Rare earth oxide modified Cu-Mn compounds supported on TiO 2 catalysts for low temperature selective catalytic oxidation of ammonia and in lean oxygen

Abstract

Selective catalytic oxidation (SCO) of ammonia was carried out over Cu-Mn compounds catalysts modified with trivalent rare earth oxide Ce 2O 3 and La 2O 3 respectively. TiO 2 was used as support and different ratio of O 2 were tested in order to find an appropriate O 2 concentration (vol.%), and the results showed that 1%O 2 (vol.%) was propitious to SCO of ammonia. The effects of the two rare earth oxides modified catalysts Ce 2O 3-Cu-Mn/TiO 2 and La 2O 3-Cu-Mn/TiO 2 on the catalytic activity and selectivity of ammonia oxidation were investigated under the reaction condition of 500 ppm ammonia, 1%O 2 (vol.%), at the temperature from 125 to 250 °C. The results revealed the beneficial role of Ce 2O 3 and La 2O 3 in catalytic activity at low temperature and lean oxygen concentration, while the modification with Ce 2O 3 and La 2O 3 led to the negative influence on N 2 selectivity. For the catalysts modified with Ce showed lower NO and N 2O selectivity than the catalysts modified with La, then the effects of different Ce loadings on catalytic activity and selectivity were also considered, in combination with catalysts preparation methods, which include incipient wet impregnation, sol-gel method and co-precipitation. Results revealed that the catalysts prepared by sol-gel method obtained preferable catalytic activity compared with the others, reaching 99% ammonia at 200 °C, whereas 96% NO was detected. It also indicated that different catalyst preparation method significantly determined production distribution.