Understanding the Synergistic Catalysis in Hydrogenation of Carbonyl Groups on Cu-Based Catalysts

Abstract

Understanding the synergy of Cu0 and Cu+ in hydrogenation reactions is indispensable for reasonably modulating the product distributions and improving the catalyst design. Herein, we investigated the hydrogenation of dimethyl oxalate on CeZrOx-supported Cu with varying molar ratios of nCu+/nCu0. A volcano-type correlation of structure and activity indicates that the selectivity of ethylene glycol is strongly dependent on the nCu+/nCu0 ratio, arising from the matching of rates for the activation of carbonyl group-included reactants and H2 on Cu+ and Cu0, respectively. The maximal selectivity toward ethylene glycol is achieved at a ratio of 0.15; deviating from this value leads to the favorable formation of methyl glycolate, a primary product. Results obtained from temperature-programmed surface reactions indicate that the presence of Cu+ and oxygen vacancies (OV) reduces the reaction temperature for the hydrogenation of carbonyl groups. Theoretical data show that the OV located at the copper–ceria interface induces a downward-directed adsorption configuration of the reaction intermediate adsorbed at the Cu+ site, compared to the presence of an upward-directed counterpart at the Cu0–Cu+ center. This change leads to a reduction in the kinetic barrier for the subsequent hydrogenation step, which consumes active *H species transferred from adjacent Cu0 via a hydrogen spillover process. Manipulating the Cu valence state and oxygen vacancies via interfacial engineering offers a viable strategy for governing product distributions, serving as an inspiration for the design of selective hydrogenation catalysts.