X-ray photoelectron spectroscopic study of a Cu–Al–O catalyst under H2or CO atmospheres

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Abstract
The surface changes of a Cu–Al–O catalyst under H2 or CO atmospheres have been followed by X-ray photoelectron spectroscopy (XPS). In both cases, the progressive reduction of copper(II) species in the octahedral and tetrahedral sites to lower oxidation states for temperatures above 250 °C is observed. When the catalyst is reduced by H2, the main Cu 2p3/2 peak is resolved into its components (Cu2+, Cu+ in tetrahedral and octahedral sites, Cu0) and the proportion of the different copper species has been calculated. The concentration of Cu+ species in the octahedral environment is maximum after reducing the catalyst at 300 °C, which corresponds to better catalytic activity in the 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.