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The catalytic partial oxidation of methane is achieved at low temperatures (90% at ∼35% methane conversion at approximately 6 turnovers. Under our catalytic methane oxidation reaction conditions, MeTFA is stable against overoxidation, which explains the likely high selectivity at conversions >15%. Using combined experimental studies and DFT calculations, a mechanism involving soluble and molecular Mn species in the catalytic cycle is proposed. The proposed reaction pathway involves initial activation of Mnᴵᴵ by dioxygen, cleavage of a methane C–H bond by a Mnᴵᴵᴵ hydroxo intermediate, rebound of the methyl radical to generate MeTFA, and finally regeneration of the starting MnII complex. Also, this process is shown to be applicable to the oxidation of ethane, favoring the mono-oxidized product ethyl trifluoroacetate (EtTFA) and reaching ∼46% conversion.

Perovskite oxyhydrides such as BaTiO2.5H0.5 have been found to be able to catalyze NH3 synthesis, but the mechanism and the role of the catalyst’s lattice hydrides in the catalytic reaction remain unknown. Here we employ first principles density functional theory to investigate the mechanism of ammonia synthesis and the role of lattice hydrides on a prototypical perovskite oxyhydride, BaTiO2.5H0.5. Two mechanistic hypotheses, the distal and alternating pathways, have been tested on the Ti2O2 termination of the BTOH (210) surface, previously determined to be the most stable surface termination at the reaction conditions considered. In the distal pathway, H atoms hydrogenate N2 to form the *N-NHx key intermediates, followed by N-N bond breaking. In the alternating pathway, H atoms hydrogenate N2 in an alternating fashion to form the *NHx-NHy intermediates, before N-N bond breaking and formation of co-adsorbed *NHx/*NHy on the surface. We find that the subsurface hydride vacancy formed after reaction of *N2 with the lattice hydride is key to the distal pathway, leading to surface nitride formation after breaking the *N-NH3 bond, while the neighboring surface Ti sites are key to bridging and stabilizing the *NNH intermediate in the alternating pathway. In both pathways, desorption of NH3 is the most uphill process in energy. Our results provide important insights into the role of hydrides and surface vacancies in hydrogenation reactions over BTOH that will be useful to guide future spectroscopic experiments such as operando IR and inelastic neutron scattering to verify the key intermediates.

Catalytic CO2 sorbents, materials that adsorb and pre-concentrate CO2 on the catalyst surface prior to subsequent conversion, are becoming important materials in CO2 capture and utilization.

Cerium oxide (ceria) plays an important and fascinating role in heterogeneous catalysis as illustrated by its versatile use as a catalyst, a catalyst support, or a promotor in various oxidation and reduction reactions. Central to these reactions is the rich defect chemistry, facile redox capability, and unusual acid-base properties of ceria. Understanding the unique redox and acid-base properties of ceria is essential to build the structure-catalysis relationship so that improved catalytic functions can be achieved for ceria-based materials. Among the characterization toolbox, spectroscopic approach indisputably stands out for its unparalleled power in offering chemical insights into the surface properties of ceria at atomic and molecular level. In this review, we summarize advances in revealing the redox and acid-base properties of ceria via a variety of spectroscopic methods including optical, X-ray, neutron, electronic and nuclear spectroscopy. Both direct spectroscopy characterization and its coupling with probe molecules are analyzed to illustrate how the nature, strength and density of different surface sites are influenced by the pretreatment, the morphology and size of ceria nanoparticles. Further directions in taking advantage of in situ/operando spectroscopy for better understanding the catalysis of ceria-based materials are proposed in the summary and outlook section.

Supported Pd single atom catalysts (SACs) have triggered great research interest in methane combustion yet with contradicting views on their activity and stability. Here, we show that the Pd SAs can take different electronic structure and atomic geometry on ceria support, resulting in different catalytic properties. By a simple thermal pretreatment to ceria prior to Pd deposition, a unique anchoring site is created. The Pd SA, taking this site, can be activated to Pdδ+ (0δ2) that has greatly enhanced activity for methane oxidation: T50 lowered by up to 130 oC and almost 10 times higher turnover frequency compared to the untreated catalyst. The enhanced activity of Pdδ+ site is related to its oxygen-deficient local structure and elongated interacting distance with ceria, leading to enhanced capability in delivering reactive oxygen species and decomposing reaction intermediates. This work provides insights into designing highly efficient Pd SACs for oxidation reactions.

Developing an earth-abundant catalyst that is sulfur-tolerant, active, and highly selective is of great interest for valorizing natural gas streams containing sour gas. A tin-modified alumina catal...

Using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations, we conclusively demonstrate that acetaldehyde (AcH) undergoes aldol condensation when flown over ceria octahedral nanoparticles, and the reaction is desorption-limited at ambient temperature. trans-Crotonaldehyde (CrH) is the predominant product whose coverage builds up on the catalyst with time on stream. The proposed mechanism on CeO2(111) proceeds via AcH enolization (i.e., α C–H bond scission), C–C coupling, and further enolization and dehydroxylation of the aldol adduct, 3-hydroxybutanal, to yield trans-CrH. The mechanism with its DFT-calculated parameters is consistent with reactivity at ambient temperature and with the kinetic behavior of the aldol condensation of AcH reported on other oxides. The slightly less stable cis-CrH can be produced by the same mechanism depending on how the enolate and AcH are positioned with respect to each other in C–C coupling. All vibrational modes in DRIFTS are identified with AcH or trans-CrH, except for a feature at 1620 cm–1 that is more intense relative to the other bands on the partially reduced ceria sample than on the oxidized sample. It is identified to be the C=C stretch mode of CH3CHOHCHCHO adsorbed on an oxygen vacancy. It constitutes a deep energy minimum, rendering oxygen vacancies an inactive site for CrH formation under given conditions.

Strong metal-support interaction (SMSI) construction is a pivotal strategy to afford thermally robust nanocatalysts in industrial catalysis, but thermally induced reactions (>300 °C) in specific gaseous atmospheres are generally required in traditional procedures. In this work, a photochemistry-driven methodology was demonstrated for SMSI construction under ambient conditions. Encapsulation of Pd nanoparticles with a TiOx overlayer, the presence of Ti3+ species, and suppression of CO adsorption were achieved upon UV irradiation. The key lies in the generation of separated photoinduced reductive electrons (e-) and oxidative holes (h+), which subsequently trigger the formation of Ti3+ species/oxygen vacancies (Ov) and then interfacial Pd-Ov-Ti3+ sites, affording a Pd/TiO2 SMSI with enhanced catalytic hydrogenation efficiency. The as-constructed SMSI layer was reversible, and the photodriven procedure could be extended to Pd/ZnO and Pt/TiO2.

The demand for decarbonizing the ammonia industry by using renewable energy has invoked increasing research interests into catalyst development for effective N2 reduction under mild conditions. Hydride-based materials are among some of the emerging catalysts for ammonia synthesis at ambient pressure and low temperatures (

Plasma-assisted catalysis is an emerging technology for the atmospheric pressure and low bulk gas temperature synthesis of ammonia from molecular nitrogen and hydrogen. Direct evidence for plasma-i...

Although the coordinates of the metal atoms can be accurately determined by X-ray crystallography, locations of hydrides in metal nanoclusters are challenging to determine. In principle, neutron crystallography can be employed to pinpoint the hydride positions, but it requires a large crystal and a neutron source, which prevents its routine use. Here, we present a deep-learning approach that can accelerate determination of hydride locations in single-crystal X-ray structure of metal nanoclusters of different sizes. We demonstrate the efficiency of our method in predicting the most probable hydride sites and their combinations to determine the total structure for two recently reported copper nanoclusters, [Cu25 H10 (SPhCl2 )18 ]3- and [Cu61 (St Bu)26 S6 Cl6 H14 ]+ whose hydride locations have not been determined by neutron diffraction. Our method can be generalized and applied to other metal systems, thereby eliminating a bottleneck in atomically precise metal hydride nanochemistry.

Oxidative dehydrogenation of propane to propylene can be achieved using conventional, oxygen-assisted dehydrogenation of propane (O2–ODHP) or via the use of soft oxidants, such as CO2, N2O, S-conta...

A bulk γ-Al2O3 catalyst shows high selectivity for propane dehydrogenation upon pretreatment and co-feeding with H2S. The reaction kinetics, deactivation rates, and active sites for propane dehydrogenation on this catalyst were characterized using fixed bed conversion studies, NH3-TPD, O2-TPO, XPS, and density functional theory (DFT). Specifically, we observe that the selectivity to propylene was 94% at ca. 16% propane conversion at 560 °C for a C3H8:H2:H2S ratio of 1.1:1:0.1 on γ-Al2O3. Our results indicate that H2S can irreversibly modify the active sites of γ-Al2O3, postulated to be defect sites on the 110 facet comprised of a tri-coordinated Al atom, such that the modified site was more active and selective towards propylene and less inhibited by co-fed H2S. Along with XPS and O2-TPO, the dehydrogenation-regeneration experiments suggest the formation of sulfurous coke and strong adsorption of reaction products result in a less active catalyst. This study shows the potential of alumina/metal-sulfide as an earth-abundant and relatively benign class of catalysts for alkane activation, especially in the context of sour natural gas upgrading.

The construction of heterogeneous frustrated Lewis pairs (FLPs) with performance comparable to or surpassing the homogeneous counterparts in H

Strong metal–support interactions (SMSIs) and catalyst deactivation have been heavily researched for decades by the catalysis community. The promotion of SMSIs in supported metal oxides is commonly...

Ethanol is an important C2 platform molecule for producing value-added chemicals and distillate hydrocarbon fuels (e.g., jet and diesel). Among these, catalytic upgrading of ethanol to butenes can ...

Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions were (quasi) in situ studied using temperature programmed surface reaction spectra, diffuse reflectance Fourier transform infrared spectroscopy, inelastic neutron scattering spectroscopy and electron paramagnetic resonance. CO undergoes disproportion reaction to produce gaseous CO2 and surface carbon adatoms, and adsorbs to form surface formate species. H2 adsorption forms dominant irreversibly-adsorbed surface hydroxyl groups and interstitial H species and very minor surface Zn-H species. Surface formate species and hydroxyl groups react to produce CO2 and H2, while surface carbon adatoms are hydrogenated by surface Zn-H species sequentially to produce CH(a), CH2(a), CH3(a) and eventually gaseous CH4. The ZnO nanoplates, exposing a higher fraction of Zn-ZnO(0001) and O-ZnO(000–1) polar facets, are more active than the ZnO powders to catalyze CO hydrogenation to CH4. These results provide fundamental understanding of the reaction mechanisms and structural effects of CO hydrogenation reaction catalyzed by ZnO-based catalysts.

Hydrogen is ubiquitous in catalysis. It is involved in many important reactions such as water splitting, N2 reduction, CO2 reduction, and alkane activation. In this Perspective, we focus on the hyd...

Successful synthesis of some perovskite oxyhydrides and their unique catalytic properties have recently attracted researchers’ attention. However, their surface structure remains unclear. Here we i...

The partial or complete blockage of active sites of metal nanoparticles (NPs) on supported-metal catalysts has been of interest for tuning the stability, selectivity, and rate of reactions. Here, w...

Summary Toward the preparation of industrial metal oxide catalysts, sacrificial organic templates, excessive solvents, complex impregnation, and drying steps are generally required. Here, we report a versatile rule for the simple synthesis of highly porous metal oxides with well-dispersed noble metal species. Porous metal oxides (Co3O4, FexOy, and Cr2O3) are obtained with some surface areas (e.g., Cr2O3: 224 m2·g−1) beyond the record value. Surprisingly, small noble metal nanoparticles (e.g., Pd: 3.1 and Pt: 3.2 nm) could be incorporated by this solid-state process simultaneously. Corresponding Rh-Co3O4, Pd-FexOy, and Pt-Cr2O3 exhibit excellent performance: CH4 combustion (T90 = ∼360°C and thermal stability: >100 h at 680°C), hydrogenation of nitrobenzene and derivatives (turnover number [TON] = 2.49 × 104, 300 mmol per run), and reversed water gas shift (RWGS) reaction (44% CO2 conversion with ∼98% CO selectivity and thermal stability: >100 h at 500°C), respectively. Therefore, current principle via a NaCl-based solid solution could provide a solid-state, fast, and efficient route for processing metal oxide catalysts.

It is highly desirable to convert bioethanol to value-added chemicals. As such, conversion of ethanol to propene (ETP) is attractive because propene is an important raw material for the production of plastics. In2O3 has shown promising catalytic performance for ETP conversion. However, the underlying mechanisms remain elusive. In this work, we use density functional theory (DFT) to investigate ETP reaction pathways on the In2O3 (110) surface. We find that the ETP reactions proceed through three major stages: ethanol to acetaldehyde, acetaldehyde to acetone, and acetone to propene. The ethanol-to-acetaldehyde step is kinetically facile. Comparing the two pathways from acetaldehyde to acetone, we show that the aldol reaction pathway via direct coupling of two acetaldehyde is more favorable than the acetate-ketonization pathway. The acetone-to-propene process is found to be the rate-limiting step of the overall reaction. This work provides a detailed mechanistic view of the ETP chemistry on In2O3(110) that paves the way for further exploration of effects such as surface termination, surface doping, and co-feeding of H2 and H2O on selectivity and catalyst stability.

Cerium oxide (ceria) has found a wide variety of applications in catalysis including as a catalyst, a modifier, or a support, largely thanks to its robust redox properties and versatile acid-base function. While it is often utilized for oxidation reactions, ceria has recently attracted intense research interest for its unusual ability to selectively hydrogenate alkynes to alkenes. The intriguing hydrogenation ability of ceria has sparked renewed research efforts to understand how pure ceria works as a hydrogenation catalyst. In this review, recent advances in both experimental and computational studies of ceria are summarized, focusing on the interaction of ceria with H2 and in hydrogenation reactions. Significant insights from various studies including in situ spectroscopy/microscopy and theoretic modeling of ceria in hydrogen-involved reactions are discussed, which shed light on the origin of the hydrogenation ability of ceria and the reaction mechanisms involved in ceria-catalyzed alkyne hydrogenation. Ways to further improve both the mechanistic understanding and catalytic performance of ceria-based materials for hydrogenation reactions are proposed at the end in the summary and outlook section.

Although hexagonal boron nitride (h-BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas-phase methyl radicals (CH3 . ) in the ODHP reaction over boron-based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV-PIMS), which uncovers the existence of gas-phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C-H activation of propane, while C2 and C1 products can be formed via both surface-mediated and gas-phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron-based catalysts.

Ceria has been used as a hydrogenation catalyst especially in selective alkyne hydrogenation, but the reaction mechanism regarding the role of different surface hydrogen species remains unclear. In...

Recently, there have been renewed interests in exploring new catalysts for ammonia synthesis under mild conditions. Electride-based catalysts are among the emerging ones. Ruthenium particles supported on an electride composed of a mixture of calcium and aluminum oxides (C12A7) have attracted great attention for ammonia synthesis due to their facile ability in activating N2 under ambient pressure. However, the exact nature of the reactive hydrogen species and the role of electride support still remain elusive for this catalytic system. In this work, we report for the first time that the surface-adsorbed hydrogen, rather than the hydride encaged in the C12A7 electride, plays a major role in ammonia synthesis over the Ru/C12A7 electride catalyst with the aid of in situ neutron scattering techniques. Combining in situ neutron diffraction, inelastic neutron spectroscopy, density functional theory (DFT) calculation, and temperature-programmed reactions, the results provide direct evidence for not only the presence of encaged hydrides during ammonia synthesis but also the strong thermal and chemical stability of the hydride species in the Ru/C12A7 electride. Steady state isotopic transient kinetic analysis (SSITKA) of ammonia synthesis showed that the coverage of reactive intermediates increased significantly when the Ru particles were promoted by the electride form (coverage up to 84%) of the C12A7 support rather than the oxide form (coverage up to 15%). Such a drastic change in the intermediate coverage on the Ru surface is attributed to the positive role of electride support where the H2 poisoning effect is absent during ammonia synthesis over Ru. The finding of this work has significant implications for understanding catalysis by electride-based materials for ammonia synthesis and hydrogenation reactions in general.

Strontium titanate (SrTiO3) is an extensively investigated perovskite for various applications due to its optical, electrical and chemical properties. To gain an in-depth understanding of the active sites involved in heterogeneous catalysis over the broadly used SrTiO3 (STO), we studied a model reaction, isopropanol conversion, on three differently shape-controlled nanocrystals: cube, truncated cube and dodecahedra. SEM, XRD and XPS confirmed the morphology, phase and composition of STO shapes. Low energy ion scattering (LEIS) revealed the occurrence of surface reconstruction over STO shapes during O2 pretreatment at different temperatures. Based on the catalytic activities, scanning transmission electron microscopy images and density functional theory calculations, the step sites on STO derived from surface reconstruction were proposed to be the active sites for isopropanol conversion. This was further confirmed by steady state isotopic kinetic analysis (SSITKA) which demonstrated similar intrinsic turnover frequencies (TOFs) for the differently reconstructed STO shapes. It is concluded that the crystal facets impose an indirect effect on the catalysis of STO via controlling the degrees of surface reconstruction: the less stable STO (1 1 0) facet (dodecahedra) leads to more step sites after reconstruction and hence higher overall reaction rate than the more stable (1 0 0) facet (cube). This work highlights the important interplay between the crystal facet and surface reconstruction in controlling the nature and density of active sties and thus catalysis over complex oxides.

ABO3 perovskites are increasingly being explored as catalysts, but it is unclear how they behave as supports for single atoms and how the subsequent single-atom catalysts can be employed for important reactions such as methane activation. Here we examine the stability of Pt single atoms (Pt1) on the commonly exposed (100) surfaces of SrBO3 perovskites (B = 3d transition metals) and their methane-adsorption properties by first principles density functional theory. We find that the stability and charge state of Pt1 on the SrBO3(100) surfaces are termination-sensitive. Due to polar compensation, Pt1 is negatively charged on the A termination but positively charged on the B termination. This charge state greatly impacts methane adsorption: negatively charged Pt1 on the A-termination chemisorbs methane (in some cases, dissociatively), but positively charged Pt1 on the B-termination adsorbs methane physically. Analysis of the density of states of the negatively charged Pt1 reveals that its sp states are key to methane chemisorption and C–H activation. Our work shows that polar compensation on the perovskite surfaces can be used to tune the charge state of a single atom for methane chemisorption and C–H activation.

Hydrogen adsorption on transition-metal oxides can lead to surface metallization, but it is unclear how this change of surface property impacts the subsequent surface chemistry and catalysis. Herein, we investigate from the first-principles density functional theory how hydrogen-induced metallization affects the adsorption of common intermediates during the conversion of oxygenates and alkanes (such as alkoxy and alkyl groups) on the SrTiO3(001) surface. We find that alkoxy adsorption is greatly enhanced by hydrogen-induced metallization and the strength increases with the hydrogen coverage. This is because hydrogen adsorption leads to electron donation to the Ti site, which then forms a bond with the alkoxy group. The enhancement is found to be nonlocal. The same chemistry is also responsible for the enhanced adsorption of alkyl groups on the Ti site, which renders a switch in the site preference from the O site on pristine SrTiO3(001) to the Ti site on hydrogen-functionalized SrTiO3(001). These insights...

Catalysts are inherently dynamic in nature, as they respond to the environment by changing their local and extended structures. Surface reconstruction is among such dynamic behaviors of catalysts a...

Titanium dioxide (TiO2) represents a promising candidate for hydrogen production via photocatalysis. However, its large bandgap and fast charge recombination limits its efficiency. To overcome this...

As petroleum-related products dominate the global fuel market, acid gas resistant materials are in demand. ZnO is one of the widely used materials as SO2 sorbent and catalyst/catalyst support. To u...

The present study investigates the effect of sodium and tungsten promoters on Mg6MnO8-based redox catalysts in a chemical looping oxidative dehydrogenation (CL-ODH) scheme. CL-ODH has the potential...