Hydrothermal and sulfur aging of CeTi/CeWTi catalysts for selective catalytic reduction of NO_x with NH_3

The CeO₂-TiO₂ (CeTi) and CeO₂/WO₃-TiO₂ (CeWTi) catalysts were prepared by sol-gel method. The as-prepared catalysts were hydrothermally treated at 760 °C for 48 h in air containing 10 vol% H₂O to obtain the hydrothermal aged catalysts. The sulfur aged catalysts were treated at 400 °C with 100 ppm SO₂, 10% water vapor, air balance for 48 h and catalysts. The powder X-ray diffraction (XRD) and Raman results indicate that the crystallization of hydrothermal aged catalysts is more serious than sulfur aged catalysts. In addition, tungsten species can stabilize the CeTi catalyst from grain growth. According to the results of in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS), temperature-programmed desorption of ammonia (NH₃-TPD), H₂ temperature-programmed reduction (H₂-TPR) and ammonia oxidation, the aging process leads to loss of surface area, redox properties, surface acidities and surface ceria concentration, especially for the hydrothermal aging. The NH₃-NO/NO₂ SCR performances of sulfur aged catalysts are better than that of hydrothermal aged catalysts. Compared with CeTi catalyst, the addition of tungsten inhibits the crystallization of catalyst. So that more acid sites and active sites are retained. This is also the reason why tungsten addition improves the NH₃-NO/NO₂ SCR performance of CeTi catalyst.