NO reduction by CO on Ce-Fe mixed oxides and gold nanoparticles

Gold nanoparticles were synthesized by a colloidal method and deposited on a Ce0.8Fe0.2O2-delta mixed oxide. The resulting material was characterized by High-Resolution Scanning Transmission Electron Microscopy, Temperature-Programmed Reduction, Mossbauer Spectroscopy, Oxygen Storage Capacity, Adsorption and Temperature-Programmed Desorption (NO and CO) and DRIFT Spectroscopy in order to elucidate the influence of gold nanoparticles and oxygen vacancies of Ce0.8Fe0.2O2-delta support on the selective catalytic reduction of NO by CO. Ce0.8Fe0.2O2-delta support presented a higher NO conversion (95% at 250 degrees C; and 99% at 350 degrees C) than Au/Ce0.8Fe0.2O2-delta catalyst (48% at 250 degrees C). We propose that gold deposition changed the support surface sites by blocking oxygen vacancies, which are the dissociation centers of NO molecules, decreasing thereby the catalytic activity of the gold-based catalyst. On the other hand, gold nanoparticles improved the reducibility and the oxygen storage capacity of the mixed oxide because isolated Fe3+ (in OFeCe3 sites) become more reducible, which could be evidenced by the increased oxidation of CO to CO2 at room temperature. On Au/Ce0.8Fe0.2O2-delta, the oxygen needed for CO oxidation can be supplied by the mixed oxide crystalline lattice, possibly from interface sites between gold nanoparticles and the mixed oxide, once the oxygen from NO dissociation becomes less abundant.