Zr Doped La-Mn Perovskite Oxides: Nh3‒Scr Activity, Resistance to So2/H2o and Deactivation Mechanism

Abstract

NOx emitted in flue gas is a main air pollutant and commonly removed by the selective catalytic reduction of NOx with NH3 technology (NH3‒SCR), but SO2 in flue gas is easy to cause catalyst deactivation. Zr doped La-Mn perovskite oxides were prepared by citric acid sol-gel method, systematically characterized and evaluated for their NH3‒SCR activity. The resistance to SO2 and/or H2O in the long-term and multi-cycles and deactivation mechanism were investigated. We found that Zr-2 catalyst achieves a nearly 100% NOX conversion at 150~240 °C with or without SO2/H2O and nearly 100% NOX conversion and nearly 90% N2 selectivity in the long-term with SO2/H2O at 200 °C. Zr doping can inhibit the formation of N2O in NH3–SCR reaction, reduces the adsorption energy of O2, NO and NH3 on the catalyst, enriches catalyst surface acid sites and optimizes redox properties of catalyst. At the same time, doping of Zr does not prevent SO2 from being oxidized and reacting with NH3, but Zr doping can inhibit SO2 adsorption and accelerates (NH4)2SO4 decomposition at low temperature, thereby improving the resistance of catalyst to SO2. However, the coverage of sulfate changes redox properties, reduces adsorbed oxygen species and increases surface acidic strength, causing a decrease of activity.

Keywords: catalyst, perovskite, SCR, Mn, Zr