Effects of SiO2 Modification on the Hydrothermal Stability of the V2O5/WO3-TiO2 NH3-SCR Catalyst: TiO2 Structure and Vanadia Species

To investigate the effects of silica modification on the hydrothermal stability of the V2O5/WO3-TiO2 catalyst, the catalysts were hydrothermally treated at 650 degrees C and 750 degrees 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 H-2 (H-2-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 SixTi1-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 degrees C and the inactive VxTi1-xO2 phase and crystalline V2O5 form on the catalysts upon hydrothermal ageing at 750 degrees C.