Spectroscopic study of a Cu/CeO2 catalyst subjected to redox treatments incarbon monoxide and oxygen

Redox processes induced by interaction of a calcined Cu/CeO2 catalyst with CO and reoxidation with Oz have been investigated by CO-TPR, EPR, FTIR of a dsorbed CO, and XPS. The initial calcined sample shows the presence of disp ersed Cu2+ species, which give rise in the EPR spectrum to signals due to i solated entities, a somewhat more aggregated Cu2+-containing phase, and cop per ionic pairs, in coexistence with an EPR-silent CuO-type phase, revealed by XPS. A significant reduction of copper is produced already by contact w ith CO at room temperature, EPR results suggesting that reducibility of Cu2 + species decreases with their aggregation degree. Simultaneously, the ceri a surface is also reduced by this interaction, copper acting as a strong pr omoter of this process. A singular consequence of the synergistic reduction of both components is observed by subjecting the catalyst to CO at T-r gre ater than or equal to 473 K, at which the CO adsorption capability of coppe r is apparently suppressed, in view of the absence of copper carbonyls in t he FTIR spectrum. This is attributed to the establishment of electronic int eractions between reduced ceria and small metallic copper particles generat ed by the reduction process. Contact of the GO-reduced sample with O-2 at r oom or higher temperature produces an important reoxidation of both copper and ceria, revealed by FTIR and EPR. The synergetic effects between copper and ceria in the reduction process and the easy reoxidation of deeply reduc ed ceria are thought to be crucial to explaining the high catalytic activit y shown by this system for CO oxidation. (C) 1999 Academic Press.