Enhancement of Ce doped La–Mn oxides for the selective catalytic reduction of NOx with NH3 and SO2 and/or H2O resistance

Cerium modified La–Mn oxides for NH3–SCR at low temperature is prepared by one–step synthesis method and characterized. The results showed that the perovskite La–Mn oxides at A–bit doped by Ce is more favorable for NOx removal than B–bit doping and achieves about 80% conversion of NOx at 120°C and about 100% in the range temperature of 180–220°C as well as good SO2 and/or H2O resistance. However, LaMn0.8Ce0.2O3 (B–bit doping) has better N2 selectivity than La0.8Ce0.2MnO3 (A–bit doping) and LaMnO3. The generated N2O and NO2 influence the N2 selectivity in the NH3–SCR reaction, but N2O is from the NH3 oxidation while NO2 is from the NO oxidation. The perovskite La–Mn oxides at A–bit or B–bit doped by Ce are able to maintain the perovskite structure of LaMnO3.15 but the exposed plane shifts from (104) to (110). However, for both doped samples, some CeOx and Mn3O4 are spilled out from the perovskite structure of La–Mn oxides. A–bit ions doped by Ce can increase Mn4+ relative content, specific surface area, available oxygen and surface acid amount, while B–bit doping decreases Mn4+ relative content and adsorbed oxygen and increases Ce4+ relative content. After SO2 resistance testing, the formation of (NH4)2SO4 and MnSO4 on all catalysts is inevitable, but the binding force of the formed metal sulfate is different on catalyst surface, resulting in the difference of its resistance to sulfur.