Mechanistic insight into the catalytically active phase of CO2 hydrogenation on Cu/ZnO catalyst

Abstract

The catalytical active phase and reaction mechanism of methanol synthesis by hydrogenation of carbon dioxide on the surface of Cu/ZnO/Al2O3 catalyst become controversial topics in recent years. In this work, density functional theory calculations are employed to explore the possible mechanisms of the CO2 hydrogenation on three possible active phases, namely Zn/Cu interface, ZnO/Cu interface and hydroxylated Zn/Cu surface (i.e., ZnOH/Cu), which may exist in Cu/ZnO/Al2O3 catalyst under realistic conditions. It is more favorable that CO2 activation takes place by the formate pathway rather than the Reverse Water-Gas Shift pathway. Furthermore, the surface hydroxyl group could significantly increase the activity of formate pathway by improving the hydrogenation steps of HCOO to HCOOH and H3CO to H3COH, which are usually deemed as the rate-determining steps. These results suggest that the ZnOH/Cu phase is not only the most stable but also the most active phase for CO2 activation among Zn/Cu, ZnO/Cu and ZnOH/Cu, which could provide more insight into the design of highly efficient catalyst by tuning the surface active phase under operative conditions.