A comprehensive study on sulfur tolerance of niobia modified CeO2/WO3-TiO2 catalyst for low-temperature NH3-SCR

CeO 2 /WO 3 -TiO 2 (CeWTi) and Nb 2 O 5 -CeO 2 /WO 3 -TiO 2 (NbCeWTi) catalysts were prepared by a sol-gel precipitation method. Both the catalysts exhibit high selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) activities at 270–500 °C. The sulfur tolerances of the catalysts were evaluated at 270 °C by adding H 2 O and SO 2 in the feeding gas and NbCeWTi exhibited a significantly improved resistance. The thermogravimetric (TG) and mass spectrographic (MS) results indicated that much less sulfates formed on NbCeWTi and existed mainly in the form of ammonium hydrogen sulfate species which protected Ce x+ active sites effectively from attacking of SO 2 . According to the results of temperature-programmed desorption of ammonia (NH 3 -TPD), H 2 temperature-programmed reduction (H 2 -TPR) and SO 2 oxidation , loading niobia on CeWTi inhibited the SO 2 oxidative adsorption and SO 3 production which basically reduced sulfur poisoning of the catalyst. Additionally, the niobia modification ensured the formation of nitrates from the competitive adsorption of SO 2 and hereby facilitated the nitrate SCR route based on the in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS).