The Fabrication Of Supported Copper Catalyst And Its Property In The Selective Catalytic Oxidation Of Ammonia

Ammonia (NH3) is an inorganic odor-causing pollutant, and it not only endangers human health, but also threatens the ecological environment. With the increasing industrial ammonia waste stream, controling the NH3 pollution arouses great public concern. Selective catalytic oxidation of ammonia (SCO) is seen as an ideal technology to remove NH3 because of its high efficiency, cleanness and economic value.This paper focuses on the catalyst which is the core of SCO technology, and aims to prepare a kind of catalyst which has both high activity and N2 selectivity. The selective catalytic oxidations of ammonia were investigated over Cu/Al2O3, Cu/TiO2 catalysts with different Cu loadings and Cu-Mn/TiO2 catalyst, which were all prepared by an impregnation method, and the effects of NH3:O2 ratio and space velocity on SCO were also evaluated. The results showed that the selectivity to N2 was lower on Cu-Mn/TiO2 catalyst and 10% Cu/TiO2 catalyst has a much higher activity than Cu/Al2O3. When NH3:O2 ratio was 1:250 and space velocity was 50000h-1, the condition was optimum for Cu/TiO2 catalyst in the SCO of NH3.To further enhance the activity of copper-based catalyst, Cu/Ce-TiO2 catalysts under different conditions were prepared by a two-step method (added CeOx by the impregnation method and loaded Cu by homogeneous deposition precipitation) and their properties were tested in the selective catalytic oxidation of ammonia to nitrogen. The results showed that Cu/Ce-TiO2 (10 wt.%,9 wt.%,15 g L-1) catalyst exhibited the best performance for NH3 conversion and N2 selectivity, over which complete conversion of NH3 and the N2 selectivity of 95%were obtained at 250℃, moreover the temperature was only 190℃when 50% NH3 was converted, which descended 20℃compared to Cu/TiO2 catalyst.BET, XRD, XPS and H2-TPR have been used to characterize the states and reactivities of Cu/Ce-TiO2 catalysts for the oxidation of ammonia to nitrogen. The results indicated that the highly dispersed Cu2+species on the surface was more active than the large sized CuO particles in the bulk phase and Cu+species for the selective catalytic oxidation of ammonia. The concentration of urea greatly influenced the activity of Cu/Ce-TiO2 catalyst. When the concentration of urea was 15g L-1, part of Cu2O species changed into Cu(OH)2 species to form a Cu2+→Cu+reduction cycle, while Cu(OH)2 species could also react with NH3 and the reducibility of Cu2+species provided by Cu(OH)2 was higher. Therefore, the catalytic activity for selective catalytic oxidation of ammonia was improved. In addition, when appropriate amounts of Cu and Ce were loaded, Cu component was highly dispersed on the surface and the growth of bulk phase Cu component was inhibited. Due to the former was easier reduced, the catalytic activity increased accordingly.