Ceria-based catalysts exhibit excellent performance at mediate-high temperature in selective catalytic reduction (SCR) of NO with NH3. However, their activities are severely restrained in the presence of H2O and SO2. In this work, Ni-Ce-La composite oxide nanocrystals were synthesized. After sulfation, it showed excellent H2O and SO2 tolerance. The catalysts were studied by inductively coupled plasma (ICP), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature-programmed desorption (TPD), in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), Brunauer-Emmett-Teller (BET) surface area and thermogravimetry (TG). The H2O and SO2 tolerance of Ce-based catalysts and sulfation mechanism and its effect on the SCR activity were investigated. After sulfation, the increase in proportion of Ce3+/(Ce3+ + Ce4+, the formation of SO42- and the increase of NH3 adsorptivity all illustrate that sulfation increases the Bronsted acid sites of samples. The mainly reserved Lewis acid sites and the newly formed Bronsted acid sites contribute to the excellent SCR activity. A shrinking core model was proposed to explain the process of sulfation. The reaction process mostly follows L-H mechanism. After sulfation, Ni-Ce-La composite oxide increases NH3 adsorptivity and remains good NO adsorptivity, which greatly enhances resistance to H2O and SO2. (C) 2016 Elsevier B.V. All rights reserved.