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Improving the selectivity in the oxidative coupling of methane to ethane/ethylene poses a significant challenge for commercialization. The required improvements are hampered by the uncertainties associated with the reaction mechanism due to its complexity. Herein, we report about 90 % selectivity to the target products at 11 % methane conversion over Gd2O3‐based catalysts at 700 °C using N2O as the oxidant. Sophisticated kinetic studies have suggested the nature of adsorbed oxygen species and their binding strength as key parameters for undesired methane oxidation to carbon oxides. These descriptors can be controlled by a metal oxide promoter for Gd2O3. [ABSTRACT FROM AUTHOR]

The present study of oxidative coupling of methane (OCM) over MnOx−Na2WO4/support catalysts demonstrated that the selectivity to C2H6 and C2H4 (C2‐hydrocarbons) is affected by the kind of support, co‐fed water, and the kind of oxidant (O2 vs. N2O). In addition to previous studies with MnOx−Na2WO4/SiO2, an enhancing water effect was obtained using catalysts based on TiO2‐ or ZrO2‐containing supports. However, a negative effect on methane conversion was established for SiO2−Al2O3‐supported catalysts. Temporal analysis of products with isotopic tracers suggests that the ability of MnOx−Na2WO4 to generate diatomic adsorbed oxygen species depends on the kind of support and is the key property for the water effect. The strength of the water effect on the activity decreases with an increase in the surface area of working catalysts. The kind of support also affects products selectivity due to its influence on the mobility/releasability of lattice oxygen in supported MnOx−Na2WO4. Among the prepared catalysts, MnOx−Na2WO4/TiO2 was found to be promising for H2O‐assisted OCM. The use of N2O instead of O2 further increases the selectivity to C2‐hydrocarbons to 84 % at 6.8 % CH4 conversion due to the formation of predominantly monoatomic oxygen species from N2O that selectively convert CH4 into C2H6. [ABSTRACT FROM AUTHOR]

Knowing the structure of catalytically active species/phases and providing methods for their purposeful generation are two prerequisites for the design of catalysts with desired performance. Herein, we introduce a simple method for precise preparation of supported/bulk catalysts. It utilizes the ability of metal oxides to dissolve and to simultaneously precipitate during their treatment in an aqueous ammonia solution. Applying this method for a conventional VOx−Al2O3 catalyst, the concentration of coordinatively unsaturated Al sites was tuned simply by changing the pH value of the solution. These sites affect the strength of V−O−Al bonds of isolated VOx species and thus the reducibility of the latter. This method is also applicable for controlling the reducibility of bulk catalysts as demonstrated for a CeO2−ZrO2−Al2O3 system. The application potential of the developed catalysts was confirmed in the oxidative dehydrogenation of ethylbenzene to styrene with CO2 and in the non‐oxidative propane dehydrogenation to propene. Our approach is extendable to the preparation of any metal oxide catalysts dissolvable in an ammonia solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alkali metal in MnO x -M 2 WO 4 /SiO 2 affects activity under anaerobic conditions. • Lattice oxygen of MnO x -M 2 WO 4 /SiO 2 can convert CH 4 to hydrocarbons. • OCM over MnO x -M 2 WO 4 /SiO 2 and M 2 WO 4 /SiO 2 proceeds via adsorbed oxygen species. • Presence of MnO x does not create more active sites but changes their reactivity. This work unveils the fundamentals relevant for activity and product selectivity in the oxidative coupling of methane (OCM) over the (MnO x)-M 2 WO 4 /SiO 2 (M = Na, K, Rb, or Cs) catalysts. The presence of the molten phase of Na 2 WO 4 and the ability of the catalysts to release lattice oxygen were not found to be the performance-governing factors. As proven by oxygen isotopic exchange experiments combined with thorough catalytic tests, the performance of both tri- and bimetallic catalysts is defined by the involvement of adsorbed oxygen species formed from gas-phase O 2. Lattice oxygen of M 2 WO 4 /SiO 2 is not capable of converting CH 4 to C 2 H 6 , while that of MnO x -M 2 WO 4 /SiO 2 is active for this reaction. The OCM activity of M 2 WO 4 /SiO 2 decreases with the atomic weight of alkali metal, whereas there is no such effect in the presence of MnO x , which, however, increases the activity. The enhancing effect was explained by improving the active site turnover. [ABSTRACT FROM AUTHOR]

Alkali metal promoters have been widely employed for preparation of heterogeneous catalysts used in many industrially important reactions. However, the fundamentals of their effects are usually difficult to access. Herein, we unravel mechanistic and kinetic aspects of the role of alkali metals in CO2 hydrogenation over Fe‐based catalysts through state‐of‐the‐art characterization techniques, spatially resolved steady‐state and transient kinetic analyses. The promoters affect electronic properties of iron in iron carbides. These carbide characteristics determine catalyst ability to activate H2, CO and CO2. The Allen scale electronegativity of alkali metal promoter was successfully correlated with the rates of CO2 hydrogenation to higher hydrocarbons and CH4 as well as with the rate constants of individual steps of CO or CO2 activation. The derived knowledge can be valuable for designing and preparing catalysts applied in other reactions where such promoters are also used. [ABSTRACT FROM AUTHOR]

The production of nitrous oxide, N2O, via NH3 oxidation is not on a practical scale due to the lack of a suitable catalyst. Instead, it is produced via thermal decomposition of NH4NO3, rendering N2O too costly and limiting its prospective uses. Herein, we report CeO2‐supported Au nanoparticles (2–3 nm) as a highly selective catalyst for low‐temperature NH3 oxidation to N2O, exhibiting two orders of magnitude higher space–time yield than the state‐of‐the‐art Mn−Bi/α‐Al2O3 and remarkable stability over 70 h on stream. The reaction proceeds via a Mars–van Krevelen mechanism, with the density of interfacial Auδ+ species and the oxygen storage capacity of CeO2 identified as the key performance descriptors. The latter could be enhanced by cobalt doping, improving the catalytic activity and setting a new benchmark for N2O productivity. These findings establish NH3 oxidation as an efficient process for N2O manufacture and facilitate its broader utilization in selective oxidations. [ABSTRACT FROM AUTHOR]

The article titled "Elucidating the Role of Oxygen Species in Oxidative Coupling of Methane over Supported MnOx-Na2WO4-containing Catalysts" in the journal ChemCatChem explores the main products of the oxidative coupling of methane reaction over different catalysts. The researchers found that a low catalyst surface area and low reactivity of support lattice oxygen are beneficial for achieving high selectivity to C2H6 and C2H4. The TiO2 support meets these requirements, while Al2O3 and ZrO2 supports predominantly produce CO or CO2. The selectivity to desired products over TiO2-supported catalysts can be improved by replacing O2 with N2O and/or co-feeding H2O to reduce the concentration of adsorbed diatomic oxygen species. [Extracted from the article]

This paper demonstrates the potential of Eu2O3 and Gd2O3 as catalysts for non-oxidative propane dehydrogenation to propene. They reveal a higher activity than the state-of-the-art bare ZrO2-based catalysts due to the higher intrinsic activity of Gdcus or Eucus in comparison with that of Zrcus (cus = coordinatively unsaturated). [ABSTRACT FROM AUTHOR]

In the article titled "Control of the Reducibility of Metal Oxides for Efficient Activation of C-H Bonds in Hydrocarbons," the authors discuss the challenge of designing metal oxide catalysts. They propose a method of controlling the structural properties of supported/bulk metal oxides through post-treatment in an NH3⋅H2O solution. This treatment allows for the dissolution and simultaneous precipitation of individual catalyst components, resulting in the ability to tailor catalyst reducibility. The authors highlight the importance of catalyst reducibility in the activation of C-H bonds in hydrocarbons. [Extracted from the article]

Au/TiO2 and Au/SiO2 catalysts containing 2 wt % Au and different amounts of K or Cs were tested for alcohol synthesis from CO2, H2, and C2H4/C3H6. 1‐Propanol or 1‐butanol/isobutanol were obtained in the presence of C2H4 or C3H6. Higher yields of the corresponding alcohols were obtained over TiO2‐based catalysts in comparison with their SiO2‐based counterparts. This is caused by an enhanced ability of the TiO2‐based catalysts for CO2 activation, as concluded from in situ fourier‐transform infrared (FTIR) spectroscopy and temporal analysis of products (TAP) studies. The synthesized carbonate and formate species adsorbed on the support do not hamper CO2 conversion into CO and the hydroformylation reaction. The transformation of Auδ+ to active Au0 sites proceeds during an activation procedure. As reflected by CO adsorption and scanning transmission electron microscopy, the accessible Au0 sites are influenced by the amount of alkali dopants and the support. FTIR data and TAP tests reveal a very weak interaction of C2H4 with the catalyst, suggesting its quick reaction with CO and H2 after activation on Au0 sites to form propanol and propane. Au NPs and alkali dopants—an effective team: In situ FTIR spectroscopy and temporal analysis of products reveal the importance of the type of support and alkali‐metal dopant on the performance of Au NPs for CO2 adsorption and its conversion with H2 into C3 or C4 alcohols in the presence of C2H4 or C3H6. The active Au0 sites required for the activation of all feed components are generated by in situ reduction of Auδ+ during an activation process. [ABSTRACT FROM AUTHOR]

Non-oxidative dehydrogenation of propane to propene is an established large-scale process that, however, faces challenges, particularly in catalyst development; these are the toxicity of chromium compounds, high cost of platinum, and catalyst durability. Herein, we describe the design of unconventional catalysts based on bulk materials with a certain defect structure, for example, ZrO2 promoted with other metal oxides. Comprehensive characterization supports the hypothesis that coordinatively unsaturated Zr cations are the active sites for propane dehydrogenation. Their concentration can be adjusted by varying the kind of ZrO2 promoter and/or supporting tiny amounts of hydrogenation-active metal. Accordingly designed Cu(0.05 wt%)/ZrO2-La2O3 showed industrially relevant activity and durability over ca. 240 h on stream in a series of 60 dehydrogenation and oxidative regeneration cycles between 550 and 625°C. [ABSTRACT FROM AUTHOR]

Keywords: Ammonia Oxidation; Au/CeO2; Metal-Support Interface; Nitrous Oxide; Reaction Mechanisms EN Ammonia Oxidation Au/CeO2 Metal-Support Interface Nitrous Oxide Reaction Mechanisms 1 1 1 04/27/22 20220502 NES 220502 B Ein Spiel zweier Hälften b Die direkte Oxidation von Ammoniak eröffnet einen Weg zur kostengünstigen und effizienten Produktion von Stickstoffoxid, einem vielversprechenden Reagens für selektive Oxidationsreaktionen. Rücktitelbild: Ceria-Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation (Angew. Ammonia Oxidation, Au/CeO2, Metal-Support Interface, Nitrous Oxide, Reaction Mechanisms. [Extracted from the article]

Ammonia Oxidation, Au/CeO2, Metal-Support Interface, Nitrous Oxide, Reaction Mechanisms Keywords: Ammonia Oxidation; Au/CeO2; Metal-Support Interface; Nitrous Oxide; Reaction Mechanisms EN Ammonia Oxidation Au/CeO2 Metal-Support Interface Nitrous Oxide Reaction Mechanisms 1 1 1 04/27/22 20220502 NES 220502 B A game of two halves b Direct ammonia oxidation unlocks a pathway towards affordable and efficient production of nitrous oxide, a highly promising agent for selective oxidation reactions, but necessitates the development of suitable catalysts. Back Cover: Ceria-Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation (Angew. [Extracted from the article]

A temporal analysis of products (TAP) reactor was used to study relationships between the mechanism of direct N2O decomposition over metal-loaded zeolites and their resulting activity. Rh-ZSM-5 (prepared by incipient wetness) and Fe-ZSM-5 (prepared by liquid-ion exchange) were chosen as prototypic catalysts displaying low (<550 K) and high (>650 K) temperature activity, respectively. Transient studies at the same contact time revealed the higher activity of Rh-ZSM-5 below 623 K and significantly stronger N2O adsorption over Rh species than over Fe species in the zeolites. Several microkinetic models were applied for simultaneous fitting the transient responses of N2O, N2, and O2. Classical reaction schemes failed to describe the experimental data. The preferred models of N2O decomposition over Rh-ZSM-5 and Fe-ZSM-5 differ in the reaction pathways of O2 formation. For both catalysts, free active metal sites (*) and those occupied by monoatomic oxygen species (*-O) from N2O participate in the decomposition of gas-phase N2O. Gas-phase O2 is formed directly on N2O interaction with *-O over Rh-ZSM-5, whereas the latter reaction over Fe-ZSM-5 leads to a surface bi-atomic oxygen species (O-*-O), followed by its transformation to *-O2. The latter species desorbs as molecular oxygen. Comparison of ion-exchanged and steam-activated Fe-ZSM-5 [J. Phys. Chem. B 110 (2006) 22586] revealed that the reaction mechanism is independent of the iron constitution induced by the preparation and activation routes, despite important differences in catalytic activity. Our quantitative microkinetic analysis demonstrated that both the stronger reversible N2O adsorption and, most importantly, the faster desorption of O2 are distinctive mechanistic features of Rh-ZSM-5, likely indicating its high de-N2O activity. [Copyright &y& Elsevier]

A detailed experimental analysis of reaction pathways proceeding in CO 2 hydrogenation over Fe-based catalysts was performed. The catalytic activity was measured at different degrees of conversion and used to analyze the production/consumption rates of reagents and products along the catalyst bed. It was demonstrated that except for the reverse water gas shift reaction and the subsequent hydrogenation of CO via Fischer-Tropsch (FT) mechanism, additional routes of hydrocarbon formation from CO 2 exist in the CO 2 hydrogenation. One of them is the methanation reaction which takes place over all studied catalysts. Another one is a direct pathway of C 2+ hydrocarbon formation from CO 2 that plays a significant role at least for some catalysts. In this route, iron carbides may be responsible for hydrogenating CO 2 into C 2+ hydrocarbons. Based on these results, the concept of requiring iron oxides as an essential active component for catalyzing the RWGS reaction in CO 2 -FT should be reviewed. [Display omitted] • Reaction pathways of CO 2 hydrogenation to hydrocarbons over Fe-based catalysts were analyzed. • Certain iron carbides are able to directly hydrogenate CO 2 into C 2+ hydrocarbons. • Iron oxides may not be essential for catalyzing the reverse water gas shift reaction in CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co/ZrO 2 catalysts with single Co2+ are efficient for C 3 H 8 dehydrogenation to C 3 H 6. • 1Co/ZrO 2 performed durable over multiple dehydrogenation/regeneration cycles. • 1Co/ZrO 2 showed higher activity than a commercial analogue of K-CrO x /Al 2 O 3. • The high activity results from a synergy effect between Co2+ and Zr cus. • Recombination of surface H species is the rate-limiting step in C 3 H 6 formation. Due to the increased production of shale gas containing propane, the share of non-oxidative propane dehydrogenation (PDH) in the large-scale production of propene is expected to continue to grow. There are, however, some ecofriendly and cost shortcomings associated with the currently applied Cr- or Pt-containing catalysts. Against this background, we present here Co/ZrO 2 alternatives and reveal the fundamentals affecting their activity, which can be used for purposeful catalyst design. Co2+ species homogeneously distributed within the lattice of ZrO 2 significantly increase the activity of coordinatively unsaturated Zr4+ for the PDH reaction. The increase is caused by accelerating both the cleavage of CH bonds in propane and the recombination of surface H species, with the latter reaction being the rate-limiting step. The best-performing catalyst outperformed an analogue of commercial K-CrO x /Al 2 O 3 in terms of the rate of propene formation and demonstrated durable performance over a series of 10 PDH/regeneration cycles under industrially relevant conditions. It also outperformed most previously developed Co-containing catalysts in terms of propene productivity. The space–time yield of propene formation achieved at 57 % equilibrium propane conversion at 550 °C was 0.71 kg·h−1·kg cat -1. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metallic Co0 species in situ formed are suggested to be the main active sites for PDH. • CoO x but not Co0 is responsible for the formation of undesired products. • Transformation of CoO x to Co0 depends on the strength of CoO x -support interactions. • Co/Silicalite-1 showed the C 3 H 6 space time yield of 1.50 kg·h−1·kg cat −1 at 550 °C. Although Co-containing catalysts show attractive performance in the non-oxidative propane dehydrogenation to propylene (PDH), their tailored development is hindered by the ambiguity in the kind of active sites (Co0 or Co2+O x) responsible for selective and unselective pathways. Herein, we demonstrate that supported CoO x species expends its lattice oxygen through oxidation of C 3 H 8 to CO 2 /C 3 H 6 and are accordingly transformed into Co0 species. The latter are decisive for the selective dehydrogenation of propane to propylene with high activity. The ability of CoO x to in situ form Co0 is affected by metal-oxide-support interactions (MOSI). In addition to the kind of support, defective OH groups (OH nests) in ZSM-5-type zeolites seem to be relevant for the MOSI effect. In comparison with previous studies highlighting the importance of the size of CoO x species and their acidity for coke formation, we could not establish any direct correlation. Nevertheless, the presence of CoO x seems to be relevant for this undesired reaction because the formation of coke is hindered when CoO x species are transformed to Co0 species. Catalyst acidic sites are responsible for cracking reactions. Thus, the derived mechanistic insights reveal the nature of active sites both for selective and unselective pathways and provide fundamentals for catalyst development. From an industrial viewpoint, the developed Co/Silicalite-1 (Co/S-1) catalyst with the weakest MOSI and accordingly highest fraction of Co0 showed the space time yield of propylene formation of 1.50 kg·h−1·kg cat −1 at 67 % equilibrium propane conversion and propylene selectivity of 95.3 % and the Co-related TOF value of 0.145 s−1 at 550 °C. These both activity values exceed those of the state-of-the-art Co-containing catalysts. The productivity of Co/S-1 is comparable or even higher than that of industrially relevant Pt- or Cr-containing catalysts. [ABSTRACT FROM AUTHOR]

Gold-based catalysts have shown high catalytic activity for reverse water gas shift (RWGS) reactions at low temperatures. Despite extensive studies, the RWGS reaction on Au-based catalysts with very low Au content (< 0.1 wt%) has not yet been investigated. In this study, TiO 2 and ZrO 2 supported gold catalysts with such low gold loading have been synthesized and tested for RWGS. The catalysts were investigated by a series of in/ex-situ characterization techniques, including ICP-OES, XRD, BET, XPS, STEM, STEM-EELS, TAP, in-situ DRIFTS and in-situ EPR. At 250 oC, the Au/TiO 2 catalyst showed almost 10 times higher activity than Au/ZrO 2. In-situ DRIFTS results suggest that the formate mechanism is the predominant mechanism over Au/ZrO 2 , while over Au/TiO 2 the reaction proceeds via the formation of hydroxycarbonyl intermediates. A combined study including STEM, STEM-EELS, XPS, and in-situ EPR suggests that the interfacial Au–O v –Ti3+ sites are responsible for the superior activity of Au/TiO 2. [Display omitted] • Au/TiO 2 exhibited superior activity and CO selectivity. • Ti3+formation and oxygen vacancies on Au/TiO 2 contribute to its superior activity. • The weak adsorption strength of CO is responsible for the superior CO selectivity. • An Oxygen-vacancies-engaged reaction mechanism is proposed for RWGS over Au/ZrO 2. • The decomposition of formate seems to be the rate-limiting step in the CO formation. [ABSTRACT FROM AUTHOR]