Roles of chemisorbed oxygen and zinc oxide islands on copper(110) surfaces for methanol decomposition

Abstract

The interaction of methanol with Cu-Zn-O surfaces is studied on a model system produced by depositing zinc oxide islands on Cu(110) surfaces. Various amounts of oxygen are then adsorbed onto the exposed copper part of the surface to form ZnO{sub x}/y ML O/Cu(110) surfaces. The role of O/Cu(110) in methanol decomposition on the authors model Cu-Zn-O surfaces was discerned by examining the interaction of methanol, adsorbed at 150 K in ultrahigh vacuum, with these ZnO{sub x}/y ML O/Cu(110) surfaces using temperature-programmed desorption (TPD), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES). Methanol reduces the zinc oxide and removes oxygen chemisorbed on copper. The decomposition temperatures of formate and methoxy species formed upon methanol decomposition on the components of oxygen covered Cu(110) and ZnO{sub x} are unaffected by the presence of the other component. However, the amount of formate species decomposed on the ZnO{sub x} component of ZnO{sub x}/O/Cu(110) surfaces is controlled by the amount of chemisorbed oxygen on copper. The authors show that there are cooperative effects between O/Cu and ZnO which increases the total amount of formate formed; for ZnO{sub x}/0.2 ML O/Cu(110) surfaces, the concentration of surface formate doubles on the three-component system as compared tomore » the sum of the concentration of formate species on the separate components. This produces a change in the relative surface formate to methoxy ratio from 1:9, for the case of 0.2 ML O/Cu(110), to 1:3, for the case of ZnO{sub x}/0.2 ML O/Cu(110) surfaces. 20 refs., 12 figs., 3 tabs.« less