Effects of SiO2 modification on the hydrothermal stability of the V2O5/WO3–TiO2 NH3-SCR catalyst: TiO2 structure and vanadia species

Abstract

To investigate the effects of silica modification on the hydrothermal stability of the V₂O₅/WO₃–TiO₂ catalyst, the catalysts were hydrothermally treated at 650 °C and 750 °C in 10 vol% H₂O/air for 24 h. The fresh and aged catalysts were characterized by nitrogen physisorption (BET), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), temperature-programmed reduction of H₂ (H₂-TPR) and temperature-programmed desorption of NH₃ (NH₃-TPD). Based on the experimental results, it is assumed that Si⁴⁺ ions enter the TiO₂ lattice to form Si_xTi_1−xO₂ solid solutions, which could inhibit the agglomeration of titania crystallites and anatase-to-rutile phase transition. These advantages of Si doping can essentially benefit the hydrothermal stability of V₂O₅/WO₃–TiO₂ catalysts. The decrease of the SCR performance upon ageing is due to the extensive loss of surface area and evolution of vanadia species. Our observations show that the doped catalysts are stable at temperatures below 650 °C and the inactive V_xTi_1−xO₂ phase and crystalline V₂O₅ form on the catalysts upon hydrothermal ageing at 750 °C.