CeO2/WO3-TiO2 (CeWTi) and Nb2O3-CeO2/WO3-TiO2 (NbCeWTi) catalysts were prepared by a sol-gel precipitation method. Both the catalysts exhibit high selective catalytic reduction of NOx with NH3 (NH3-SCR) activities at 270-500 degrees C. The sulfur tolerances of the catalysts were evaluated at 270 degrees C by adding H2O and SO2 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 Cex+ active sites effectively from attacking of SO2. According to the results of temperature-programmed desorption of ammonia (NH3-TPD), H-2 temperature-programmed reduction (H-2-TPR) and SO2 oxidation, loading niobia on CeWTi inhibited the SO2 oxidative adsorption and SO3 production which basically reduced sulfur poisoning of the catalyst Additionally, the niobia modification ensured the formation of nitrates from the competitive adsorption of SO2 and hereby facilitated the nitrate SCR route based on the in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS).