EXAFS and XPS investigations of Cu/ZnO catalysts and their interaction with CO and methanol

Abstract

Several investigations have been carried out on Cu/ZnO catalysts by employing extended X-ray absorption. ne structure (EXAFS) and X-ray photoelectron spectroscopy (XPS). EXAFS investigations of Cu/ZnO catalysts subjected to hydrogen reduction show the presence of Cu1+ species and Cu microclusters. The proportion of Cu1+ depends on the rate of increase of the reduction temperature and on the amount of alumina added. An XPS study of the interaction of CO with model Cu/ZnO catalysts prepared in situ in the electron spectrometer shows the formation of CO2-, CO32- and C2O42- species, their proportion relative to CO increasing with the Cu1+ Cu-0 ratio. A study of the interaction of CH3OH with Cu clusters deposited on ZnO films reveals reversible molecular adsorption and the formation of CH3O on clean Cu clusters. If the Cu clusters are pretreated with oxygen, however, both CH3O and HCOO- species are produced. Model Cu/ZnO catalyst surfaces containing both Cu1+ and Cu-0 species show interesting oxidation properties. On a Cu-0-rich catalyst surface, only the CH3O species is formed on interaction with CH3OH. On a Cu1+-rich surface, the HCOO- ion is the predominant species.