Fe and Mn mixed oxide catalysts supported on Sn-modified TiO2 for the selective catalytic reduction of NO with NH3 at low temperature

Although FeMn/TiO2 catalysts possessed a good low-temperature activity, their poor SO2 resistance remained a serious issue. This report explores the use of Sn as an additive to modify TiO2 supports for the synthesis of FeMn/SnxTiO2 catalysts with excellent SO2 resistance. The results showed that the doping of Sn in TiO2 could improve the SO2 tolerance and low-temperature SCR activity significantly. When the Sn/Ti molar ratio was higher than 0.05, the crystal phase of TiO2 in FeMn/SnxTiO2 was transformed from anatase to rutile completely, which enhanced the stability of the mesoporous structure. The FeMn/Sn0.05TiO2-S catalyst possessed a relatively high specific surface area even after exposure to the SO2 resistance test for 3 h. The H-2-TPR, XPS and TG results showed that Sn doping improved the redox properties, and the amounts of Mn4+ and surface chemisorbed oxygen, which were beneficial for improving the low-temperature activity. Furthermore, Sn doping could also effectively inhibit the formation of sulfates on the surface of the FeMn/Sn0.05TiO2 catalyst in the SO2 resistance test. The in situ DRIFTS results revealed that Sn doping could obviously suppress SO2 adsorption on the surface of the FeMn/Sn0.05TiO2 catalyst. Meanwhile, it enhanced the adsorption of NH3 species on the Lewis acid sites, which was also beneficial for improving the low-temperature activity. As the interactions and comparative adsorption between SO2 and NH3 on the active sites had been allivated, this resulted in the SCR reactions proceeding via the Eley-Rideal (E-R) mechanism through a nearly normal pathway over the Sn-modified FeMn/TiO2 catalyst.