Fe and Mn mixed oxide catalysts supported on Sn-modified TiO2 for the selective catalytic reduction of NO with NH3 at low temperature†
Abstract
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 H2-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.