The promotional mechanism of Nb addition on the activity and hydrothermal stability of CeZr2Ox catalyst for the selective catalytic reduction of NOx with NH3 (NH3-SCR) was investigated by various methods including N-2-physisorption, XRD, H-2-TPR and in situ DRIFTS. The Nb-promoted CeZr2Ox catalyst showed remarkable NH3-SCR activity together with excellent N-2 selectivity, SO2/H2O resistance and outstanding hydrothermal stability. The characterization results showed that the introduction of Nb to CeZr2Ox not only resulted in the high surface area and strong redox ability, but also promoted the adsorption and activation of NH3 and enhanced the reactivity of adsorbed nitrate together with NH3 species. All the above features were favorable for the superior NH3-SCR performance. In addition, the CeNb3.0Zr2Ox catalysts hydrothermally aged below 800 degrees C still possessed high redox ability and abundant acid sites, all of which were responsible for the excellent hydrothermal durability. The novel CeNb3.0Zr2Ox catalyst was a promising candidate for the removal of NOx from diesel engine. (C) 2015 Elsevier B.V. All rights reserved.