Insights into the crucial role of a Zn promoter for methanol dehydrogenation to methyl formate over Cu(111) catalysts.

Abstract

Zn-doped Cu(111) alloy (Cu3Zn(111)) and Cu(111) surfaces were built using density functional theory (DFT) calculations to investigate the role of the Zn promoter in the methyl formate (MF) synthesis by the direct dehydrogenation of methanol. The rate determining step (RDS) of the MF synthesis is the dehydrogenation of CH3O to CH2O on both the Cu3Zn(111) alloy and the Cu(111) surfaces. Nevertheless, the energy barrier of the RDS is 119.4 kJ mol-1 on the Cu3Zn(111) alloy surface, lower than that on the Cu(111) surface. Compared with the favorable CH3O-CH2O coupling on the Cu(111) surface, the CH3O-CHO coupling is kinetically favorable on the Cu3Zn(111) alloy surface. Moreover, the formation of the by-product CO is effectively suppressed over the Cu3Zn(111) alloy surface. In addition, the results of the d-band center show that the addition of the Zn promoter increases the electron density of copper atoms, which accounts for the reduction in the energy barrier for the CH2O formation and inhibition of the CO formation.