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A prerequisite for the development or optimization of heterogeneous catalysts is a comprehensive understanding of the reaction mechanism and kinetics at the level as elementary as possible. In comparison with steady‐state catalytic tests typically used for this purpose, non‐steady‐state (transient) studies provide deeper insights due to higher time resolution. For several decades, temporal analysis of products (TAP) and steady‐state isotopic transient kinetic analysis (SSITKA) have been successfully applied to the analysis of various heterogeneous reactions. In this review, we highlight the contributions made by TAP and SSITKA studies between 2017 and 2023 to the understanding of reaction mechanisms and to the derivation of microkinetics. The versatility of these methods is illustrated by the examples of oxidative coupling of methane, CO/CO2 hydrogenation to hydrocarbons or methanol, metathesis of ethylene with 2‐butenes to propene, acrolein oxidation to acrylic acid, methanol conversion to olefins and non‐oxidative propane dehydrogenation to propene. We also provide our personal views on possible developments in this area. [ABSTRACT FROM AUTHOR]

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]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Alkalimetallpromotoren werden in großem Umfang für die Herstellung heterogener Katalysatoren eingesetzt, die in vielen industriell wichtigen Reaktionen verwendet werden. Die Ursachen für ihre Wirkung sind jedoch in der Regel nur schwer zu ergründen. In dieser Arbeit werden die mechanistischen und kinetischen Aspekte der Wirkung von Alkalimetallen bei der CO2‐Hydrierung an Fe‐haltigen Katalysatoren mithilfe modernster Charakterisierungstechniken sowie räumlich aufgelöster stationärer und instationärer kinetischer Analysen aufgeklärt. Die Promotoren beeinflussen die elektronischen Eigenschaften von Eisen in Eisenkarbiden. Diese Karbideigenschaften bestimmen die Fähigkeit des Katalysators, H2, CO und CO2 zu aktivieren. Die Elektronegativität des Alkalimetallpromoters nach der Allen‐Skala wurde erfolgreich mit der Reaktionsgeschwindigkeit der CO2‐Hydrierung zu höheren Kohlenwasserstoffen und CH4 sowie mit den Geschwindigkeitskonstanten der einzelnen Schritte der CO‐ oder CO2‐Aktivierung korreliert. Die gewonnenen Erkenntnisse können für die Entwicklung und Herstellung von Katalysatoren für andere Reaktionen, bei welchen derartige Promotoren ebenfalls verwendet werden, von Nutzen sein. [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 Front Cover depicts the main products of the oxidative coupling of methane reaction over MnOx‐Na2WO4/support catalysts. In their Research Article, G. Jian, E. V. Kondratenko and co‐workers established that low catalyst surface area and low reactivity of support lattice oxygen are advantageous for achieving high selectivity to C2H6 and C2H4. The TiO2 support fulfills these requirements, whereas the use of Al2O3‐ or ZrO2‐containing supports leads to the predominant formation of CO or CO2. In addition, the selectivity to the desired products over TiO2‐supported catalysts can be improved by replacing O2 with N2O and/or through co‐fed H2O due to reducing the concentration of adsorbed diatomic oxygen species. More information can be found in the Research Article by G. Jian, E. V. Kondratenko and co‐workers. [ABSTRACT FROM AUTHOR]

The article titled "Back Cover: Controlling Metal-Oxide Reducibility for Efficient C-H Bond Activation in Hydrocarbons" discusses the challenge of designing metal oxide catalysts and proposes a method to control their structural properties. The authors, Bingsen Zhang, Evgenii V. Kondratenko, Zhong-Wen Liu, and others, suggest that catalyst post-treatment in an NH3⋅H2O solution can dissolve and precipitate individual catalyst components, allowing for the tailoring of catalyst reducibility. This is important for C-H bond activation in hydrocarbons. The article provides valuable insights for researchers interested in catalyst design and C-H bond activation. [Extracted from the article]

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]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

The simple deposition of tailored Rh or Pt nanoparticles (NP) on γ-Al2O3 results in active, selective, and stable catalysts for partial oxidation of methane (POM) to syngas. The NP were prepared by the ethylene glycol method in strong alkaline solution. This approach was found to be a promising way of providing active metallic NP for catalyzing the POM reaction. NP sizes determined by small angle X-ray scattering (SAXS) in solution and by transmission electron microscopy (TEM) on alumina were very close. This result highlights the possibility of easy pre-characterization of NP by the former method. Supported Rh NP are intrinsically more active in the POM reaction than Pt NP and also showed a superior performance compared with a conventionally prepared Rh catalyst, even if the latter had been pre-reduced. Mechanistic investigations in the temporal analysis of products (TAP) reactor indicate that the higher selectivity of well-defined Rh-NP is determined by their lower activity for consecutive CO transformations. [ABSTRACT FROM AUTHOR]