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

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.