Surface-dependent CO oxidation over Au/ZnO nanopyramids and nanorods

Abstract

The catalytic activity of metals is very sensitive to the surface orientation of supporting oxides but rather little is known about ZnO in this regard. Nanostructured support morphologies present an attractive research strategy there because they allow probing the catalytic impact of well-defined surfaces at ambient pressure. The predominant {101̅0} side planes of hexagonal ZnO nanorods (NR) are terminated with the same number of O and Zn atoms while both the (0001) basal and {101̅1̅} side planes of hexagonal ZnO nanopyramids (NPy) are Zn-terminated. STEM analyses reveal two Au//ZnO interfacial configurations for each system after deposition of ∼3 nm Au nanoparticles. CO oxidation proceeds 15 times faster over the Au/ZnO NR than the Au/ZnO NPy catalyst at room temperature. The difference in catalytic activity can be traced to facilitated CO activation at the interfacial sites of Au/ZnO NR while it is retarded due to co-adsorption of CO with CO32- at undercoordinated Zn2+ ions of the interfacial perimeter of Au/ZnO NPy according to CO DRIFTS analyses. These results demonstrate that the catalytic behavior of metal/ZnO systems are very sensitive to ZnO surface terminations and the associated metal//ZnO interface configurations.