Studies of the dispersion state of CuO on TiO₂ and CeO₂-TiO₂ and activity for NO+CO reaction

Abstract

The activities of CuO supported on TiO₂ and ceria-modified TiO₂ in catalyzing the NO reduction by CO have been examined with a microreactor-GC NO+CO reaction system, and the catalysts characterized by physical adsorption, TPR, XRD and NO-TPD. The CuO/TiO₂ and CuO/CeO₂ -TiO₂ catalysts increase the NO reduction by CO, probably due to the surface dispersed CuO and fine CuO crystallites. Pore structure data show that the pore size distribution of TiO₂ is mainly as micro-pores and meso-pores, and the adsorption-desorption isotherm is the type IV of BDDT classification. TPR profiles indicate that Cu-Ti has four TPR peaks, α peak from highly dispersed CuO species, β peak from oxide clusters with a

structure similar to CuO, γ peak from CuO crystallites and δ peak from the interaction of CuO and TiO₂, TiO₂ surface oxygen reduction. In addition, the phase change of TiO₂ doesn't show negative influence in catalytic activities. Among the tested catalysts, the catalyst with 12% CuO loading has the highest activity for NO+CO reaction, but at CuO loading of <img src='http://www.niscair.res.in/jinfo/greaterequal.gif' border=0>3%, a crystallite of CuO has already been formed, which means that besides highly dispersed CuO, the CuO crystallite also plays an important role in NO+CO reaction, and the catalytic activities have a close relation with the CuO crystallite size and its micro structure data. NO-TPD profile also shows that the catalytic activities are closely related to NO dissociation – a rate-determining step for the NO+CO reaction, but are not affected by the amount of adsorbed NO.