Ag Size/Structure-Dependent Effect on Low-Temperature Selective Catalytic Oxidation of NH3 over Ag/MnO2

Selective catalytic oxidation of ammonia (NH3-SCO) into N2 and H2O is considered to be a promising technique to eliminate NH3 pollution. Various Ag/MnO2 catalysts were prepared and applied to low-temperature (especially <100 °C) NH3-SCO. The Ag/MnO2-X (X indicating the calcination temperature) catalyst had a variable Ag size and structure depending on the calcination temperature from 200 to 500 °C. The Ag/MnO2-400 catalyst showed 10% NH3 conversion at 35 °C, and the temperature was 90 °C for the complete removal of 50 ppm NH3. More importantly, the N2 selectivities of NH3-SCO over Ag/MnO2-400 at the temperatures ranging from 30 to 120 °C were higher than 96%. Turnover frequencies of NH3 oxidation, N2 selectivity, and byproducts depended on the Ag size/structure. Ag/MnO2-400 with Ag particles of 2.4 nm diameter had the highest density of Ag particles over rod-shaped MnO2 during the reaction, which would be favorable for the formation of adsorbed NO and NH2NO intermediates to form N2 and H2O.