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.