Improvement of NH3-SCR activity and resistance to SO2 and H2O by Ce modified La-Mn perovskite catalyst

Abstract

A series of Ce modified La-Mn perovskite catalysts are synthesized by sol-gel method and systematically characterized. The results showed that Ce doping can improve catalytic activity of La-Mn perovskite catalyst for NOx removal with NH3. When the Ce/Mn ratio is 0.2, the catalyst exhibits the best SCR activity and achieves 90% NOx conversion at 135 °C, above 70% N2 selectivity in the testing temperature, and 95% NOx conversion at 200 °C in the presence of SO2 and H2O. Ce modified La-Mn catalysts are porous and have perovskite structure of LaMnO3.15. However, the doped Ce ions do not completely enter the perovskite framework, while some of them form Ce oxides on the catalyst surface. Moreover, some of Mn ions do not participate into the formation of La-Mn perovskite structure but deposit on the catalyst surface with a form of Mn3O4 to maintain the perovskite structure stability and charge balance. The Ce doped La-Mn perovskite catalysts provide larger specific surface area, more acidic sites, more chemically adsorbed oxygen and better redox performance than the undoped sample, which is conducive to the de-NOx performance. SO2 is oxidized into SO3 and forms some sulfates, but Ce doping increases the tolerance of catalyst to SO2.