Selective oxidation of ammonia over copper-silver-based catalysts

A novel catalyst based on copper-silver was developed to solve the contradiction between the high conversion temperature of Cu-based catalyst and low N2 selectivity of Ag-based catalyst during selective oxidation of ammonium gas. The Cu-Ag-based catalyst (Cu 5 wt.%-Ag 5 wt.%/Al2O3) displayed a relatively low complete conversion temperature (<320 °C) with a high N2 selectivity (>95%). Increasing loading of Cu and Ag decreases N2 selectivity. The low N2 selectivity of Ag-based catalyst is possibly related to the formation of Ag2O crystals. Improvement of N2 selectivity of Ag-based catalyst was obtained by doping Cu to decrease crystallized Ag2O phase. The temperature programmed reaction (TPR) data show that N2O is the main byproduct of oxidation of ammonia at temperature lower than 200 °C. Two bands of nitrate species at 1541 and 1302 cm−1 were observed on Ag 10 wt.%/Al2O3 at the temperature higher than 250 °C, which indicates the formation of NOx during the selective catalytic oxidation of ammonia. No nitrate species was observed on Cu 10 wt.%/Al2O3 and Cu 5 wt.%-Ag 5 wt.%/Al2O3, while only one nitrate species (1543 cm−1) existed on Cu 10 wt.%-Ag 10 wt.%/Al2O3. We proposed that mixing Ag with Cu inhibited the formation of NOx during the selective catalytic oxidation of ammonia over Cu-Ag/Al2O3.