Catalytic activities of CuO/TiO2 and CuO-ZrO2/TiO2 in NO + CO reaction

Abstract

CuO/TiO2 and CuO-ZrO2/TiO2 catalysts with different CuO loadings were prepared by the impregnation method using Cu(NO3)2 and Ce(NO3)3 aqueous solutions of desired concentrations. The catalytic activities in NO+CO reaction were investigated, and the structural and reductive properties of various CuO/TiO2 and CuO-ZrO2/TiO2 catalysts were characterized by means of BET, TPR, XRD and NO-TPD technology. It was found that after treatment in H2 at 500 °C for 2 h, the catalytic activities were improved dramatically compared with treatment in normal air at 500 °C for 2 h. The NO conversion temperature (T99%) was 325 °C for 6% CuO/TiO2 and 300 °C for 6% CuO-10% ZrO2/TiO2, and their activities increased with increase in ZrO2 loading. There were four TPR peaks in CuO/TiO2 and two TPR peaks in CuO-ZrO2/TiO2, indicating that addition of ZrO2 caused changes in CuO species on TiO2. The air-treated catalysts displayed CuO diffraction peaks, whereas the H2-treated catalysts displayed Cu metal diffraction peaks. Four desorption species (NO, N2O, N2 and O2) were detected during the thermal desorption of NO by CuO/TiO2 and CuO-ZrO2/TiO2 treated in both air and H2. There were two adsorption states of nitric oxide (NO) on the catalyst’s surface, i.e. desorption species at low temperature on the weak sites and at high temperature on the strong sites. Addition of ZrO2 onto CuO/TiO2 shifted the NO dissociation peaks towards low temperature, which means 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 N2 at high temperature. In addition, the peak temperature of NO desorption corresponded with the catalyst’s activity under both air and H2, and the dissociation of NO on catalyst surface was a rate-determining step in NO+CO reaction.