Chloride-induced modifications of the properties of rhodia/ceria catalysts

A RhOx/CeO2 catalyst, prepared using RhCl3, is studied by EPR and IR spectr oscopies, comparing the results with those obtained for Cl-free RhOx/CeO2. The substitution of basic hydroxyls by chlorides produces an extensive modi fication of the ceria surface, describable as formation of a cerium oxychlo ride surface layer, which improves the dispersion of rhodia. The more coval ent character of Ce4+-O-2(-) bonds formed on the surface, the absence of ce ria-rhodia electron transfer and the stability of the surface against reoxi dation are interpreted in terms of a Cl-induced lowering of the cerium elec tron energy levels.