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International audience; Rhodium-catalysed hydroformylation, effective tool in bulk and fine-chemical synthesis, predominantly uses soluble metal complexes. For that reason, the metal leaching and the catalyst recycling are still the major drawbacks of this process. Single-atom catalysts have emerged as a powerful tool to combine the advantages of both homogeneous and heterogeneous catalysts. Since using an appropriate support material is key to create stable, finely dispersed, single-atom catalysts, here we show that Rh atoms anchored on graphitic carbon nitride are robust catalysts for the hydroformylation reaction of styrene.

This study shows the main pathways for the DRM reaction and the competitive RWGS reaction upon changing reaction conditions, displaying the importance of including lateral–lateral interactions to describe the reaction in agreement with the experiment.

A biphasic reaction approach is presented for the cycloaddition of CO2 to epoxides where the catalyst is dissolved in water droplets and the reaction occurs at the aqueous–organic interface allowing easy recycling of the catalyst by decantation.

The direct hydrogenation of CO or CO2 to methanol, a highly vivid research area in the context of sustainable development, is typically carried out with Cu-based catalysts. Specific elements (so-called promoters) improve the catalytic performance of these systems under a broad range of reaction conditions (from pure CO to pure CO2). Some of these promoters, such as Ga and Zn, can alloy with Cu and their role remains a matter of debate. In that context, we used periodic DFT calculations on slab models and ab initio thermodynamics to evaluate both metal alloying and surface formation by considering multiple surface facets, different promoter concentrations and spatial distributions as well as adsorption of several species (O*, H*, CO* and ) for different gas phase compositions. Both Ga and Zn form an fcc-alloy with Cu due to the stronger interaction of the promoters with Cu than with themselves. While the Cu-Ga-alloy is more stable than the Cu-Zn-alloy at low promoter concentrations (< 25%), further increasing the promoter concentration reverses this trend, due to the unfavoured Ga-Ga-interactions. Under CO2 hydrogenation conditions, a substantial amount of O* can adsorb onto the alloy surfaces, resulting in partial dealloying and oxidation of the promoters. Therefore, the CO2 hydrogenation conditions are actually rather oxidising for both Ga and Zn despite the large amount of H-2 present in the feedstock. Thus, the growth of a GaOx/ZnOx overlayer is thermodynamically preferred under reaction conditions, enhancing CO2 adsorption, and this effect is more pronounced for the Cu-Ga-system than for the Cu-Zn-system. In contrast, under CO hydrogenation conditions, fully reduced and alloyed surfaces partially covered with H* and CO* are expected, with mixed CO/CO2 hydrogenation conditions resulting in a mixture of reduced and oxidised states. This shows that the active atmosphere tunes the preferred state of the catalyst, influencing the catalytic activity and stability, indicating that the still widespread image of a static catalyst under reaction conditions is insufficient to understand the complex interplay of processes taking place on a catalyst surface under reaction conditions, and that dynamic effects must be considered. ISSN:2041-6520 ISSN:2041-6539

The direct hydrogenation of CO or CO

RuCl2(P–OP)(N–N) complexes (1) containing an atropisomerizable phosphine–phosphite (P–OP) and a chiral C2 symmetric diamine (N–N) are readily prepared as trans isomers by successive addition of P–OP and N–N ligands to RuCl2(PPh3)3. For these complexes, fast atropisomerization of the biaryl fragment at room temperature has been observed. Compound trans-1a cleanly isomerizes into a mixture of cis isomers in EtOH upon heating. DFT calculations reproduce accurately the ratio of isomers observed as well as the greater thermodynamic stability of the cis isomers of 1a. Complexes 1 are efficient catalyst precursors for the asymmetric hydrogenation of N-aryl imines 5 in toluene under very mild conditions using KOtBu as a base (4 bar H2, room temperature, 5/1/KOtBu = 500/1/10). Among the catalyst precursors, 1f provides good enantioselectivities in the hydrogenation of a wide range of N-aryl imines (84–96% ee, 16 examples). From DFT calculations, a mechanism consisting in stepwise transfer of a hydride and a proton from the dihydride to the imine has been proposed, with the most favourable paths for R and S products involving cis-dihydrides d1R and d3S, respectively. Among several hydrogen activation pathways examined in the pro-R route, the most favorable one consists of hydrogen coordination to a Ru–amido/amine adduct, followed by amine assisted activation of dihydrogen

Predicting the state of Cu under a broad range of reaction conditions (pressure and temperature with various adsorbates: CO2, CO, H2O, H*, and O*) is an important property to understand CO2 hydroge...

Metal-oxide interfaces are ubiquitous and non-innocent in heterogeneous catalysis. In the October issue of Chem, Chen and co-workers show how the electronic nature of oxygen in the metallic- and bimetallic-oxide interfaces drives the reaction of ethane and CO2 to either syngas (CO/H2) (dry reforming of ethane) or ethylene, CO, and H2O (oxidative dehydrogenation of ethane).

The two-dimensional morphology of molybdenum oxycarbide (2D-Mo2COx) nanosheets dispersed on silica is found vital for imparting high stability and catalytic activity in the dry reforming of methane. Here we report that owing to the maximized metal utilization, the specific activity of 2D-Mo2COx/SiO2 exceeds that of other Mo2C catalysts by ca. 3 orders of magnitude. 2D-Mo2COx is activated by CO2, yielding a surface oxygen coverage that is optimal for its catalytic performance and a Mo oxidation state of ca. +4. According to ab initio calculations, the DRM proceeds on Mo sites of the oxycarbide nanosheet with an oxygen coverage of 0.67 monolayer. Methane activation is the rate-limiting step, while the activation of CO2 and the C–O coupling to form CO are low energy steps. The deactivation of 2D-Mo2COx/SiO2 under DRM conditions can be avoided by tuning the contact time, thereby preventing unfavourable oxygen surface coverages. © 2020, The Author(s)., Nature Communications, 11 (1), ISSN:2041-1723

Cooperation between two different metals plays a crucial role in many synergistic catalytic reactions, such as the Sonogashira C-C cross-coupling reaction, where an interaction between the Pd and Cu centers is proposed in the transmetalation step. Although several heterobimetallic Pd/Cu complexes were proposed as structural models of the active species in Sonogashira coupling, the detailed understanding of the metal-metal cooperation in transmetalation is still lacking in current systems. In this work, we report a stepwise and systematic approach to building heteromultimetallic Pd/Cu assemblies as a tool to study metal-metal cooperativity. We obtained fully characterized Pd/Cu multimetallic assemblies that show reactivity in alkyne activation, formation of catalytically relevant aryl/acetylide species, and C-C elimination, serving as functional models for Sonogashira reaction intermediates. The combined experimental and DFT studies highlight the importance of ligand-controlled coordination geometry, metal-metal distances and dynamics of the multimetallic assembly for transmetalation step.

Heterogeneous catalysts in the form of atomically dispersed metals on a support provide the most efficient utilization of the active component, which is especially important for scarce and expensive late transition metals. These catalysts also enable unique opportunities to understand reaction pathways through detailed spectroscopic and computational studies. Here, we demonstrate that atomically dispersed iridium sites on indium tin oxide prepared via surface organometallic chemistry display exemplary catalytic activity in one of the most challenging electrochemical processes, the oxygen evolution reaction (OER). In situ X-ray absorption studies revealed the formation of Ir-V=O intermediate under OER conditions with an Ir-O distance of 1.83 angstrom. Modeling of the reaction mechanism indicates that Ir-V=O is likely a catalyst resting state, which is subsequently oxidized to Ir-VI enabling fast water nucleophilic attack and oxygen evolution. We anticipate that the applied strategy can be instrumental in preparing and studying a broad range of atomically dispersed transition metal catalysts on conductive oxides for (photo) electrochemical applications., ACS Central Science, 6 (7), ISSN:2374-7951

The direct hydrogenation of CO or CO2 to methanol, a highly vivid research area in the context of sustainable development, is typically carried out with Cu-based catalysts. Specific elements (so-called promoters) improve the catalytic performance of these systems under a broad range of reaction conditions (from pure CO to pure CO2). Some of these promoters, such as Ga and Zn, can alloy with Cu and their role remains a matter of debate. In that context, we used periodic DFT calculations on slab models and ab initio thermodynamics to evaluate both metal alloying and surface formation by considering multiple surface facets, different promoter concentrations and spatial distributions as well as adsorption of several species (O*, H*, CO* and ) for different gas phase compositions. Both Ga and Zn form an fcc-alloy with Cu due to the stronger interaction of the promoters with Cu than with themselves. While the Cu-Ga-alloy is more stable than the Cu-Zn-alloy at low promoter concentrations (< 25%), further increasing the promoter concentration reverses this trend, due to the unfavoured Ga-Ga-interactions. Under CO2 hydrogenation conditions, a substantial amount of O* can adsorb onto the alloy surfaces, resulting in partial dealloying and oxidation of the promoters. Therefore, the CO2 hydrogenation conditions are actually rather oxidising for both Ga and Zn despite the large amount of H-2 present in the feedstock. Thus, the growth of a GaOx/ZnOx overlayer is thermodynamically preferred under reaction conditions, enhancing CO2 adsorption, and this effect is more pronounced for the Cu-Ga-system than for the Cu-Zn-system. In contrast, under CO hydrogenation conditions, fully reduced and alloyed surfaces partially covered with H* and CO* are expected, with mixed CO/CO2 hydrogenation conditions resulting in a mixture of reduced and oxidised states. This shows that the active atmosphere tunes the preferred state of the catalyst, influencing the catalytic activity and stability, indicating that the still widespread image of a static catalyst under reaction conditions is insufficient to understand the complex interplay of processes taking place on a catalyst surface under reaction conditions, and that dynamic effects must be considered., Chemical Science, 13 (45), ISSN:2041-6520, ISSN:2041-6539

Metallic copper generally adopts an FCC structure. In this work, we detect highly unusual BCC-structured Cu nanoparticles as a transient intermediate during the H-2 reduction of a Cu-I precursor, [(Cu4OBu4)-Bu-t], grafted onto the surface of partially dehydroxylated silica. The Cu BCC structure, assigned by in situ Cu K-edge XANES and EXAFS, as well as in situ synchrotron PXRD, converts upon heating into the most commonly found FCC allotrope. DFT calculations show that the BCC-Cu phase is in fact predicted to be more stable for small particles, and that their stability increases at lower H-2 concentrations. Using this knowledge, we show that it is possible to synthesize BCC-structured Cu nanoparticles as a stable allotrope by reduction of the same grafted precursor either in 10% H-2 diluted in Ar or 100% H-2 at low temperature., Physical Chemistry Chemical Physics, 2022 (39), ISSN:1463-9084, ISSN:1463-9076