Highly efficient NH3-SCR of NOx over MnFeW/Ti catalyst at low temperature: SO2 tolerance and reaction mechanism

Abstract

The W modified MnFe/Ti composite oxide catalyst was proposed and tested for low-temperature SCR of NOx by NH3, which possesses excellent SCR activity, N2 selectivity and SO2 tolerance compared with MnFe/Ti catalyst. The physicochemical properties of MnFeW/Ti catalyst were comprehensively characterized by N2 physisorption, XRD, Raman, XPS, NH3-TPD and H2-TPR. The transport of oxygen and electron became more facile during SCR reaction as a result of the formation of Mn-O-W and Fe-O-W bonds, which was beneficial to maintain the Mn4+, Fe3+ and chemisorbed oxygen at high relative concentrations and thus accelerated the SCR reaction rate. The appropriate acidity and redox property improved NOx conversion and N2 selectivity. The in situ DRIFTS results suggested that the surface acidity was tuned via the W doping, leading to that the SCR reaction obeys only Eley − Rideal mechanism. The TG-MS results and DRIFTS spectra revealed that the oxidation of SO2 can be inhibited by restraining the transfer of electrons from SO2 to Mn4+ and Fe3+, which reduced the formation of metal sulfates. Therefore, the MnFeW/Ti catalyst exhibits strong SO2 tolerance at low temperature.