Active Cu0–Cuσ+ Sites for the Hydrogenation of Carbon–Oxygen Bonds over Cu/CeO2 Catalysts

CeO2-supported copper species have been reported as an active catalyst for the hydrogenation of carbon–oxygen bonds (CO, CO2, furfural, esters, etc.). However, the identification of active sites remains challenging. Herein, we prepared a series of rod-shaped ceria-supported copper catalysts with different copper sizes (single-atom, 1.4 nm nanoclusters, 3.0 nm and 6.8 nm nanoparticles) and applied them for methyl acetate (MA) hydrogenation. The structure and chemical environment of copper species were detected, and the surface Cu0 and Cuσ+ species and defects (oxygen vacancy and M–[Ox]–Ce solid solution) were quantitatively measured. To identify the active sites for MA hydrogenation, we also prepared contrast samples with increased surface defects or with reduced Cu0–Cuσ+ species. It is demonstrated that the Cu0–Cuσ+ species rather than oxygen vacancies or M–[Ox]–Ce solid solution are the primary active sites for MA hydrogenation. From the results of in situ experiments and various chemisorption and density functional theory calculations, the Cu0–Cuσ+ interface located at the surface Cu deposits is evidenced to play the key role in enhancing the adsorption and activation of MA. The turnover frequency of Cu/CeO2 catalysts for MA hydrogenation is linearly increased with the increase of the Cu0–Cuσ+ interfacial perimeter. This insight into active sites for carbon–oxygen bond hydrogenation may provide guidance for high-performance catalyst design.