X-ray photoelectron spectroscopic study of a Cu–Al–O catalyst under H2 or CO atmospheres

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 2p_3/2 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.