Why Nitrogen Oxide Inhibits CO Oxidation over Highly Dispersed Platinum Ceria Catalysts

The influence of nitrogen oxide on the lean CO oxidation activity of highly dispersed Pt/ceria and reference Pt/alumina catalysts has been studied by kinetic measurements and infrared spectroscopic characterization. Co-feeding of nitrogen oxide leads to the formation of nitrates on the supports that induce a highly oxidized character of the Pt sites and in the case of Pt/ceria, inhibit ceria lattice oxygens to react with CO adsorbed on Pt rim sites via a Mars-van Krevelen mechanism below the ignition temperature. The build-up of nitrates below the light-off temperatures is faster when CO is present in the feed. Above the light-off temperatures, carbonates replace the nitrates while the catalytic activity remains high.