Investigation of Mn doped perovskite La-Mn oxides for NH3-SCR activity and SO2/H2O resistance

Abstract

A series of Mn doped perovskite La-Mn oxides were prepared and characterized systematically·NH3-SCR activity and the resistance to SO2 and/or H2O were evaluated. The results showed that LM-1.4 catalyst displays excellent LT SCR activity and wide window (80% NOx conversion in 100–300 °C). In the presence of SO2 and H2O, LM-1.4 catalyst can also achieve about 95% NOx conversion and N2 selectivity in long-term testing and good SCR activity (above 80% NOx conversion in 145–300 °C) in the cycles. The Mn doped La-Mn oxides have SBET of 86 m2/g and Vtotal of 0.27 cm3/g, but some Mn oxides do not enter the perovskite framework and form Mn3O4 and MnO2. Mn substituted A-site La ions in perovskite La-Mn oxides changes some of Mn3+ at the B-site in LaMnO3 to Mn4+ and some at the A-site to Mn2+. Doping of Mn can change redox properties of perovskite La-Mn oxides, but after the resistance testing in the presence of SO2 and H2O, the decrease of Mn4+ content and active oxygen species on the catalyst surface can weaken the redox properties of La-Mn oxides. Mn doping increases significantly the adsorption amount of NH3, but the formation of sulfate increases the strong acidity of the catalyst. Mn doping can also accelerate the decomposition of ammonium sulfate, resulting in an improvement of SO2-resistance.