Effect of ZrO 2 addition on CuO/TiO 2 activity in the NO+CO reaction

Abstract

The activities of CuO/TiO 2 and ZrO 2-modified CuO/TiO 2 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/TiO 2 were 280 °C at T 50% and 450 °C at T 99%, compared to 325 °C at T 99% for 6% CuO–10% ZrO 2/TiO 2. The 6% CuO–10% ZrO 2/TiO 2 calcined at 500 and 750 °C had similar catalytic activities ( T 99% at 300 °C) 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 ZrO 2 addition, the diffraction peak of ZrO 2 was not detected and the diffraction peak intensity of CuO did not increase either, likely due to the strong interaction between CuO and ZrO 2 that enhanced the catalytic activity and stability. In the H 2 atmosphere, CuO produced dispersed Cu 0 species. Four desorption species (NO, N 2O, N 2 and O 2) were detected during the thermal desorption of NO by CuO/TiO 2 and CuO–ZrO 2/TiO 2 treated in both air and H 2. Addition of ZrO 2 onto CuO/TiO 2 shifted the NO dissociation peaks towards low temperature, indicating that the activity of NO decomposition was higher by CuO–ZrO 2/TiO 2 than by CuO/TiO 2. The NO+CO reaction formed intermediary product N 2O 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.