Dynamic Behavior of the Surface Structure of Cu/ZnO/SiO2 Catalysts

In order to grasp the dynamic behavior of the surface composition of Cu/ZnO-based catalysts, the surface atomic densities of 63 Cu and 68 ZnO were determined separately with static LEIS on 63 Cu/ 68 ZnO/SiO 2 catalysts. Our data show that the methanol synthesis activity and surface composition of 63 Cu/ 68 ZnO/SiO 2 depend strongly on the reduction temperature between 473 and 673 K. The catalyst surface is strongly enriched in ZnO under methanol synthesis conditions. The oxidation state of the Cu species in the outermost atomic layer of the Cu/ZnO/SiO 2 surface has been determined by performing LEIS in combination with adsorptive decomposition of N 2 O. The observed oxidation behavior of the Cu species differs clearly from pure metallic Cu. This oxidation behavior and the methanol synthesis activity of the reduced catalyst surface are explained in terms of the formation of Cu(I)/ZnO with oxygen vacancies and are shown to be clearly affected by the reducing agent (being 5% CO/5% CO 2 /90% H 2 or pure H 2 ).