In situ FT-IR was employed to investigate CO or/and NO interaction with CuO supported on Ce0.67Zr0.33O2 (hereafter denoted as CZ) catalysts. The physicochemical properties of CuO-CZ were also Studied by combination of XRD, TPR and NO + CO activity tests. The results indicated that the dispersed CuO species were the main active components for this reaction. The catalysts showed different activities and selectivities at low and high temperatures, which should be resulted from the reduction of dispersed copper oxide species. This reaction went through different mechanisms at low and high temperatures due to the change of active species. FT-IR results suggested: (1) CO was activated by oxygen originating from CZ support, which led to surface carbonates formation, and partial dispersed CuO was reduced to Cu+ species above 150 degrees C; (2) NO interacted with the dispersed CuO and formed several types of nitrite/nitrate species, whereas crystalline CuO made little contribution to the formation of new NO adsorbates; (3) NO was preferentially adsorbed on CuO-CZ catalysts compared with CO in the reactants mixture. These adsorbed nitrite/nitrate species exhibited different thermal stability and reacted with CO at 250 degrees C. As a result, a possible mechanism was tentatively proposed to approach NO reduction by CO over CuO-CZ catalyst. (C) 2009 Elsevier B.V. All rights reserved.