A series of cobalt supported on Zr1-xCexO2 catalysts were synthesized by citrate complexation method (CC-series) and impregnation method (IM-series) and their catalytic performance of the NO oxidation to NO2 were tested. CC-series exhibited higher catalytic activity than IM-series. These prepared samples were characterized by various techniques such as XRD, Raman spectroscopy, BET, TEM, H-2-TPR, UV-vis DRS and XPS. CC-series was found to possess easier reducibility, lower crystallite size and higher relative amount of Ce3+ compared with IM-series, which in turn led to their higher catalytic activity. The effect of Ce/Zr ratio on the catalytic activity of samples was also investigated. The results showed that adding large amount of Zr into Co/CeO2 system had a negative effect on the activity because of the corresponding decreasing of the surface Ce3+ concentration which was related with the production of oxygen vacancy. (c) 2015 Elsevier B.V. All rights reserved.