Promoting effect of polyoxometallic acid modification on the NH3-SCR performance of Mn-based catalysts

Abstract

The strong oxidation capabilities of Mn sites render Mn-based catalysts showing high activities of selective catalytic reduction (SCR) at temperatures < 250℃, but simultaneously lead to the generation of by-product N2O with strong greenhouse effect. The activity-N2-selectivity trade-off was a prevalent observation in the development of Mn-based SCR catalysts. Here, a polyoxometallic acid enhancement strategy was devised to simultaneously promote the N2 selectivity and low-temperature SCR (LT-SCR) activity of Mn-based metal oxide catalysts, where the introduction of uniformly dispersed phosphomolybdic acid (HPMo) tuned the oxidation capabilities and enhanced NH3 adsorption-storage capability of catalysts. The combination of transient reaction, in-situ DRIFTS analysis and DFT calculations revealed that the main origin of N2O on the Mn-based catalysts was the deep oxidation of NH3, which was inhibited by the interaction between HPMo and Mn sites. Additional NH3 molecules adsorbed by the abundant acid sites supplied by HPMo further facilitated the SCR reaction. This strategy could guide the design of high-activity and high-selectivity LT-SCR catalysts for industrial denitration.