A combined theoretical and experimental investigation on the photocatalytic hydrogenation of CO on Cu/ZnO polar surface.

The photocatalytic hydrogenation of CO by Cu-deposited ZnO (Cu/ZnO) polar surfaces is investigated through density functional theory (DFT) calculations combined with experimental work. The DFT results demonstrate that, without Cu-loading, CO and H present weak physisorption on the clean ZnO polar surface, except that H undergoes strong chemisorption on the ZnO(0001̄) surface. Cu deposition on the ZnO polar surface could remarkably enhance the CO chemisorption ability, due to the induced charge redistribution on the interface of the Cu/ZnO polar surface systems. Additionally, a Cu-nanoisland, which was simulated using a Cu(111) slab model, exhibited strong ability to chemically adsorb H. Thus, H may act as an adsorption competitor to CO on the Cu/ZnO(0001̄), while, in contrast, CO and H (syngas) may have more opportunity to simultaneously adsorb on Cu/ZnO(0001) to promote the CO hydrogenation. These facet-dependent properties lead us to assume that Cu/ZnO(0001) should be a favorable photocatalyst for CO hydrogenation. This assumption is further verified by our photocatalysis experiment based on a ZnO single crystal. According to the theoretical and experimental results, the optimal HCOO* reaction pathway for the photocatalytic hydrogenation of CO on Cu/ZnO(0001) is proposed. In this optimal HCOO* path, the hydrogenation of CO* step and hydrogenation of HCOO* step could be promoted by the coupling of a photo-generated spillover proton and a photoelectron on the interface of Cu/ZnO(0001). This research demonstrates the feasibility of the photocatalytic reduction of CO on Cu/ZnO(0001), and will help to develop related high-efficiency catalysts.