Activity and Synergy Effects on a Cu/ZnO(0001) Surface Studied Using First-Principle Thermodynamics

Using first-principle thermodynamics, we have studied surface phase diagrams of Cu substitutional ZnO(0001) surfaces under industrial conditions. On the one hand, the Cu substituted on Zn sites can promote efficient formation of oxygen vacancies on the ZnO(0001) surface. It can improve the activity on the Cu/ZnO(0001) surface. On the other hand, metallic monolayers containing certain Cu and Zn atoms can be also formed, accompanied by the oxygen vacancies formation. We have further investigated CO2 adsorption and reduction on these metallic monolayers. These metallic monolayers prefer to have an intermediate binding strength with the CO2 molecule. The intermediate binding strength was expected to be optimized for subsequent CO2 reduction. We have performed further studies and demonstrated successfully the improved catalysis for the subsequent CO2 reduction on these metallic monolayers. The relevant mechanism can be interpreted with the second synergy effect. The d-band states of these metallic monolayers, supported on the ZnO(0001) surface, are tuned to shift upward, that is, more close to Fermi level. Therefore, these metallic monolayers indeed exhibit promoted catalysis, in comparison with reported metallic surfaces in the literature.