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 CO_x 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 NO_x effectively. Finally, in order to further understand the nature of the catalytic performances for these samples, a possible reaction mechanism is tentatively proposed.