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

Abstract

Gold nanoparticles were synthesized by a colloidal method and deposited on a Ce0.8Fe0.2O2-δ mixed oxide. The resulting material was characterized by High-Resolution Scanning Transmission Electron Microscopy, Temperature-Programmed Reduction, Mössbauer 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-δ support on the selective catalytic reduction of NO by CO. Ce0.8Fe0.2O2-δ support presented a higher NO conversion (95% at 250 °C; and 99% at 350 °C) than Au/Ce0.8Fe0.2O2-δ catalyst (48% at 250 °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-δ, 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.