Oxidation of NO over Supported Cr-Ce Mixed Oxide Catalysts

Chromium-cerium mixed oxides supported on TiO2, mesoporous SiO2, and TiO2-SiO2 were prepared by the impregnation method for the catalytic oxidation of NO to NO2. Activities of Cr-Ce mixed oxides as well as the nature of supports, molar ratio of Cr and Ce, load of the Cr-Ce mixed oxides, and calcination temperatures were investigated. For the optimal Cr-Ce/TiO2 catalyst, the NO conversion reached the thermodynamic equilibrium limitation of 80.7% at a reaction temperature of 330 degrees C with a space velocity of 10,000 h(-1). The H2O in the feed gas greatly depressed the catalyst activity by forming nitrate species on the surface of the catalyst, but the catalytic activity recovered with the removal of H2O. Moreover, increased temperatures alleviated the negative impact of H2O. Water together with SO2 in the feed gas exerted irreversible effects on the catalyst because of the generation of sulfite and sulfates on the catalyst surface. A heat treatment at 350 degrees C for 6h only partially restored the activity of the poisoned catalyst.