X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY OF A CU-AL-O CATALYST UNDER H-2 OR CO ATMOSPHERES

The surface changes of a Cu-Al-O catalyst under H-2 or CO atmospheres have been followed by X-ray photoelectron spectroscopy (XPS). In both cases, the progressive reduction of copper(II) species in the octahedr al and tetrahedral sites to lower oxidation states for temperatures ab ove 250-degrees-C is observed. When the catalyst is reduced by H-2, th e main Cu 2p3/2 peak is resolved into its components (Cu2+, Cu+ in tet rahedral and octahedral sites, Cu0) and the proportion of the differen t copper species has been calculated. The concentration of Cu+ species in the octahedral environment is maximum after reducing the catalyst at 300-degrees-C, which corresponds to better catalytic activity in th e hydrogenation of dienes. In case of Cu-Al-O treated by CO where the catalyst surface contained copper species with oxidation states lower than +2, the adsorption of carbon monoxide in a molecular state seems more probable than dissociation which leads to carbidic species.