ZINC-OXIDE AND OXYGEN OVERLAYERS ON CU(110) - A MODEL FOR CU-ZN-O CATALYSTS

Submonolayers to multilayers of zinc and oxygen deposited in UHV on Cu(110) were characterized by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and temperature-programmed desorption (TPD) of CO, CO2, and zinc. It is shown that initially, ZnO(x) grows two-dimensionally on Cu(110), but heating above 300 K leads irreversibly to three-dimensional island formation. These three-dimensional ZnO(x) islands were then used with various amounts of chemisorbed oxygen on the exposed Cu(110) as models for Cu-Zn-O methanol synthesis catalysts. Methanol produces formates on the surface, the concentration of which can be controlled by the amount of chemisorbed oxygen. The oxygen coverage found on Cu-Zn-O methanol synthesis catalysts after reaction corresponds to the oxygen coverage at which maximum formate formation occurs on our ZnO(x)/O/Cu(110) surfaces.