Binary metal oxides CuO-CoOx supported on Ce0.67Zr0.33O2 (denoted as CZ, thereafter) catalysts had been characterized by XRD, LRS, UV-DRS, IR, TPR, in situ FT-IR and activity test for the removal of NO by CO. Results suggested that (1) both copper oxide and cobalt oxide (loadings <= 0.5 and 0.32 mmol/100 m(2) CZ, respectively) were highly dispersed on CZ support; (2) the addition of cobalt species promoted the reduction of the dispersed copper oxide, and improved the activity of copper oxide supported on CZ due to the strong interaction between active copper oxide and cobalt oxide, which was dependent on the preparation procedure and the cobalt oxide content; (3) the reduction of NO by CO over these catalysts went through different mechanisms at low and high temperatures, which was related to the change of the active species during the reaction process; (4) the introduction of cobalt oxide altered the adsorption type of NO and CO on these catalysts, and oxidized the NO dimers into ionic NO3-1. A possible reaction mechanism was proposed to discuss the NO + CO reaction based on all these results. (C) 2009 Elsevier B.V. All rights reserved.