Structure of ceria-based mixed oxides and its influence on HCl catalytic oxidation performance

The physiochemical properties of ceria-based mixed oxides(Ce_0.9M_0.1O₂, M=Cu, Cr, Zr, Ti and La) prepared by ammonia co-precipitation method were characterized by XRD, Raman, N₂ adsorption-desorption, ESEM and H₂-TPR. The performances of catalysts for gas-phase HCl catalytic oxidation to Cl₂ were also investigated. The results showed that the incorporation of Cu, Cr and Zr could greatly reduce the grain size of ceria-based mixed oxides, leading to a higher surface area and pore volume, and enhance the reduction of oxygen species at low temperature. While more surface oxygen vacancies and improved reduction of oxygen species at high temperature could be obtained in Ce_0.9Ti_0.1O₂ and Ce_0.9La_0.1O₂. The changed structure and surface property of mixed oxides showed a significant influence on its HCl catalytic oxidation performance, the order of the activities of various ceria-based mixed oxide catalysts at 430℃ was as follows: Ce_0.9Cu_0.1O₂ > Ce_0.9Cr_0.1O₂ > Ce_0.9Zr_0.1O₂ > Ce_0.9Ti_0.1O₂ > CeO₂ > Ce_0.9La_0.1O₂. The number of oxygen species reduced at low temperature was directly related to its catalytic activity. kinetic studies showed that the catalysts with more reduction of oxygen species at low temperature provided more active sites for HCl adsorption and activation, while the oxygen vacancies were conducive to the adsorption and activation of gas-phase oxygen.