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/Sn_xTiO₂ 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/Sn_xTiO₂ was transformed from anatase to rutile completely, which enhanced the stability of the mesoporous structure. The FeMn/Sn_0.05TiO₂-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/Sn_0.05TiO₂ 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/Sn_0.05TiO₂ 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.