We report on the activation of CO 2 on Ni single-atom catalysts. These catalysts were synthesized using a solid solution approach by controlled substitution of 1–10 atom % of Mg 2+ by Ni 2+ inside the MgO structure. The Ni atoms are preferentially located on the surface of the MgO and, as predicted by hybrid-functional calculations, favor low-coordinated sites. The isolated Ni atoms are active for CO 2 conversion through the reverse water–gas shift (rWGS) but are unable to conduct its further hydrogenation to CH 4 (or MeOH), for which Ni clusters are needed. The CO formation rates correlate linearly with the concentration of Ni on the surface evidenced by XPS and microcalorimetry. The calculations show that the substitution of Mg atoms by Ni atoms on the surface of the oxide structure reduces the strength of the CO 2 binding at low-coordinated sites and also promotes H 2 dissociation. Astonishingly, the single-atom catalysts stayed stable over 100 h on stream, after which no clusters or particle formation could be detected. Upon catalysis, a surface carbonate adsorbate-layer was formed, of which the decompositions appear to be directly linked to the aggregation of Ni. This study on atomically dispersed Ni species brings new fundamental understanding of Ni active sites for reactions involving CO 2 and clearly evidence the limits of single-atom catalysis for complex reactions.

The insertion of a nonactivated alkene into the MSi bond of a catalytically active transition‐metal complex has been demonstrated for the first time. Furthermore, the formation of CH4 instead of SiMe4 in the reaction of [(CO)4CoMe] with Me3SiH is clearly inconsistent with the traditional Chalk–Harrod mechanism for the transition‐metal‐catalyzed hydrosilation of olefins. Both reactions are key steps in a new proposal for the mechanism of this reaction.

The industrial low-temperature process has been applied for 50 years; however, in situ data under relevant conditions are rare. We report on the in situ quantification of the surface adsorbates present under industrially relevant conditions by high-pressure thermogravimetry. In addition, high-pressure IR spectroscopy is applied for the identification of carbon-based adsorbates. On a high-performance Cu/ZnO:Al catalyst it has been shown that during CO2 hydrogenation adsorbates of up to 1.9 wt % of the catalyst are reversibly accumulated, and 70% of the ad-layer consists of H2O-derived species. Under CO-hydrogenation conditions, the weight accumulation on the surface is limited to an increase of 1.2 wt % mainly due to the absence of H2O. The stable adsorbate layers from different feeds are qualitatively assigned by surface titration experiments and spectroscopic insights. In accordance with the literature, it is clearly illustrated that, on the basis of the feed-dependent coverage of the surface, different reaction mechanisms for the methanol formation are involved. These investigations under realistic conditions finally show the importance of Zn–OH groups, likely located at the Cu/ZnO interface, as being crucial for activation and hydrogenation of CO2-derived intermediates to CH3OH. The accumulation of H2O- and carbon-derived species on the surface of the catalyst might explain the poor activity in CH3OH formation at low temperatures and consequently limits the application of Cu/ZnO-based catalysts under mild, thermodynamically preferred conditions.

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The bulk crystal structure of an oxidation catalyst as the most popular descriptor in oxidation catalysis is not solely responsible for catalytic performance.