Effects of atmospheres and precursors on MnO x /TiO2 catalysts for NH3-SCR at low temperature

The effects of atmospheres and precursors on MnO _x /TiO₂ catalysts were studied, which were prepared by the impregnation method and tested for their NO _x conversion activity in ammonia selective catalytic reduction (NH₃-SCR) reactions. Results showed that the manganese carbonate (MC) precursor caused mainly Mn₂O₃, while the manganese nitrate (MN) precursor resulted primarily in MnO₂ and the manganese sulfate (MS) precursor was unchanged. The manganese acetate (MA) precursor leaded obtaining a mixture of Mn₂O₃ and Mn₃O₄. NO _x conversion decreased in the following order: MA/TiO₂ > MC/TiO₂ > MN/TiO₂ > MS/TiO₂ > P25, with a calcination temperature of 773 K in air. Catalysts that were prepared by MA and calcined in oxygen performed strong interaction between Ti and Mn, while MnTiO₃ was observed. Compared to the catalysts calcined in nitrogen, those calcined in oxygen had larger diameter and smaller surface area and pore. Catalysts that were prepared by MA and calcined in nitrogen tended to gain higher denitration rates than those in air, since they could be prepared with significant specific surface areas. NO _x conversion decreased with calcination atmospheres: Nitrogen> Air> Oxygen. Meanwhile, amorphous Mn₂O₃ turned into crystalline Mn₂O₃, when the temperatures increased from 673 to 873 K.