Investigation of the physicochemical properties and catalytic activities of Ce0.67M0.33O2(M = Zr4+, Ti4+, Sn4+) solid solutions for NO removal by CO

Abstract

NO removal by CO model reaction was investigated over a series of ceria-containing solid solutions, prepared by an inverse co-precipitation method, to explore the relationship between the physicochemical properties and catalytic performances of these catalysts. The synthesized samples were studied in detail by means of XRD, Raman, TEM, UV-Vis spectroscopy, N2-physisorption, H2-TPR, OSC, XPS and in situ FT-IR technologies. These results indicate that the incorporation of Zr4+, Ti4+ and Sn4+ into the lattice of CeO2 leads to a smaller grain size and enhanced reduction behavior. Furthermore, the catalytic performance test shows that the activities and selectivities of these solid solutions are higher than pure CeO2 and that the Sn4+-doped sample shows the best results. The reason may be that: (1) the decrease in grain size results in an enlargement of the BET specific surface area and an increase of surface Ce3+. The former is conducive for sufficient contact between the catalyst and reactant molecules and the latter contributes to the adsorption of COx species; (2) the enhanced reduction behavior is beneficial in generating more surface oxygen vacancies during the reaction process, which can weaken the N–O bond to promote the dissociation of NOx effectively. Finally, in order to further understand the nature of the catalytic performances for these samples, a possible reaction mechanism is tentatively proposed.