Activity Improvement of Mn/Al₂O₃ for NH₃-SCR Reaction via the Rare-Earth (Ce, La, Nd and Y) Oxides Modification

A series of rare-earth (Ce, La, Nd, and Y) oxides doped Mn/Al2O3 catalysts were prepared by the impregnation method and used for the selective catalytic reduction (SCR) of NOx with NH3. The additions of rare-earth oxides greatly enhance the SCR catalytic activity of Mn/Al2O3, and the highest activity was obtained over CeMn/Al2O3 with a NOx conversion higher than 85% at 125-300 degree celsius. The results of characterization show that the rare-earth oxides additives except for Y2O3 promote the surface distribution of Mn element and enhance the ratio of chemisorbed oxygen and Mn4+ on the surface of Mn/Al2O3. Moreover, with the introduction of rare-earth oxides, the reducibility of MnO2 species is improved and a larger amount of the weak acid sites are obtained. The increase in the ratio of Mn4+ and the enhancement in the reducibility of MnO2 are the main reasons for the elevation in SCR activity of the rare-earth oxides modified Mn/Al2O3 catalysts. This study sheds light on the promotional effect of rare-earth oxides over the Mn-based catalysts for SCR reaction. [GRAPHICS] .