Reduction of NO by H2 and CO on PdO-MoO3/?-Al2O3 of low molybdena loading

Abstract

The activity and selectivity in the catalytic reduction of NO by a mixture of CO and H2 of three PdO-MoO3/γ-Al2O3 catalysts are compared in the presence of varying amounts of oxygen at reaction temperatures from 100 to 550°C. The catalysts were prepared by different methods and contain about 2% Mo and 2% Pd. Results are compared with those for PdO/γ-Al2O3, PdO-MoO3/γ-Al2O3 containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. The PdO-MoO3/γ-Al2O3 catalysts are more active for the selective reduction of NO to N2 and N2O than PdO/γ-Al2O3 under slightly oxidizing conditions at temperatures from 300 to 550°C. At these reaction conditions, the fresh PdO-MoO3/γ-Al2O3 catalysts are comparable with a commercial Pt-Rh catalyst. The improved activity of PdO-MoO3/γ-Al2O3 relative to PdO/γ-Al2O3 is believed to be due to the interaction between Pd and Mo. The effect of O2 on the activity and selectivity of these catalysts is different in the reduction of NO by H2, by CO, and by a mixture of H2 and CO. The results using the mixture of reductants cannot be inferred from the results with the single reductants.