The activities of CuO/TiO2 and ZrO2-modified CuO/TiO2 in the NO reduction by CO were examined with a microreactor-gas chromatography (GC) NO + CO reaction system, and the catalysts were characterized by physical adsorption, TG-DTA, XRD and NO-TPD techniques. The results showed that the NO conversion temperatures of 6% CuO/TiO2 were 280degreesC at T-50% and 450degreesC at T-99%, compared to 325degreesC at T-99% for 6% CuO-10% ZrO2/TiO2. The 6% CuO-10% ZrO2/TiO2 calcined at 500 and 750degreesC had similar catalytic activities (T-99% at 300degreesC) in H-2 atmosphere. The nitrogen adsorption-desorption isotherm and pore-size distribution curve of Tio(2) represented type IV of the BDDT system and a typical mesoporous sample, respectively. After ZrO2 addition, the diffraction peak of ZrO2 was not detected and the diffraction peak intensity of CuO did not increase either, likely due to the strong interaction between CuO and ZrO2 that enhanced the catalytic activity and stability. In the H-2 atmosphere, CuO produced dispersed Cu-0 species. Four desorption species (NO, N2O, N-2 and O-2) were detected during the thermal desorption of NO by CuO/TiO2 and CuO-ZrO2/TiO2 treated in both air and H-2. Addition of ZrO2 onto CuO/TiO2 shifted the NO dissociation peaks towards low temperature, indicating that the activity of NO decomposition was higher by CuO-ZrO2/TiO2 than by CuO/TiO2. The NO + CO reaction formed intermediary product N2O at low temperature but formed N-2 at high temperature. In addition, the peak temperature of NO desorption was related to the catalytic activity under both air and H-2, and the dissociation of NO on catalysts surface was a rate-determining step in NO + CO reaction. (C) 2004 Elsevier B.V. All rights reserved.