm^–2 at a cell voltage of 0.78 V under quiescent conditions and an open-circuit voltage of 1.2 V. We show the great potential of HCOO^– for the fuel of biofuel cells.

The overall objective of this research is to convert the increasingly concerning CO₂ and renewable H₂ to highly demanded methanol (CH₃OH), which creates a win–win scenario for simultaneous climate change prevention and sustainable economic development. The key to the success of this targeted CO₂ utilization technology is the development of low-pressure methanol synthesis catalysts (Ni_aIn_bAl/SiO₂; a = 0–8.3, b = 0–9.1) by means of a phyllosilicate precursor, allowing for formation of well-dispersed metallic particles with an average diameter of 2.5–3.5 nm. The catalysts were characterized with various methods including ICP-OES, N₂ physisorption, XRD, SEM, TEM, TGA, H₂ TPR, DRIFTS, and XPS. The performances of the Ni_aIn_bAl/SiO₂ catalysts and conventional catalyst were compared under various evaluation temperatures at ambient pressure. It was found that catalysts with Ni/In ratios of 0.4–0.7 showed the highest activity. Ni_3.5In_5.3Al/SiO₂ (NIA-0.7) with 15% metal loading was the best among the tested Ni_aIn_bAl/SiO₂ catalysts with an activity of 0.33 mol h^–1 (mol catalyst metal)⁻¹ in comparison to the benchmark Cu/ZnO/Al₂O₃ (CZA) catalyst at 0.17. Several Ni_aIn_bAl/SiO₂ catalysts also showed similar CO₂ conversions in comparison to the CZA catalyst. Infrared studies using DRIFTS determined that CO₂ hydrogenation on Ni_aIn_bAl/SiO₂ catalysts proceeds through monodentate carbonate before further conversion to monodentate and bidentate formate. With a feed of CO/H₂ instead of CO₂/H₂ the primary hydrocarbon product changes from methanol to propane, accompanied by a lack of formate and monodentate carbonate IR signals.

Catalytic enantioselective conjugate additions with easily accessible alkenylboronic acid pinacol esters as nucleophiles promoted by chiral copper complexes of N-heterocyclic carbenes are presented. These processes constitute an unprecedented instance of conjugate additions of a variety of functionalized alkenyl groups and afford desired products that are otherwise difficult to access in up to 98% yield and 99.5:0.5 enantiomeric ratio. The origins of ligand-controlled enantioselectivity are elucidated with density functional theory (DFT) calculations.

During application, electrocatalysts are exposed to harsh electrochemical conditions, which can induce degradation. This work addresses the degradation of AuPd bimetallic catalysts used for the electrocatalytic production of hydrogen peroxide (H₂O₂) by the oxygen reduction reaction (ORR). Potential-dependent changes in the AuPd surface composition occur because the two metals have different dissolution onset potentials, resulting in catalyst dealloying. Using a scanning flow cell (SFC) with an inductively coupled plasma mass spectrometer (ICP-MS), simultaneous Pd and/or Au dissolution can be observed. Thereafter, three accelerated degradation protocols (ADPs), simulating different dissolution regimes, are employed to study the catalyst structure degradation on the nanoscale with identical location (IL) TEM. When only Pd or both Au and Pd dissolve, the composition changes rapidly and the surface becomes enriched with Au, as observed by cyclic voltammetry and elemental mapping. Such changes are mirrored by the evolution of electrocatalytic performances toward H₂O₂ production. Our experimental findings are finally summarized in a dissolution/structure/selectivity mechanism, providing a clear picture of the degradation of bimetallic catalyst used for H₂O₂ synthesis.

The layered compounds and especially transition-metal dichalcogenides are at the forefront of current research on electrocatalytic materials. Despite the fact that electrocatalytical properties of molybdenum and tungsten disulfides are well-known, their tellurium analogues are significantly less explored. Here we show an effective method for MoTe₂ and WTe₂ chemical exfoliation based on alkali metal intercalation and subsequent reaction with water. The as-synthesized and exfoliated tellurides were characterized in detail and investigated for potential application in electrocatalysis. The inherent electrochemical activity related to both cation and anion was observed. This is dominantly related to the oxidation tendency of tellurium. The MoTe₂ and WTe₂ show significantly contrasting properties toward the hydrogen evolution reaction, where MoTe₂ shows highly increased HER activity with little dependence on electrochemical treatment, whereas WTe₂ shows slightly worse improvement and strong dependence on the electrochemical treatment. In particular, the exfoliated MoTe₂ exhibits improved electrocatalytic activity for hydrogen evolution reaction and possesses a huge application potential.

Rhodium (Rh) catalysts are among the major candidates for syngas conversion to higher oxygenates (C₂₊oxy), with manganese (Mn) as a commonly used promoter for enhancing the activity and selectivity toward C₂₊oxy. In this study, we use atomic layer deposition (ALD) to controllably modify Rh catalysts with MnO, by depositing manganese oxide as a support layer or an overlayer, in order to identify the function of the Mn promoter. We also compare the ALD-modified catalysts with those prepared by coimpregnation. An ultrathin MnO support layer shows the most effective enhancement for C₂₊oxy production. Transmission electron microscopy, temperature-programmed reduction, and diffuse reflectance infrared Fourier transform spectroscopy characterization indicates that formation of Rh–MnO interface sites is responsible for the observed activity and selectivity improvements, while ruling out Rh nanoparticle size and alloy or mixed oxide formation as significant contributors. MnO overlayers on Rh appear to suffer from poor stability upon CO adsorption and are less effective than a MnO support layer. Density functional theory (DFT) calculations show that MnO species on the Rh(111) surface lower the transition state energy for CO bond dissociation and stabilize the key transition state for C₂₊oxy synthesis more significantly than that for methane synthesis, leading to enhanced activity and C₂₊oxy selectivity.

Selectively cleaving the C═O bond of the aldehyde group in furfural is critical for converting this biomass-derived platform chemical to an important biofuel molecule, 2-methylfuran. This work combined density functional theory (DFT) calculations and temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) measurements to investigate the hydrodeoxygenation (HDO) activity of furfural on bimetallic surfaces prepared by modifying Pt(111) with 3d transition metals (Cu, Ni, Fe, and Co). The stronger binding energy of furfural and higher tilted degree of the furan ring on the Co-terminated bimetallic surface resulted in a higher activity for furfural HDO to produce 2-methylfuran in comparison to that on either Pt(111) or Pt-terminated PtCoPt(111). The 3d-terminated bimetallic surfaces with strongly oxophilic 3d metals (Co and Fe) showed higher 2-methylfuran yield in comparison to those surfaces modified with weakly oxophilic 3d metals (Cu and Ni). The effect of oxygen on the HDO selectivity was also investigated on oxygen-modified bimetallic surfaces, revealing that the presence of surface oxygen resulted in a decrease in 2-methylfuran yield. The combined theoretical and experimental results presented here should provide useful guidance for designing Pt-based bimetallic HDO catalysts.

The high activity of oxide catalysts toward the oxygen reduction reaction (ORR) attracts unwanted interactions with other gaseous oxygen-containing species in air. Understanding the interaction between oxygen-containing species, mainly water and carbon dioxide, and oxides is important for many energy applications. However, the oxygen self-exchange process and the high-temperature operating conditions limit the investigation of these concurrent reactions. Here we report a direct observation of the effects of water and carbon dioxide on dissociation rates of ionically conducting catalysts, La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) and (La_0.8Sr_0.2)_0.95MnO_3±δ(LSM), using gas-phase isotope exchange. The concurrent heterogeneous reactions of oxygen and other oxygen-containing species on oxide catalysts can either promote or hinder oxygen dissociation rates, depending on the participation of lattice oxygen. LSCF appears to be much more active in exchange with these oxygen-containing species, while LSM shows relatively little exchange. Oxygen-containing species exhibit site-blocking effects and inhibit the reaction on LSCF. In contrast, water and CO₂ promote the oxygen dissociation rate on LSM, likely due to the prominence of homoexchange, where intermediate surface species play an important role. Our study provides insights into the reaction mechanism of oxygen dissociation and the effect of coexisting ambient air oxygen species.

The catalytic conversion of methanol (MeOH) and dimethyl ether (DME) into fuels and chemicals over zeolites (MTH process) is industrially emerging as an alternative route to conventional oil-derived processes. After 40 years of research, a detailed mechanistic understanding of the intricate reaction network is still not fully accomplished. The overall reaction is described as two competitive catalytic cycles, dominated by alkenes and arenes, which are methylated and cracked or dealkylated to form effluent products. Herein, we present the reaction of isobutene with methanol and DME as an efficient tool for measuring the relative formation rates of alkenes and arenes, and we provide detailed mechanistic insight into the hydrogen-transfer reaction. We provide experimental and theoretical evidence that manifest a strong competition of methylation and hydrogen transfer of isobutene by methanol, while methylation is substantially favored by DME. Experiments performed at higher conversion facilitate projection of the results to the product distribution obtained when using MeOH or DME as feedstock during the MTH reaction.

This paper describes a study of the nature and the accessibility of the acid sites in micromesoporous mordenite zeolites obtained by desilication and dealumination and analysis of their activity and selectivity in the hydroisomerization of n-hexane. Alkaline–acid, acid–alkaline–acid, and fluorination–alkaline–acid postsynthesis treatments were employed for the preparation of micromesoporous mordenites. The FTIR spectra of adsorbed d₃-acetonitrille, ²⁷Al MAS NMR, HR-TEM, and N₂ adsorption were used for quantitative analysis of the Brønsted and Lewis sites, the coordination of Al atoms, and the textural properties. The alkaline treatment causes desilication, preferably occurring along the crystal defects and resulting in the formation of a secondary mesoporous structure characterized by 5–20 nm cavities and the formation of extraframework (Al_Ex) species and terminal Si–OH groups. The Al_Ex species formed by hydrolysis of perturbed or dislodged framework Al easily restrict part of the pseudomonodimensional channel structure of mordenite. The subsequent removal of Al_Ex by mild acid leaching or simultaneous removal of Si and Al atoms by desilication of fluorinated zeolite result in a micromesoporous structure with a large number of unrestricted channel openings and lead to a large increase in the accessibility of OH groups for n-hexane. Thus, the sequential leaching treatments enable the formation of active acid sites in an environment of nonrestricted microporous channels with simultaneous enhancement of accessibility of the active sites and molecular transport. It is shown that the micromesoporous structure with high concentration of Brønsted sites of enhanced accessibility directs the hydroisomerization reaction toward high yields of branched isomers and shortening of the main 12-ring channels and that the larger numbers of channel openings result in an increase in selectivity, limiting nonselective subsequent cracking reactions.

We report the use of the ionic liquid tetrabutylphosphonium bromide as a solvent and catalyst for dehydration of diols to conjugated dienes. This system combines stability, high reaction rates, and easy product separation. A reaction mechanism for the model compound 1,2-hexanediol is proposed and experimentally corroborated. This particular mechanism allows for the selective formation of conjugated dienes, in contrast with purely acidic catalysis. Next, the reaction is also performed on various other diols. As a first application, we assessed the biobased production of 1,3-butadiene. With 1,4-butanediol as the starting material, a 94% yield of butadiene was reached at 100% conversion.

1,3,2-Diazaphospholene 1 catalyzes the conjugate transfer hydrogenation as well as the 1,4-hydroboration of α,β-unsaturated esters. The initial step for both processes involves a 1,4-hydrophosphination of the α,β-unsaturated esters to afford a phosphinyl enol ether. Subsequent cleavage of the P–O bond in the phosphinyl enol ether by ammonia-borane (AB) generates an enol intermediate which tautomerizes to saturated esters, while the P–O bond cleavage by HBpin via a formal σ-bond metathesis affords boryl enolate intermediate. The latter could undergo a further coupling reaction with nitriles to form substituted amino diesters or 1,3-imino esters, depending on α,β-unsaturated ester substrates. These catalytic reactions can also be performed in a one-pot manner, illustrating a protocol for metal-free catalytic C–C bond construction.

Nucleophilic sites on nanocarbon catalysts act as promoters for homolytic cleavage of aliphatic C–H bond. In this study, we report a hybrid catalyst composed of Mo₂C and nitrogen-doped onion-like carbon (NOLC) with enhanced capability for C–H bond activation in direct dehydrogenation (DH) reaction of ethylbenzene (EB). The enhanced activity of the Mo₂C/NOLC catalyst over unmodified NOLC in EB DH is attributable to the promoted C–H bond activation by Mo₂C, as characterized by the lower activation energy and the kinetic isotope effect using deuterated EB. Our XPS, XRD, and Raman spectroscopy results show that the hybrid catalyst is structurally robust under the reaction condition. The increase in nucleophilicity of the oxygen active sites in NOLC is evidenced by an overall shift of the O 1s peaks to lower binding energies after Mo₂C modification. The DFT calculation further provides mechanistic insights into the electron-transfer process from Mo₂C to the ketonic carbonyl groups.

Iron-PNP pincer complexes are efficient catalysts for the hydrogenation of aldehydes and ketones. A variety of hydrogenation mechanisms have been proposed for these systems, but there appears to be no clear consensus on a preferred pathway. We have employed high-level quantum chemical calculations to evaluate various mechanistic possibilities for iron-PNP catalysts containing either CH₂, NCH₃, or NH in the PNP linker. For all three catalyst types, we propose that the active species is a trans-dihydride complex. For CH₂- and NH-containing complexes, we predict a dihydride mechanism involving a dearomatization of the backbone. The proposed mechanism proceeds through a metal-bound alkoxide intermediate, in excellent agreement with experimental observations. Interestingly, the relative stability of the iron-alkoxide can explain why complexes with NCH₃ in the PNP linker are chemoselective for aldehydes, whereas those with CH₂ or NH in the linker do not show a clear substrate preference. As a general concept in computational catalysis, we recommend to employ known substrate selectivities as a diagnostic factor to evaluate the probability of proposed mechanisms.

The Pd/xantphos-catalyzed cross-coupling of amides and aryl halides is accelerated by cocatalytic metal triflate additives. A survey of nitrogen nucleophiles reveals improved yields for a variety of N-aryl amide products when Al(OTf)₃ is employed as a catalytic additive, with some exceptions. Initial rates of catalysis indicate that the Lewis acid acceleration is more pronounced when bromobenzene (PhBr) is used in comparison with iodobenzene (PhI). The observation of an aryl halide dependence on rate and various qualitative kinetic experiments are consistent with a mechanism in which ligand exchange of halide for amide (“transmetalation”) is turnover limiting. The mechanism may be different depending on whether PhBr or PhI is used as a coupling partner. Oxidative addition complexes (xantphos)Pd(Ph)(X) (X = Br, I; xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), likely intermediates in catalysis, have been prepared; their differing interactions with Yb(OTf)₃ in solution resemble the halide dependence of the catalytic mechanism, which we propose originates from a reversible Lewis acid mediated halide abstraction during catalysis.

Nanostructured CuCo₂S₄, a mixed metal thiospinel, is found to be a benchmark electrocatalyst for oxygen evolution reaction (OER) in this study with a low overpotential, a low Tafel slope, a high durability, and a high turnover frequency (TOF) at lower mass loadings. Nanosheets of CuCo₂S₄ are realized from a hydrothermal synthesis method in which the average thickness of the sheets is found to be in the range of 8–15 nm. Aggregated nanosheets form a highly open hierarchical structure. When used as an electrocatalyst, CuCo₂S₄ nanosheets offer an overpotential value of 310 mV at a 10 mA cm^–2 current density, which remains consistent for 10000 measured cycles in a 1 M KOH electrolyte. A chronoamperometric study reveals constant oxygen evolution for 12 h at a 10 mV s^–1 scan rate without any degradation of the activity. Furthermore, the calculated mass activity of the CuCo₂S₄ electrocatalyst is found to be 14.29 A/g and to afford a TOF value of 0.1431 s^–1 at 310 mV at a mass loading of 0.7 mg cm^–2. For comparison, nanostructures of Co₃S₄ and Cu_0.5Co_2.5S₄ have been synthesized using a similar method followed for CuCo₂S₄. When compared to the OER activities among these three thiospinels and standard IrO₂, CuCo₂S₄ nanosheets offered the highest OER activities at the same mass loading (0.7 mg/cm²). Extensive X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses for a mechanistic study reveal that introduction of Cu into the Co₃S₄ lattice enhances the oxygen evolution and kinetics by offering Cu²⁺ sites for utilitarian adsorption of OH, O, and OOH reactive species and also by offering a highly active high-spin state of octahedral Co³⁺ for OER catalysis.

A route was developed for the synthesis of diesel and jet fuel range C₉ and C₁₀ alkanes with furfural and angelica lactone, which can be obtained from hemicellulose and cellulose. It was found that angelica lactone is more reactive than levulinic acid or its other derivates in the aldol condensation with furfural. Among the investigated catalysts, Mn₂O₃ was found to be the most active and was very stable for the aldol condensation of furfural and angelica lactone. Over Mn₂O₃, a high carbon yield of C₁₀ oxygenates (about 96%) can be achieved by the aldol condensation of furfural and angelica lactone under mild conditions (353 K, 4 h). By the hydrogenation and hydrodeoxygenation of the aldol condensation product over the Pd/C and Pd-FeO_x/SiO₂ catalysts, high carbon yields (∼96%) of C₉ and C₁₀ alkanes were obtained.

The ability to generate nanoscale zeolites and direct their assembly into hierarchical structures offers a promising way to maximize their diffusion-dependent catalytic performance. Herein, we report an orientated assembly strategy to construct hierarchical architectures of silicoaluminophosphates (SAPOs) by using prefabricated nanocrystallites as a precursor. Such a synthesis is enabled by interrupting the dry gel conversion process to prepare nanocrystallites, as crystal growth is shown to proceed predominantly by particle attachment. The orientation of assembly can be controlled to form either a three-dimensional, spongelike morphology or a two-dimensional “house-of-cards” structure, by modifying the additives. Structures with a high degree of control over crystal size, shape, architecture, pore network, and acidic properties are achieved. This versatile technique avoids the more tedious and expensive templating routes that have been proposed previously. The catalytic performance for the hydroisomerization of n-heptane was evaluated for a series of Pt-supported catalysts, and a record isomer yield (79%) was attained for a catalyst with spongelike architecture. The hierarchical architecture influences isomer selectivity for two reasons: expanding the intrinsic-reaction-controlled regime to be able to work at higher temperatures or conversion levels, and enhancing mass transport to reduce cracking of dibranched isomers. Such an acidity–diffusivity interplay indicates that strong acidity favors isomerization operating at temperatures away from the diffusion-limited regime, while crystal size and pore connectivity are key factors for enhancing diffusion. The proposed materials offer tremendous opportunities to realize hierarchical catalyst designs that work under optimal operating conditions.

Site selective C–H oxidation of N-alkylamides and phthalimides with aqueous hydrogen peroxide catalyzed by manganese complexes is described. These catalysts are shown to exhibit substantially improved performance in product yields and substrate scope in comparison with their iron counterparts. The nature of the amide and imide group and of the N-alkyl moiety are shown to be effective tools in order to finely tune site selectivity between proximal (adjacent to the nitrogen) and remote C–H bonds on the basis of steric, electronic, and stereoelectronic effects. Moreover, formation of the α-hydroxyalkyl product in good yield and with excellent product chemoselectivity was observed in the reactions of the pivalamide and acetamide derivatives bearing an α-CH₂ group, pointing again toward an important role played by stereoelectronic effects and supporting the hypothesis that these oxidations proceed via hydrogen atom transfer (HAT) to a high-valent manganese–oxo species. Good product yields and mass balances are obtained in short reaction times and under mild experimental conditions when relatively low loadings of an electron-rich manganese catalyst are used. The potential utility of these reactions for preparative purposes is highlighted in the site-selective oxidation of the pivalamide and phthalimide derivatives of substrates of pharmaceutical interest.

Electrochemical high-temperature oxygen reduction and evolution play an important role in energy conversion and generation using solid oxide electrochemical cells. First-series Ruddlesden–Popper (R-P) oxides (A₂BO₄) have emerged as promising electrocatalysts for these reactions due to their suitable mixed ionic and electronic conductivities. However, a detailed understanding of the factors that govern their performance is still elusive, making their optimization challenging. In the present work, a systematic theoretical study is used to investigate the underlying factors that control the process of surface oxygen exchange, which governs oxygen reduction and evolution on these oxides. The effects of A- and B-site composition and surface termination of these oxides on their activities are elucidated. Among the different compositions, Co-based, B-site-terminated R-P oxides are predicted to exhibit the highest activity due to providing the best compromise between the energetics associated with oxygen dissociation and surface oxygen vacancy formation. A “volcano”-type relation between the calculated rates for surface oxygen exchange and O₂ binding energy on a surface oxygen vacancy is found, suggesting the O₂ binding energy might be used as an activity descriptor to identify R-P oxides with optimized performance. These findings shed light on the factors that govern the reported experimental behaviors of these oxides and lay the groundwork for the development of predictive models to design optimal mixed ionic and electronic conducting oxides for high-temperature oxygen reduction and evolution.

A series of mono(amidate) Ta and Nb complexes with varying steric and electronic properties were synthesized. These complexes were screened as precatalysts for the hydroaminoalkylation of alkenes with secondary amines. Sterically demanding mono(amidate) Ta complexes were determined to be the most effective precatalysts. Isotopic labeling and kinetic studies were undertaken in an effort to elucidate the mechanism. The reaction was shown to be dependent upon catalyst and alkene concentration while being zero order in amine concentration. Mechanistic probes for radical species support a two-electron mechanism. Bis(amidate) species of Ta and Nb were also synthesized, with metallaaziridine formation observed for both metals. Insertion of acetonitrile into the reactive M–C bond yielded a representative five-membered metallacycle. Off-cycle equilibria and catalyst dormant states have been identified as areas for future catalyst development efforts.

The preparation and isolation of a family of Ru–Cl complexes containing the deprotonated anionic tridentate meridional ligand (1Z,3Z)-N¹,N³-di(pyridin-2-yl)isoindoline-1,3-diimine (Hbid) and 1,3-di(2-pyridyl)benzene) (Hdpb), namely, [Ru(bid)(acac)Cl], 1d, [Ru(bid)(6,6′-Me₂-bpy)Cl], 1e, trans-[Ru(bid)(py)₂Cl], 2, [Ru(dpb)(bpy)Cl], 3a, and [Ru(dpb)(4,4′-(COOEt)₂-bpy)Cl], 3b, are reported. All these complexes have been thoroughly characterized in solution by NMR spectroscopy and for 1d and 1e by single-crystal X-ray diffraction analysis. Furthermore, the redox properties of all complexes have been investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The capacity of the various complexes to catalyze hydrogenative CO₂ reduction was also investigated. Compound 1e is the best catalyst, achieving initial turnover frequencies above 1000 h^–1. Kinetic analysis identifies a relationship between Ru(III/II) couple redox potentials and initial turnover frequencies. Finally, DFT calculations further characterize the catalytic cycle of these complexes and rationalize electronic and steric effects deriving from the auxiliary ligands.

The catalytic nanopatterning of few-layer graphene (FLG) sheets using metallic nanoparticles as catalytic “nanogouges” is a promising method for fabricating graphene nanoribbons. However, in the absence of in situ observations of the active nanoparticles during the catalytic process, a unified model of the channeling mechanism is unavailable. On the basis of a real-time TEM investigation of iron nanoparticle patterning of FLG, this study addresses key aspects of the channeling mechanism. As the catalytic reactions take place at temperatures at which the active nanoparticles present a melted superficial layer, the adhesion forces at the nanoparticle/FLG interface were found to have a crucial role in defining their faceting geometry. Mono- and multifaceted frontal geometries are induced by the interaction with the vertical FLG edges, and only such faceting arrangements can support a controlled anisotropic channeling. When the channeling direction is changed, nanoparticles go through a process of surface rearrangement that aims at rebuilding a faceting geometry in equilibrium with the FLG edge. The melted superficial layer appears as the main nanoparticle region that supports the dissolution of FLG edges, and a concentration gradient is moving the dissolved carbon atoms from the interface regions toward the rear side of the nanoparticles.

Ruthenium-catalyzed selective hydroboration of styrenes and aliphatic olefins with pinacolborane (HBpin) is reported. This efficient transformation provided products with exclusive anti-Markovnikov selectivity, and this hydroboration protocol is compatible with olefins having electronic and steric divergence as well as diverse functional groups. Hydroboration occurred at room temperature under solvent-free conditions with minimal catalyst load (0.05 mol %) and provided high TON (>1980; >990 per Ru). Mechanistic studies confirmed the involvement of intermediate [{(η⁶-p-cymene)RuCl}₂(μ-H-μ-Cl)] (2). A catalytic cycle including a mononuclear ruthenium intermediate is proposed. The rationale for observed anti-Markovnikov selectivity is provided from reversible 1,3-hydride transfer leading to the regioselective 1,2-insertion on olefins.

Highly ordered mesoporous Fe₂O₃–ZrO₂ mixed bimetal oxides (FeZr) without any additional chemical promoters were first applied to produce the value-added hydrocarbons by CO hydrogenation through Fischer–Tropsch synthesis (FTS) reaction of syngas. To enhance a catalytic activity and structural stability, an irreducible ZrO₂ as a structural promoter was incorporated in the ordered mesoporous Fe₂O₃ structures with a different Zr/Fe molar ratio from 0 to 1 prepared by using a hard template of KIT-6. When an optimal amount of zirconia (Zr/Fe molar ratio = 0.25) was incorporated in the ordered mesoporous Fe₂O₃ frameworks, the catalytic activity was significantly improved and almost 10 times higher than the mesoporous monometallic Fe₂O₃. The highly ordered mesoporous structures were stably preserved even under reductive FTS reaction conditions. The ordered mesoporous FeZr catalysts showed a higher C₅+ selectivity even at a higher CO conversion above 80%. This improved catalytic activity and stability on the optimized FeZr catalyst were mainly attributed to the facile formation of active iron carbide species such as the stable χ-Fe₅C₂ with insignificant structural collapses through a formation of strongly interacted iron nanoparticles with the ZrO₂ structural promoter with a suppressed inactive coke deposition in the highly ordered FeZr mesopores.

HY zeolite-supported Rh(CO)₂ complexes were used as precursors for the surface-mediated synthesis of Rh(NO)₂ species. The results of FTIR, EXAFS, and mass spectrometry measurements, as well as DFT calculations, show that the replacement of the CO ligands in the Rh(CO)₂ complexes by NO is a facile substitution process which is not affected by the Si/Al ratio of the zeolite support used. The Rh(NO)₂ complexes thus formed are site-isolated 14-electron species with a Rh–N bond distance of 1.77 Å, a N–Rh–N angle of ∼104°, and NO ligands significantly deviating from a linear configuration (Rh–N–O angle ∼148°). These species exhibit a characteristic set of well-defined ν_NO bands at 1855 and 1779 cm^–1 in their FTIR spectra and have an additional empty d orbital at the rhodium center allowing for coordination of a third electron-donating ligand. Therefore, the Rh(NO)₂ species react with C₂H₄ to form 16-electron Rh(NO)₂(C₂H₄) species which are stable in the presence of gas-phase C₂H₄ and can be further converted into Rh(NO)₂(C₂H₅) complexes by addition of H₂. The Rh(NO)₂/HY30 material catalyzed both C₂H₄ hydrogenation and dimerization reactions at room temperature with TOFs of 0.01 and 6.7 × 10^–3 s^–1 at steady state, respectively. During these processes, the Rh sites remain monodispersed. An inverse kinetic isotope effect was observed for both reactions, thus underlining the similarities of the catalytic properties of the supported Rh(NO)₂ species examined and molecular organometallic Rh complexes in solution. This is a notable example demonstrating that Rh dinitrosyl complexes anchored on a solid support can catalyze hydrocarbon reactions.

myo-Inositol belongs to the vitamin B group (vitamin B8) and is widely used in the drug, cosmetic, and food and feed industries. It is produced by acid hydrolysis of phytate, but this method suffers from costly feedstock and serious phosphorus pollution. Here a four-enzyme pathway containing thermophilic sucrose phosphorylase, phosphoglucomutase, inositol 1-phosphate synthase, and inositol monophosphatase was designed to convert sucrose to inositol and fructose. To enable the use of enzymes with different optimal temperatures and thermostabilities, we developed a thermal cycling cascade biocatalysis that can selectively add less-thermostable sucrose phosphorylase immobilized on cellulose-containing magnetic nanoparticles into the cold enzyme cocktail or remove it from the hot enzyme cocktail by using a magnetic field (ON/OFF) switch. A series of exergonic reactions push the overall reaction forward, resulting in a high product molar yield (0.98 mol of inositol/mol of sucrose). This cascade biocatalysis platform could open a door to the large-scale production of less-costly inositol and upgrade sucrose to a value-added nutraceutical and functional sweetener.

Cobalt phosphate is considered to be one of the most active catalysts for the oxygen evolution reaction (OER) in neutral or near-neutral pH media, but only a few transition-metal phosphates are investigated in alkaline media, probably due to their poor intrinsic electrical conductivity and/or tendency to aggregate. Herein, in situ-formed cobalt phosphate decorated with N-doped graphitic carbon was prepared using phosphonate-based metal–organic frameworks (MOFs) as the precursor. It can serve as a highly active OER catalyst in alkaline media, affording a current density of 10 mA cm^–2 at a small overpotential of 215 mV on the Ni foam. A combination of X-ray absorption spectroscopy and high-resolution XPS elucidates the origin of the high activity. Our observations unveil that cobalt diphosphate having the distorted metal coordination geometry with long Co–O and Co–Co distances is mainly responsible for the high OER activity. These results not only demonstrate the potential of a low-cost OER catalyst derived from phosphonate-based MOF but also open a promising avenue into the exploration of highly active and stable catalysts toward replacing noble metals as oxygen evolution electrocatalysts.

Catalysts that are able to reduce carbon dioxide under mild conditions are highly sought after for storage of renewable energy in the form of a chemical fuel. This study describes a systematic kinetic and thermodynamic study of a series of cobalt and rhodium bis(diphosphine) complexes that are capable of hydrogenating carbon dioxide to formate under ambient temperature and pressure. Catalytic CO₂ hydrogenation was studied under 1.8 and 20 atm of pressure (1:1 CO₂/H₂) at room temperature in tetrahydrofuran with turnover frequencies (TOF) ranging from 20 to 74 000 h^–1. The catalysis was followed by ¹H and ³¹P NMR spectroscopy in real time under all conditions to yield information about the rate-determining step. The cobalt catalysts displayed a rate-determining step of hydride transfer to CO₂, while the hydrogen addition and/or deprotonation steps were rate limiting for the rhodium catalysts. Thermodynamic analysis of the complexes provided information on the driving force for each step of catalysis in terms of the catalyst hydricity (ΔG°_H^–), acidity (pK_a), and free energy for H₂ addition (ΔG°_H2). Linear free-energy relationships were identified that link the kinetic activity for catalytic hydrogenation of CO₂ to formate with the thermodynamic driving force for the rate-limiting steps of catalysis. The catalyst exhibiting the highest activity, Co(dmpe)₂H, was found to have hydride transfer and hydrogen addition steps that were each downhill by approximately 6 to 7 kcal mol^–1, and the deprotonation step was thermoneutral. This indicates the fastest catalysts are the ones that most efficiently balance the free energy relationships of every step in the catalytic cycle.

Atomic-level identification of carbon intermediates under reaction conditions is essential for carbon-related heterogeneous catalysis. Using the in operando technique of near-ambient-pressure X-ray photoelectron spectroscopy, we have identified various carbon intermediates during the thermal decomposition of CH₄ on Ni(111), including *CH, *C₁/Ni₃C, *C_n (n ≥ 2), and clock-reconstructed Ni₂C at different temperature regions (300–900 K). These “reactive” carbon precursors can either react with probing molecules such as O₂ at room temperature or be etched away by CH₄. They can also develop into graphene flakes under controlled conditions: a temperature between 800 and 900 K and a suitable CH₄ pressure (10^–3–10^–1 mbar, depending on temperature). The growth rate of graphene is significantly restrained at higher CH₄ pressures, due to the accelerated etching of its carbon precursors. The identification of in operando carbon intermediates and the control of their evolution have great potential in designing heterogeneous catalysts for the direct conversion of methane. The observed carbon aggregation/etching equilibrium reveals an underlying mechanism in coking prevention and in the fabrication of large-area single-crystal graphene, where the suppression of seeding density and etching up of small grains are required.

Staged biomass pyrolysis or condensation of the pyrolysis vapor generates less complex and concentrated liquid product streams, which provide a very promising route to produce value-added chemicals. Acetol is one of the major light oxygenates in fractionated bio-oil. Here we report an efficient one-pot conversion of acetol to lactic acid, a key platform chemical and an important monomer of biodegradable polymer, in aqueous phase over a bifunctional dealuminated Sn-Beta supported gold catalyst. Under relatively mild conditions (393 K, 1.9 MPa N₂ + 0.1 MPa O₂), 93.4% acetol conversion and 73.2% selectivity toward lactic acid were achieved. On the basis of measured rate constants, the reaction pathway likely proceeds via kinetically relevant oxidation of acetol to form pyruvaldehyde, followed by hydration and 1,2-hydride shift (internal Meerwein–Ponndorf–Verley reduction and Oppenauer oxidation) on Sn-Lewis sites to produce lactic acid.

Whereas the metal-catalyzed C(sp²)–N cross-coupling of cyclopropylamine with aryl electrophiles represents an attractive route to pharmaceutically relevant N-arylcyclopropylamines, few catalysts that are capable of effecting such transformations have been identified. Herein, the nickel-catalyzed C(sp²)–N cross-coupling of cyclopropylamine and related nucleophiles, including ammonium salts, with (hetero)aryl (pseudo)halides is reported for the first time, with the demonstrated scope of reactivity exceeding that displayed by all previously reported catalysts (Pd, Cu, or other). Our preliminary efforts to effect the N-arylation of cyclopropylamine with (hetero)aryl chlorides at room temperature by use of (L)NiCl(o-tolyl) precatalysts (L = PAd-DalPhos, C1; L = JosiPhos CyPF-Cy, C2) were unsuccessful, despite the established efficacy of C1 and C2 in transformations of other primary alkylamines. However, systematic modification of the ancillary ligand (L) structure enabled success in such transformations, with crystallographically characterized (L)NiCl(o-tolyl) precatalysts incorporating o-phenylene-bridged bisphosphines featuring phosphatrioxaadamantane and PCy₂ (L = L3, CyPAd-DalPhos; C3), P(o-tolyl)₂ and P(t-Bu)₂ (L = L4; C4), or PCy₂ and P(t-Bu)₂ (L = L5; C5) donor pairings proving to be particularly effective. In employing the air-stable precatalyst C3 in cross-couplings of cyclopropylamine, substituted electrophiles encompassing an unprecedentedly broad range of heteroaryl (pyridine, isoquinoline, quinoline, quinoxaline, pyrimidine, purine, benzothiophene, and benzothiazole) and (pseudo)halide (chloride, bromide, mesylate, tosylate, triflate, sulfamate, and carbamate) structures were employed successfully, in the majority of cases under mild conditions (3 mol % of Ni, 25 °C). Preliminary studies also confirmed the ability of C3 to effect the N-arylation of cyclopropanemethylamine hydrochloride and cyclobutylamine hydrochloride under similar conditions. A notable exception in this chemistry was observed specifically in the case of electron-rich aryl chlorides, where the use of C4 in place of C3 proved more effective. In keeping with this observation, catalyst inhibition by 4-chloroanisole was observed in the otherwise efficient cross-coupling of cyclopropylamine and 3-chloropyridine when using C3. Competition studies involving C3 revealed a (pseudo)halide reactivity preference (Cl > Br, OTs).

The small-pore KFI-type zeolite was synthesized via the hydrothermal conversion of zeolite Y with Na⁺ and K⁺ ions without using an organic structure-directing agent (OSDA). The effects of alkali-metal ions and hydroxide ion on the crystallization of KFI were individually investigated by introducing both hydroxide and nitrate salts into synthesis media. The zeolite KFI synthesized under the optimized conditions was copper ion exchanged and then applied for selective catalytic reduction of NO_x with an NH₃ (NH₃-SCR) reaction. Cu-KFI was found to exclusively contain isolated copper ions up to very high loading (Cu/Al₂ = 75%) on the basis of the Cu K-edge extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), ultraviolet visible near-infrared spectroscopy (UV–vis–NIR), and temperature-programmed reduction by H₂ (H₂-TPR) analyses. Interestingly, Cu-SSZ-13 and Cu-KFI have almost identical activation energies for the NH₃-SCR reaction as well as the reduction temperature of “hydrated” copper ions by H₂, indicating the presence of similar active sites on both catalysts. After severe hydrothermal aging at 800 °C for 16 h, Cu-KFI substantially maintained its structural integrity, which is remarkably stable in comparison with Cu-chabazite synthesized from organic-free media. The NH₃-SCR activity test under realistic conditions showed that Cu-KFI with high Cu loading has activity comparable to that of Cu-SSZ-13 even after hydrothermal aging. All combined results evidently confirm that the zeolite-based catalyst prepared under organic-free conditions can also exhibit excellent hydrothermal stability, which is attributed to the high crystallinity of zeolite and the presence of only isolated copper ions.

Rational design of the microstructure and intrinsic active sites of nitrogen-doped carbon (NC) materials to achieve highly efficient oxygen reduction reaction (ORR) electrocatalysts is extremely important for many renewable energy devices. Herein, we develop a metal–organic framework (MOF) derived metal-free NC material via a simple and low-cost NH₃ activation strategy. With NH₃ activation, the ORR catalytic performance of the MOF-derived material shows a great promotion. The material outperforms commercial Pt/C catalyst toward ORR catalysis in alkaline media with ∼28 mV higher half-wave potential. This amazing ORR performance might be attributed to its large specific surface area, hierarchical porosity, and full exposure of valid N species (mainly graphitic-N) to the ORR, which result from the facile NH₃ activation.

Methanol conversion over zeolites with different topologies (H-ZSM-5, H-SSZ-13, and H-MOR) was studied using solid-state NMR spectroscopy and gas chromatrography mass spectroscopy (GC-MS). Host–guest interactions between active hydrocarbon pool (HP) species and zeolite framework (Brønsted acid/base site) were observed, and the supramolecular reaction centers (SMCs) generated by the interactions were unambiguously identified by ¹³C–²⁷Al double-resonance NMR. The internuclear spatial interaction/proximity between the ¹³C nuclei (associated with HP species) and the ²⁷Al nuclei (associated with Brønsted acid/base site) was analyzed and compared over the three zeolites. The product shape selectivity of zeolites greatly influences the catalytic performance that can be linked to the nature of HP species and the host–guest interactions. Closer spatial proximity and stronger interaction between methylbenzenes (MBs) and Brønsted acid/base sites were observed over H-SSZ-13 and H-MOR zeolites, which facilitate aromatic-based reaction routes and rationalize the higher selectivity to ethene on the two catalysts. This leads to rapid deactivation at high temperature due to coke deposition on the active sites caused by the evolution of active MBs. For H-ZSM-5, the lesser amount of retained MBs and their weaker interactions with the active sites at high temperature cause the aromatic-based reactions to be insignificant and lead to the prevalence of alkene-based and carbocation-involved reactions, which are responsible for the high resistance of H-ZSM-5 to deactivation. In contrast, at lower temperature, the aromatic-based reaction route is favored with the MBs-composed SMCs prevailing. The distribution of the carbonaceous species in deactivated catalysts was revealed by host–guest interactions.

A copper-catalyzed tandem carboarylation/cyclization of alkynyl phosphonates with diaryliodonium salts is reported. The reaction gives straightforward access to valuable cyclic enol phosphonates in good yields under mild conditions. This transformation entails an initial chemoselective arylation of the alkyne followed by an intramolecular trapping of an intermediate vinyl cation by the phosphoryl group. Observation of β-aryl rearrangements across the double bond in intermediates generated from 1,2-diaryl alkynes support the intermediacy of a vinyl cation.

Metal-free catalysis for electrocatalytic hydrogen evolution from water is very demanding for the production of sustainable and clean fuel. Herein, we report the synthesis of a porphyrin-based metal-free covalent organic polymer (TpPAM) through a simple condensation between triformyl phloroglucinol (Tp) and 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin (PAM). The as-prepared porous TpPAM exhibited superior activity for the hydrogen evolution reaction (HER) current density of 10 mA cm^–2 at a low overpotential of 250 mV and a small Tafel slope of 106 mV decade^–1, which are better than those of related metal-free electrocatalysts. The high HER activity of TpPAM was investigated in-depth via theoretical density functional theory (DFT) calculations. The theoretical findings were correlated with the experimental results, and these were in good agreement for high HER catalytic efficiency of the porous TpPAM polymer. The Faradaic efficiency of the TpPAM-based electrode was found to be 98%, which is very close to the ideal value of 100%, reflecting its potential for practical implementation. Moreover, the as-synthesized catalyst showed good stability by retaining 91% of the initial current density after 1000 cycles.

Plasmonic nanoparticles are exciting and promising candidates for light-activated catalysis. We report herein the use of plasmonic nanocubes for the activation of molecular hydrogen and the hydrogenation of ketones and aldehydes via visible light irradiation at 405 nm, corresponding to the position of the plasmon band of the nanocubes, at 80 °C. Only 1 atm of molecular hydrogen is required to access, using catalytic amounts of silver, primary, and secondary alcohols, with complete chemoselectivty for C═O over C═C reduction. The resulting catalytic system was studied over a scope of 12 compounds. Exposure to other wavelengths, or absence of light failed to provide activity, thus proving a direct positive impact of the plasmonic excitation to the catalytic activity. By varying the irradiation intensity, we studied the relationship between plasmon band excitation and catalytic activity and propose a potential reaction mechanism involving plasmon-activated hot electrons. This study expands the scope of reactions catalyzed by free-standing plasmonic particles and sheds light on H₂ activation by silver surfaces.

The thermodynamic and structural factors that influence the redox properties of an extensive set of tungsten–alkylidyne complexes (W(CR)L₄X) are analyzed by combining synthesis, electrochemistry, and computational modeling based on free energy calculations of oxidation potentials at the density functional theory level. The observed linear correlations among oxidation potentials, HOMO energies, and gas-phase ionization energies are found to be consistent with the approximately constant solvation free energy differences between reduced and oxidized species over the complete set. The W–X bond length, trans to the alkylidyne ligand, is found to be a good descriptor of the positioning of the key frontier orbitals that regulate the redox properties of the complexes.

Three-dimensional macroporous carbon materials with hierarchical pore structures (3D MPC) have wide applications, but the scale-up synthesis is limited by the cumbersome procedures of template formation and removal. Herein, we show that NaCl crystallites, which form in situ in a lyophilizing process of a NaCl solution containing a carbon precursor and are removable simply through water washing, can act as templates to grow 3D MPC materials with graphene-like ultrathin and mesoporous walls through pyrolitic carbonization. Further, by use of a nitrogen (N)-rich polymer (polyvinylpyrrolidone, PVP) as the carbon precursor and introduction of Fe salt in the precursor, an MPC catalyst with high Fe/N doping content is achieved due to the NaCl crystallites serving as confining agents to simultaneously prevent the large weight loss and N evaporation, a severe problem in usual pyrolytic syntheses of Fe-N-C catalysts. Benefiting from the mass transport convenience of the macropores as indicated by the impedance spectroscopy results, the Fe/N-doped 3D MPC exhibits high catalytic performance toward the oxygen reduction reaction. The dual functionality, facile formation and removal, and reusability of NaCl make the present method a promising way to gain cost-effective porous Fe-N-C catalysts.

A series of P-chirogenic Xantphos ligands and related diaryl ether diphosphines have been synthesized by a modification of the well-established Jugé method. The approach consists of the in situ deboranation of the chiral ephedrine-based phosphinite before the P–C coupling takes place. The stereochemical integrity of the stereocenters of the diphosphines during synthesis, long-time storage, and catalytic application was evaluated. In the rhodium-catalyzed asymmetric hydrogenation of isophorone as a model substrate for industrially relevant prostereogenic enones with some of the diphosphines, almost complete conversion, high chemoselectivity, and 96% ee were achieved.

Light alkenes oligomerization, performed in the presence of heterogeneous acid catalysts, is an interesting alternative for the production of clean liquid fuels. The process, when catalyzed by zeolites, is flexible and can be directed to the formation of oligomers in the gasoline, jet fuel, or diesel range by adjusting the reaction conditions and the zeolite’s structure. Herein we show how reducing the crystal size of large-pore Beta zeolites down to 10–15 nm and controlling the number and strength distribution of their Brønsted acid sites leads to highly active and stable catalysts, selective to true oligomers within the naphtha and, especially, the diesel range. The shorter diffusion path lengths in the smaller crystallites and the reduced Brønsted acid site density of the two nanosized beta zeolites (10–15 nm) synthesized with Si/Al = 15 lead to 1-pentene conversion above 80% during the 6 h time on stream (TOS) at a space time (W/F) of 2.8 g·h·mol^–1. This value is higher than the olefin conversion obtained for a commercial nanobeta (30 nm) at a 3-fold space time of 9.1 g·h·mol^–1.

Electrochemical water splitting to produce hydrogen bears a great commitment for future renewable energy conversion and storage. By employing an in situ chemical vapor deposition (CVD) process, we prepared a bimetal (Ni and Mo) sulfide-based hybrid nanowire (NiS₂/MoS₂ HNW), which was composed of NiS₂ nanoparticles and MoS₂ nanoplates, and revealed that it is an efficient electrocatalyst for the hydrogen evolution reaction (HER) over a wide pH range due to the collective effects of rational morphological design and synergistic heterointerfaces. On a simple glassy carbon (GC) electrode, NiS₂/MoS₂ HNW displays overpotentials at −10 mA cm^–2 catalytic current density (η₁₀) of 204, 235, and 284 mV with small Tafel slopes of 65, 58, and 83 mV dec^–1 in alkaline, acidic, and neutral electrolyte, respectively, exhibiting pH-universal-efficient electrocatalytic HER performance, which is comparable to the recently reported state-of-the-art sulfide-based HER electrocatalysts. Theoretical calculations further confirm that the advantage of all-pH HER activity of NiS₂/MoS₂ originates from the enhanced dissociation of H₂O induced by the formation of lattice interfaces of NiS₂–MoS₂ heterojunctions. This work can pave a valuable route for designing and fabricating inexpensive and high-performance electrocatalysts toward HER over a wide pH range.

Glucose oxidase has wide applications in the pharmaceutical, chemical, and food industries. Many recent studies have enhanced key properties of this enzyme using directed evolution, yet without being able to reveal why these mutations are actually beneficial. This work presents a synergistic combination of experimental and computational methods, indicating how mutations, even when distant from the active site, positively affect glucose oxidase catalysis. We have determined the crystal structures of glucose oxidase mutants containing molecular oxygen in the active site. The catalytically important His516 residue has been previously shown to be flexible in the wild-type enzyme. The molecular dynamics simulations performed in this work allow us to quantify this floppiness, revealing that His516 exists in two states: catalytic and noncatalytic. The relative populations of these two substates are almost identical in the wild-type enzyme, with His516 readily shuffling between them. In the glucose oxidase mutants, on the other hand, the mutations enrich the catalytic His516 conformation and reduce the flexibility of this residue, leading to an enhancement in their catalytic efficiency. This study stresses the benefit of active site preorganization with respect to enzyme conversion rates by reducing molecular reorientation needs. We further suggest that the computational approach based on Hamiltonian replica exchange molecular dynamics, used in this study, may be a general approach to screening in silico for improved enzyme variants involving flexible catalytic residues.

Photocatalytic ozonation of wastewater pollutants by sunlight is a highly attractive technology close to real application. Understanding this process on the atomic scale and under realistic working conditions is challenging but vital for the rational design of catalysts and photocatalytic decontamination systems. Here we study two highly active C₃N₄ photocatalysts (bulk C₃N₄ and a nanosheet-structured C₃N₄) under simultaneous visible-light irradiation and O₃ bubbling in water by in situ EPR spectroscopy coupled with an online spin-trapping technique. The photoexcitation of electrons to the conduction band (CB-e^–), their further trapping by dissolved O₂ and O₃, and the evolution of reactive oxygen species (ROS) have been semiquantitatively visualized. A dual role of O₃ in boosting the CB-e^– to ^•OH conversion is confirmed: (i) an inlet 2.1 mol % O₃/O₂ gas mixture can trap about 2–3 times more CB-e^– upon aqueous C₃N₄ suspension than pure O₂ and further produce ^•OH by a robust ^•O₃^–-mediated one-electron-reduction pathway (O₃ → ^•O₃^– → HO₃^• → ^•OH); (ii) O₃ can readily take CB-e^– back from ^•O₂^– to form ^•O₃^–, thus blocking the inefficient H₂O₂-mediated three-electron-reduction route (O₂ → ^•O₂^– → HO₂^• → H₂O₂ → ^•OH) but further strengthening the ^•O₃^–-mediated pathway. In the presence of 2.1 mol % O₃/O₂, the ^•OH yield increases by 17 and 5 times, and consequently, the mineralization rate constant of oxalic acid increases by 84 and 41 times over bulk C₃N₄ and NS C₃N₄, respectively. This work presents an attractive opportunity to boost the yield of ROS species (^•OH) for water purification by visible-light-driven photocatalysis and provides a powerful tool to monitor complex photocatalytic reactions under practical conditions.

Succinic acid is a biomass-derived platform chemical that can be catalytically converted in the aqueous phase to 1,4-butanediol (BDO), a prevalent building block used in the polymer and chemical industries. Despite significant interest, limited work has been reported regarding sustained catalyst performance and stability under continuous aqueous-phase process conditions. As such, this work examines Ru-Sn on activated carbon (AC) for the aqueous-phase conversion of succinic acid to BDO under batch and flow reactor conditions. Initially, powder Ru-Sn catalysts were screened to determine the most effective bimetallic ratio and provide a comparison to other monometallic (Pd, Pt, Ru) and bimetallic (Pt-Sn, Pd-Re) catalysts. Batch reactor tests determined that a ∼1:1 metal weight ratio of Ru to Sn was effective for producing BDO in high yields, with complete conversion resulting in 82% molar yield. Characterization of the fresh Ru-Sn catalyst suggests that the sequential loading method results in Ru sites that are colocated and surface-enriched with Sn. Postbatch reaction characterization confirmed stable Ru-Sn material properties; however, upon a transition to continuous conditions, significant Ru-Sn/AC deactivation occurred due to stainless steel leaching of Ni that resulted in Ru-Sn metal crystallite restructuring to form discrete Ni-Sn sites. Computational modeling confirmed favorable energetics for Ru-Sn segregation and Ni-Sn formation at submonolayer Sn incorporation. To address stainless steel leaching, reactor walls were treated with an inert silica coating by chemical vapor deposition. With leaching reduced, stable Ru-Sn/AC performance was observed that resulted in a molar yield of 71% BDO and 15% tetrahydrofuran for 96 h of time on stream. Postreaction catalyst characterization confirmed low levels of Ni and Cr deposition, although early-stage islanding of Ni-Sn will likely be problematic for industrially relevant time scales (i.e., thousands of hours). Overall, these results (i) demonstrate the performance of Ru-Sn/AC for aqueous phase succinic acid reduction, (ii) provide insight into the Ru-Sn bimetallic structure and deactivation in the presence of leached Ni, and (iii) underscore the importance of compatible reactor metallurgy and durable catalysts.

The copper-catalyzed hydroarylation of internal, unsymmeric alkynes is presented. Trisubstituted alkenes are obtained as single diastereomers in good to excellent yields and excellent regioselectivities. The scope of the reaction is presented with respect to alkyne and aryl iodide coupling partners. Initial mechanistic experiments indicate a hydrocupration event followed by a two-electron oxidative addition/reductive elimination pathway.

A plasmon and upconversion enhanced broadband photocatalyst based on Au nanoparticle (NP) and NaYF₄:Yb³⁺, Er³⁺, Tm³⁺ (NYF) microsphere loaded graphitic C₃N₄ (g-C₃N₄) nanosheets (Au-NYF/g-C₃N₄) was subtly designed and synthesized. The simple one-step synthesis of NYF in the presence of g-C₃N₄, which has not been reported in the literature either, leads to both high NYF yield and high coupling efficiency between NYF and g-C₃N₄. The Au-NYF/g-C₃N₄ structure exhibits high stability, wide photoresponse from the ultraviolet (UV), to visible and near-infrared regions, and prominently enhanced photocatalytic activities compared with the plain g-C₃N₄ sample in the degradation of methyl orange (MO). In particular, with the optimization of Au loading, the rate constant normalized with the catalysts mass of the best-performing catalyst 1 wt % Au-NYF/g-C₃N₄ (0.032 h^–1 mg^–1) far surpasses that of NYF/g-C₃N₄ and g-C₃N₄ (0.009 h^–1 mg^–1) by 3.6 times under λ > 420 nm light irradiation. The high performance of the Au-NYF/g-C₃N₄ nanocomposite under different light irradiations was ascribed to the distinctively promoted charge separation and suppressed recombination, and the efficient transfer of charge carriers and energy among these components. The promoted charge separation and transfer were further confirmed by photoelectrochemical measurements. The 1 wt % Au-NYF/g-C₃N₄ exhibits enhanced photocurrent density (∼6.36 μA cm^–2) by a factor of ∼5.5 with respect to that of NYF/g-C₃N₄ sample (∼1.15 μA cm^–2). Different mechanisms of the photodegradation under separate UV, visible, and NIR illuminations are unveiled and discussed in detail. Under simulated solar light illumination, the involved reactive species were identified by performing trapping experiments. This work highlights the great potential of developing highly efficient g-C₃N₄-based broadband photocatalysts for full solar spectrum utilization by integrating plasmonic nanostructures and upconverting materials.

The development of hybrid devices for photo-driven water oxidation with dinuclear molecular ruthenium catalysts on solid supports aims both at high efficiencies of the catalyst and at high stability of the linking to the surface. We herein report a systematic study regarding the stability of catalysts anchored on an indium tin oxide (ITO) support via different acid functional groups at the ligand backbone: viz., a single carboxylate anchor, two carboxylate anchors, and a phosphonate anchor. The integrity of the hybrid electrodes ITO|mesoITO|catalyst was evaluated under acidic aqueous conditions as a function of the applied electric potential below and above the onset of the oxygen evolution reaction (OER). Rotating ring disk electrode (RRDE) experiments allowed us to distinguish between the water oxidation and the desorption processes. X-ray photoemission (XPS) and X-ray absorption spectroscopy (XAS) after electrochemical treatment showed high chemical stability of the catalyst core structure but pronounced dependence of the hybrid stability on the oxidation state of the ruthenium center. A combination of these different spectroscopic techniques shed light on the mechanisms underlying catalyst desorption. Specifically, catalysts equipped with carboxylate anchors are found to continuously desorb already at low applied potentials below the OER onset, while for the more rugged phosphonate-based hybrid oxidative P–C(aryl) bond cleavage is proposed to occur, but only after reaching the high-valent Ru^VRu^IV state. These findings reveal specific challenges for anchoring strategies in molecular water oxidation catalysis.

Recently, metal-free nitrogen-doped graphene quantum dots (NGQDs) have been experimentally demonstrated to electrochemically convert CO₂ into high-order hydrocarbons and oxygenates, after more than 30 years since the identification of copper as an active metal catalyst for such conversions. However, the physicochemical principle of such catalytic activity for NGQDs has remained unclear. Here, by performing first-principles simulations, we have systematically investigated the underlying mechanisms governing the whole process. The introduction of N atoms into edges of graphene quantum dots enhances their bonding with *COOH, effectively promoting the reduction of CO₂ to CO. By including the influences of water, we reveal that the selective production of CH₄ over CH₃OH is attributed to a much lower kinetic barrier for the conversion of adsorbed *CH₂OH to *CH₂ via water molecule mediated proton shuttling. Further, adsorbed *CH₂ provides active sites for the coupling with CO to generate C₂ products, including both C₂H₄ and C₂H₅OH. These results offer theoretical insights into the reduction pathways of CO₂ on NGQDs, which may facilitate the design of metal-free carbon-based catalysts for efficient CO₂ reduction.

A series of tetrabutylphosphonium ([Bu₄P]⁺)-based ionic liquids (ILs) with multiple-site for CO₂ capture and activation in their anions, which could efficiently catalyze the cyclization reaction of propargylic alcohols with CO₂ at ambient conditions, are reported. Especially, the IL, [Bu₄P]₃[2,4-OPym-5-Ac], which has three interaction sites for attracting CO₂ together with a pK_a1 value of 9.13, exhibited the best performance, affording a series of α-alkylidene cyclic carbonates in moderate to good yields. The mechanism exploration demonstrated that IL served as a bifunctional catalyst with anion simultaneously activating CO₂ via multiple-site cooperative interactions and the C≡C triple bond in propargylic alcohol via inductive effect, thus resulting in the production of α-alkylidene cyclic carbonates.

Various parameters in the catalytic hydroconversion of triglycerides (palm oil) were carefully investigated for maximizing the production of biojet fuel. The results showed that the deoxygenation of triglyceride via hydrotreatment should be carried out in a separate reactor prior to the hydrocracking step (i.e., two-step reaction process). Otherwise, the CO generated during deoxygenation can poison the metal components in the metal/acid bifunctional catalysts (Pt/zeolites), which can cause significant imbalance between the metal and acid functions in hydrocracking. This leads to fast catalyst deactivation via coke formation, heavy formation of aromatics, and overcracking of hydrocarbons, resulting in the reduction of final biojet fuel yield. In the two-step process, the second hydrocracking step mainly determines the final biojet fuel yield, and thus, a rational design of the hydrocracking catalysts that can suppress overcracking is essential. The diffusion characteristics of the multibranched hydrocarbon (e.g., 2,2,4-trimethylpentane) in the hydrocracking catalysts could be correlated with the yields of the jet fuel-range C8–C16 hydrocarbons and the iso/n-paraffin ratios. The result indicates that the facile diffusion of multibranched isomers out of catalysts before excessive cracking is important for the suppression of the formation of light hydrocarbons (≤C7). Consequently, Pt supported on nanocrystalline large-pore BEA zeolite showed the largest biojet fuel yield with the highest iso-paraffin content. Under the optimized conditions, 55 wt % of biojet fuel with respect to palm oil was achieved after final distillation, which satisfied all the required fuel specifications.

Terpenoids form the largest and stereochemically most diverse class of natural products, and there is considerable interest in producing these by biocatalysis with whole cells or purified enzymes, and by metabolic engineering. The monoterpenes are an important class of terpenes and are industrially important as flavors and fragrances. We report here structures for the recently discovered Streptomyces clavuligerus monoterpene synthases linalool synthase (bLinS) and 1,8-cineole synthase (bCinS), and we show that these are active biocatalysts for monoterpene production using biocatalysis and metabolic engineering platforms. In metabolically engineered monoterpene-producing E. coli strains, use of bLinS leads to 300-fold higher linalool production compared with the corresponding plant monoterpene synthase. With bCinS, 1,8-cineole is produced with 96% purity compared to 67% from plant species. Structures of bLinS and bCinS, and their complexes with fluorinated substrate analogues, show that these bacterial monoterpene synthases are similar to previously characterized sesquiterpene synthases. Molecular dynamics simulations suggest that these monoterpene synthases do not undergo large-scale conformational changes during the reaction cycle, making them attractive targets for structured-based protein engineering to expand the catalytic scope of these enzymes toward alternative monoterpene scaffolds. Comparison of the bLinS and bCinS structures indicates how their active sites steer reactive carbocation intermediates to the desired acyclic linalool (bLinS) or bicyclic 1,8-cineole (bCinS) products. The work reported here provides the analysis of structures for this important class of monoterpene synthase. This should now guide exploitation of the bacterial enzymes as gateway biocatalysts for the production of other monoterpenes and monoterpenoids.

Metal-catalyzed in situ functionalization of ammonium ylides has emerged as a mild and atom/step economy strategy for the construction of complex building blocks. Despite the success, these trapping reactions are limited to activated polar double bonds such as (α,β-unsaturated) carbonyl derivatives. Trapping of ammonium ylides with nonpolar double bonds, which allows the all-carbon quaternary center, is unprecedented. In this article, an efficient stereoselective palladium-catalyzed intramolecular trapping of N-ylides derived from o-vinylaniline and α-diazocarbonyl compounds has been accomplished, a carbenylative hydroamination of alkenes. The present reaction allows the synthesis of various tri- and tetrasubstituted indolines in good yield with high diastereoselectivity. Important features are the construction of two contiguous quaternary carbon centers via the formation of C–N and C–C bonds in a single operation, high diastereoselectivity, wide functional group tolerance, and high atom and step economy. A reaction mechanism has also been explored by a combination of experimental and DFT studies, which revealed the formation of N-ylide followed by cyclization through metallo–ene-type reaction involving a six-membered cyclic transition state, where the diastereoselectivity is also established.

Reaction of N-R,N′-R′-2,5-diiminopyrroles (R = R′ = S-CH(Me)Ph; R = R′ = CH₂Ph; R = S-CH(Me)Ph, R′ = H) with Cu(OMe)₂ in the presence of chelating alcohols, ROH (R1 = C₂H₄NMe₂, R2 = C₂H₄Py, R3 = CH₂Py, R4 = CMe₂Py) yielded the dinuclear, alkoxide-bridged complexes L₂Cu₂(OR)₂. The complexes catalyze the polymerization of rac-lactide at room temperature with catalyst concentrations of 1–3 mM in 4–24 h (v = k[cat][monomer] with k = [2.3(5)] × 10² – [6.5(6)] × 10² M^–1 h^–1). EPR and mechanistic studies indicate that the complexes remain dinuclear during the polymerization reaction. In complexes with OR1, both alkoxides of the dimer initiate polymerization, with OR2 or OR3 only one alkoxide initiates polymerization, and OR4 is inactive in polymerization. The nature of the bridging ligand in the dinuclear complex determines stereocontrol. Independent of the spectator ligand L, complexes which retain an OR3 or OR4 bridging ligand in the active species show preference for isotactic polymerizations (P_m = 0.60–0.75), while those with only polymeryloxo bridges or OR2 as the bridging ligand provide atactic polymer. Stereocontrol follows a chain-end control mechanism, with the catalytic site likely adapting to the configuration of the chain end.