The promotional role of Nd on Mn/TiO2 catalyst for the low-temperature NH3‑SCR of NOx

A series of rare-earth metal doped 30% Mn-3% RE/TiO2 (RE = Ce, Sm, Nd, Er, Y) catalysts were prepared by adopting two step incipient wetness impregnation method and investigated for the low-temperature SCR of NOx with NH3. It was found that 3% of rare earth elements (Nd, Er, Y) was added to 30% Mn/TiO2 catalyst even could increase the catalytic performance at the low temperature, in addition to usual used Ce and Sm. And the promoting effect of Nd was among the most significant. Then the 30%Mn-3%Nd/TiO2 catalyst was synthesized by another two methods, Coprecipitation and Sol-gel, for a comparative study. Various techniques were applied to characterize the catalysts. The catalysts prepared by Coprecipitation and Sol-gel method exhibited higher surface area and smaller average particle size in comparison with catalyst prepared by impregnation with TiO2 support. The addition of Nd made surface area and dispersion of MnOx species increase. It also led both the content of amorphous MnO2 and the content of crystalline Mn2O3 to decrease, but the proportion of MnOx species with low oxidation state increased. H2-TPR results showed that the low temperature reduction peak of MnOx was shifted to much lower temperatures with the doping of Nd, which improved the redox property of the catalysts. The all characteristics shown above could well explain the promotional role of Nd doping in the 30%Mn-3%Nd/TiO2 catalyst, that improved the low temperature SCR catalytic activity.