Identification of Synergistic Actions between Cu0 and Cu+ Sites in Hydrogenation of Dimethyl Oxalate from Microkinetic Analysis

The kinetics of dimethyl oxalate (DMO) hydrogenation over Cu(111) and Cu2O(111) has been studied to understand the role of Cu0 and Cu+ sites in ethyl glycol (EG) production over Cu-based catalysts by the combination of density functional theory calculations and microkinetic analysis. The calculated results suggest that the presence of the Cu+ sites would strengthen the binding of the reactants, products, and reaction intermediates to the substrate and thus promote the dissociation of DMO and H2. The Cu0 sites are found to be beneficial to the hydrogenation of the acyl species whereas the Cu+ sites are primarily responsible for the CH3OH formation. Microkinetic analysis indicates that the existence of the Cu+ sites would increase the turnover frequency for the EG formation on Cu(111) by a factor of 20, under typical operating conditions. Hence, the excellent catalytic performance of the Cu-based catalysts in the hydrogenation of DMO to EG is attributed to the synergistic effect between the Cu0 and Cu+ sites, and a proper Cu0/Cu+ molar ratio can dramatically improve the catalytic activity.