Selective catalytic oxidation of ammonia over AMn2O5 (A = Sm,Y,Gd) and reaction selectivity promotion through Nb decoration

Abstract Ammonia selective catalytic oxidation (NH3-SCO) represents an efficient technique to control the slip NH3, which has recently been found to be a significant factor in the formation of haze. It is highly desirable to have an NH3 -SCO catalyst with low cost, robust activity, high selectivity and wide operation temperature window at the same time. In this work, we have developed a series of precious-metal-free mullite based AMn 2O5 (A = Sm, Y, Gd) catalysts with better NH3-SCO performance than 1.2 %Pt/γ-Al2O3 samples, among which SmMn2O5 achieves the best low temperature activity with 97% of NH3 conversion at 180 °C. Combining in situ diffuse reflectance infrared Fourier transform spectroscopy analysis and density functional theory calculation, it was revealed that the rate determining step on SmMn2O5 was the formation of N2 from adsorbed –HNO and –NH groups. Based on this, the reaction selectivity of AMn2O5 was further improved by the surface Nb2O5 decoration. The promotional effect can be attributed to the enhanced catalyst’s attraction to the lone-pair electron of N atoms, which increases the –NH group amount and facilitates the reaction between –HNO and –NH groups to produce N2. Among all modified AMn2O5 catalysts, 5.0 %Nb2O5/SmMn2O5 stands out with a NH3 conversion of 96% and N2 selectivity of 68% at 180 °C, and a wide temperature window of 180 ~ 250 °C, that represents the best overall performance reported non-noble catalysts for NH3-SCO application.