Model copper/zinc oxide catalysts for methanol synthesis: The role of surface structure

Clean polycrystalline copper foil, a Cu(110) single crystal, and Cu thin films deposited on zinc oxide single crystal were used to model copper-based catalysts for methanol synthesis and water gas shift reactions. Rate measurements from CO{dollar}sb2{dollar}/(CO)/H{dollar}sb2{dollar} mixtures over polycrystalline copper foil and Cu(110) single crystal model catalysts proved that both methanol synthesis and reverse water gas shift reactions are catalyzed by metallic copper. Both reactions were structure sensitive and were more active on Cu(110) than polycrystalline Cu (mainly Cu(111)).; Vapor deposited Cu on the Zn-terminated ZnO(0001) single crystal surface formed two-dimensional islands (i.e., islands that are only one atomic layer thick) at small coverages. These films showed metallic character after a coverage of 5% of monolayer. The two-dimensional Cu islands showed chemisorption properties similar to that of Cu(110) which is attributed to the fact that the Cu surface atoms in both are in a state of high coordinative unsaturation. The role of the ZnO support in Cu/ZnO catalysts is suggested on this basis to be associated with keeping Cu in this more active (110)-like form. The structure, electronic properties and chemisorption behavior of Cu islands on this Zn-terminated face of ZnO are compared to those of Cu on the O-terminated face.