Oxygen vacancy regulation of microenviroment of Cu/ZnO catalyst for syngas conversion

Abstract

Syngas conversion into methanol or ethanol over Cu/ZnO catalyst has attracted great interest due to its low energy consumption and high value-added. Here, syngas conversion over perfect and defective Cu4/ZnO(0001) catalysts were investigated via combining density functional theory (DFT) and microkinetic simulations. Our calculations show a clear change in the reaction mechanism when going from perfect Cu4/ZnO(0001) surface to defective Cu4/ZnO(0001) with 5% oxygen vacancy (Ov) surface. The existence of Ov hinders the formation of methanol by increasing the activation barrier of CHO hydrogenation to CH2O, but promotes the coupling between CHO and CO and the formation of C-C-O precursors that are favorable to form ethanol. In essence, the surface localized microenviroment charge redistribution owing to the presence of Ov adjusts the product selectivity. Detailed Bader charge results for the first time quantitatively identify that Ov promotes the electron transfer between adsorbates and Cu4/ZnO(0001) surface, and then influences their electrostatic interaction and spatial structure, resulting in syngas conversion into different products. Microkinetic simulations show that the adsorption energies of CO and H on the Cu4/ZnO(0001)-5%Ov surface has a notable effect on product selectivity. In addition, we verify that the hydrogenation ability of Cu4/ZnO(0001) is not well with the presence or absence of Ov.