Palladium interaction with CeO2, Sn-Ce-O and Ga-Ce-O layers

Using photoemission, we have studied the interaction of palladium with thin layers of stoichiometric ceria (Ce4+ character) and two mixed oxides, Ga-Ce-O and Sn-Ce-O, where cerium in the Ce3+ oxidation state is present. Palladium was found to partially reduce the CeO2 layer by introducing oxygen vacancies most probably in the vicinity of the growing Pd particles. In mixed oxide systems palladium very strongly interacts with both added metals-gallium and tin-leading to a breaking of metal-ceria bonds and the establishment of Pd-Ga(Sn) intermetallic compounds. As a consequence the ceria reoxidizes back to a Ce4+ oxidation state.