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The CeO2, Ce-Nb-Oxand Nb2O5catalysts were synthesized by citric acid method to investigate the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH3. The catalytic activity measurements indicate that the mixed oxide Ce-Nb-Oxpresents a higher SCR activity than the single oxide CeO2or Nb2O5catalyst. In addition, the Ce-Nb-Oxcatalyst shows a high resistance towards H2O and SO2at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H2results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH3results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce-Nb-Oxcatalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce-Nb-Oxcatalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situDRIFT experiments suggest that both NH3on Lewis acid sites and NH4+on Brønsted acid sites can react with NO species, and adsorbed NO and NO2species can both be reduced by NH3. In the SCR process, O2as an important role primarily acts as the accelerant to improve the redox and acid cycles. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance. more...