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A heterogeneous single‐atom catalyst (SAC) based on a tiny Cu loading (0.05 wt.%) supported on CeO2−TiO2 (Ce/Ti=0.18) shows very high Cu mass‐normalized CO oxidation activity, 100 % selectivity for CO2 between 60 and 100 °C and essentially no deactivation during 17 h on stream in the preferential oxidation of CO (PROX) at 120 °C. Based on state of the art, this catalyst is among the most active and PROX‐selective catalysts. Employing a combination of ex‐situ and operando methods, we infer that the isolated Cu single sites are incorporated with redox‐active Cu2+−O−Ce4+⇆Cu+−□−Ce3+ moieties connected by labile oxygen and are exposed on the surface of highly dispersed ceria. This high dispersion is promoted by TiO2 which itself does not participate in redox steps during PROX, as Ti ions remain essentially tetravalent while Cu and Ce undergo reversible redox shuttles. [ABSTRACT FROM AUTHOR]

A convenient and practical diastereoselective cis-hydrogenation of multi-substituted pyridines and arenes is reported. Applying a novel heterogeneous ruthenium catalyst, the corresponding piperidines and cyclohexanes are obtained in high yields (typically >80%) with a good functional group tolerance under mild conditions. The robust ruthenium supported catalyst is smoothly prepared and can be reused multiple times without activity loss. [ABSTRACT FROM AUTHOR]

For the first time, the oxidative dehydrogenation of (−)‐menthol to (−)‐menthone and (+)‐isomenthone in a marketable quality was carried out in a continuous gas phase reactor as a sustainable process using molecular oxygen as green oxidant and solid catalysts which do not contaminate the product mixture and which are easily to remove. The diastereomeric purity remained largely unchanged. Three types of catalysts were found to be very active and selective in the formation of menthone and isomenthone: AgSr/SiO2, CuO distributed on a basic support and RuMnCe/CeO2, where Ru, Mn and Ce exist in an oxidized state. The best overall yield of menthon/isomenthone obtained with an Ag‐based catalyst was 58 % at 64 % selectivity, with a Cu‐based catalyst 41 % at 51 % selectivity and with a Ru‐based catalyst 68 % at 73 % selectivity. Reaction conditions were widely optimized. [ABSTRACT FROM AUTHOR]

Abstract: A combined experimental and theoretical investigation of Ag‐Pt sub‐nanometer clusters as heterogeneous catalysts in the CO→CO2 reaction (COox) is presented. Ag9Pt2 and Ag9Pt3 clusters are size‐selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first‐principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano‐aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O2, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of Fe-based catalysts differing in surface Na/Fe ratio were prepared. • The critical role of Na is beyond its promotional effects under stationary operation. • Surface Na/Fe ratio determines the response of performance to fluctuating conditions. • Catalyst dynamics induced by fluctuating reaction conditions were studied. • The effect of Na in securing iron carbides was studied by in situ characterization. Considering the on-going developments of approaches for CO 2 capture, storage, and utilization, CO 2 hydrogenation with renewable H 2 can become sustainable technology to produce value-added chemicals/fuels in future feedstock scenarios. Herein, we investigate temporal behaviors of Fe-based catalysts in CO 2 hydrogenation under externally forced dynamics of reactor operation from the respective of composition and performance. Different catalyst preparation methods were applied to modulate the surface concentration of Na promoter but keeping the bulk concentration constant. The crucial promoter role in reserving catalyst performance and (un)steady-state catalyst composition during dynamic reactor operation was investigated by means of sophisticated catalytic tests combined with in situ and ex situ catalyst characterizations. The surface Na/Fe ratio of spent catalysts was identified as the decisive descriptor for production of the desired products under dynamic CO 2 hydrogenation conditions. The derived knowledge could be useful for redesigning catalysts and optimizing reaction processes when employing fluctuating energy supply. [ABSTRACT FROM AUTHOR]

The synthesis of primary alcohols (from olefins) is an important and challenging transformation, as most of the current methods suffer from regioselectivity issues. This work describes the utilization of rice husk (RH) from agricultural waste as support for the preparation of a catalyst for the conversion of olefin oxides to primary alcohols. The catalyst was synthesized by pyrolysis of RH impregnated with nickel, and characterized by IR, AAS, XRD, BET, XPS, TEM, and TPD technics. The catalyst shows excellent activity and selectivity towards anti‐Markovnikov alcohols, acting simultaneously as Brønsted acid, solid Lewis acid, and as hydrogenation catalyst. A substrate screening was done, the catalyst's recycling stability was assessed, and a plausibly reaction mechanism was proposed. [ABSTRACT FROM AUTHOR]

Highlights from the article: Cover Feature: Heterogeneously Catalysed Oxidative Dehydrogenation of Menthol in a Fixed-Bed Reactor in the Gas Phase (ChemistryOpen 8/2019) Keywords: oxidative dehydrogenation; gas-phase reactions; supported silver catalyst; supported copper catalyst; supported ruthenium catalyst Oxidative dehydrogenation, gas-phase reactions, supported silver catalyst, supported copper catalyst, supported ruthenium catalyst.

Preferential CO Oxidation in H 2 -rich streams is a promising approach to decrease CO concentrations below 10 ppm for fuel cell applications. Herein, Cu catalysts supported on commercial CeO 2 are prepared by a simple ball-milling method with different Cu loadings (0.25, 0.5, and 1 wt%). The catalysts are characterized by various methods, including XRD, BET, STEM-EELS, and H 2 -TPR. The results show that the catalysts are highly active and selective during CO-PROX in 80 vol% H 2 -streams at different temperatures. Moreover, all catalysts exhibited high stability and 100 % CO 2 -selectivity throughout 75 h of reaction at 90 °C. However, increasing Cu loading caused a decrease in Cu-mass-normalized rate due to the formation of less active CuO x clusters. The combined results from operando DRIFTS, EPR and NAP-XPS reveal that single Cu atom sites on CeO 2 are the key factor for the enhanced catalytic performance while the decreased activity is due to CuO x cluster formation. • Supported Cu-single sites on commercial CeO 2 - are highly active and selective for CO-PRX reaction. • Cu/CeO 2 catalysts prepared by simple ball-milling method. • No appreciable deactivation during 75 h on stream with 100 % selectivity at 90 °C. • CuO x cluster/nanoparticles are less active for CO-PROX. • Cu2+−O–Ce4+ and Cu+−□−Ce3+ moieties are the active sites for CO-PROX. [ABSTRACT FROM AUTHOR]

A heterogeneous single‐atom catalyst (SAC) based on a tiny Cu loading (0.05 wt.%) supported on CeO2−TiO2 (Ce/Ti=0.18) shows very high Cu mass‐normalized CO oxidation activity, 100 % selectivity for CO2 between 60 and 100 °C and essentially no deactivation during 17 h on stream in the preferential oxidation of CO (PROX) at 120 °C. Based on state of the art, this catalyst is among the most active and PROX‐selective catalysts. Employing a combination of ex‐situ and operando methods, we infer that the isolated Cu single sites are incorporated with redox‐active Cu2+−O−Ce4+⇆Cu+−□−Ce3+ moieties connected by labile oxygen and are exposed on the surface of highly dispersed ceria. This high dispersion is promoted by TiO2 which itself does not participate in redox steps during PROX, as Ti ions remain essentially tetravalent while Cu and Ce undergo reversible redox shuttles. [ABSTRACT FROM AUTHOR]

CO 2 conversion to CO via the reverse water-gas shift (RWGS) reaction is a promising source of syngas for subsequent synthesis of liquid fuels and chemicals. Herein, we present the synthesis of catalysts containing Au supported on hydroxylated Na-modified ZrO 2 , with Au amounts ranging from 0.05 to 1 wt%. Systematic investigations reveal the formation of cooperative Au/Na sites at the interface. These sites cooperate synergistically to activate CO 2 and generate a high surface density of carboxylate-like species, which serve as highly active intermediates for CO formation. It was found that the RWGS reaction on the catalyst with low Au loading proceeds mainly via a carboxylate pathway, with bidentate formate acting as spectators. At higher Au loading, the bidentate formate pathway contributes somewhat to CO formation alongside the carboxylate pathway. Based on temporal analysis of products, we emphasize the significant roles of H 2 spillover and the metal-support interface in the RWGS reaction. [Display omitted] • ZrO2 prepared at high pH with NaOH contains strongly adsorbed surface Na species. • Hydroxylated Na-modified ZrO2 is an excellent support for gold catalysts for RWGS. • Surface Au and Na sites synergistically activate CO2 and boosting CO formation. • In-situ spectroscopic studies reveal carboxylate as active intermediates for RWGS. [ABSTRACT FROM AUTHOR]

Using cheap and non-toxic chelating agents during catalyst preparation is considered as an effective tool to control the particle size and to strengthen the metal-support interactions (MSI), while keeping the simplicity of the selected preparation method. The previous properties are useful to improve the catalyst activity, stability, and selectivity in dry reforming of methane (DRM). Therefore, we prepared a series of low Ni loading (2.5 wt%) catalysts supported over MgO-Al 2 O 3 (Mg/Al = 1.3) mixed oxide using the classic wet impregnation method modified with chelating agents (citric acid (CA), tartaric acid (TA) and diethylenetriaminepentaacetic acid (DTPA)) and subsequently evaluated these in DRM. Intensive catalyst characterization (ICP, BET, XRD, XPS, STEM, H 2 -TPR and O 2 -TPO) suggested the presence of different structure-activity relationships. Particularly, using chelating agents during catalyst preparation controlled the final particle size range, which in turn played a pivotal role in shaping the strength of the metal support interactions (MSI). These impacts were crucial to improve the activity, stability and to control the formation of coke deposits. Moreover, special focus was put on the catalytic testing of the outperforming sample (Ni(TA)/Mg 1.3 AlO x) prepared using tartaric acid as chelating agent under severe regimes prone to catalyst deactivation to demonstrate the benefits of the proposed preparation technique. [Display omitted] • Organic ligands affect Ni particle size and its metal-support interaction (MSI). • Adding tartaric acid (TA) during preparation gave the best catalyst. • Up to 60% less coking at high GHSV and excess CH 4. • Ni(TA)/Mg 1.3 AlO x lost only 10% conversion at 600 °C over 50 h runtime. • Ni reoxidation and coke deposition are the main reasons of catalyst deactivation. [ABSTRACT FROM AUTHOR]