Importance of Metal-oxide Interfaces for Low Temperature CO Oxidation over Supported Au and FeOx Promoted Pt Catalysts

Low-temperature CO oxidation mechanisms were investigated for size-selected Au nanoparticle catalyst and water-treated Pt/FeOx–Al2O3 catalyst. Both catalysts had high CO oxidation activity even below room temperature. Interestingly, CO oxidations over these catalysts involved important contributions from the metal–oxide interface. For the Au catalyst system, the effects of heat-treatment in air and H2/Ar were investigated on Au/titania-coated silica aerogel catalysts prepared through adsorption of size-selected thiol-capped Au nanoparticles (AuNPs). Change in the form of sulfuric compound lead to a step-wise change in catalytic activity without affecting activation energy, which was observed for both active (<D>Au = 2 nm) and inactive (<D>Au = 4.9 nm) catalysts. These observations strongly indicate that the Au-titania interfaces function as reaction sites in low temperature CO oxidation over a wide Au size range. For the Pt catalyst system, Pt/Fe-containing alumina catalysts treated with water could catalyze CO oxidation with a very low activation barrier (9.2 kJ/mol). Pt nanoparticles and iron oxides formed efficient contacts in the catalysts, probably because of the enhanced mobility of Pt species induced by water treatment. Active oxygen is probably generated at the Pt–FeOx boundary, synchronized with the Fe redox reaction.