Mechanistic investigation of the enhanced NH(3)-SCR on cobalt-decorated Ce-Ti mixed oxide: In situ FTIR analysis for structure-activity correlation

Available online 16 July 2016A series of transition metals (Co, Cu and Fe) were selected to decorate Ce-Ti mixed oxide to elevate the low-temperature activity of selective catalytic reduction of NOx by NH3 (NH3-SCR) reaction, by adjusting the ratio of surface Ce3+ species and oxygen vacancies. Among them, Co-Ce-Ti sample exhibited the excellent low-temperature activity and broadened temperature window, which could be attributed to the improvement of the physico-chemical properties and the acceleration of the reactions in the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Owing to the different ionic sizes of Co2+ and Ce4+, the lattice distortion of Ce-Ti mixed oxide was greatly aggravated and subsequently increased the ratio of Ce3+ and the surface adsorbed oxygen, which benefited the generation of adsorbed NOx species and improved the reaction in the L-H mechanism. Meanwhile, the coordinatively unsaturated cationic sites over the Co-Ce-Ti sample induced more Lewis acid sites and enhanced the formation of the adsorbed NH3 species bounded with Lewis acid sites, which were considered as the crucial intermediates in E-R mechanism, and therefore facilitating the reaction between the adsorbed NH3 species and NO molecules. The enhancements in both the reactions from L-H and E-R mechanisms appeared to directly correlated with the improved deNOx performance on the Co-Ce-Ti sample, and the L-H mechanism could be the dominate one at low temperatures due to its rapid reaction rate.Jie Liu, Xinyong Li, Qidong Zhao, Jun Ke, Huining Xiao, Xiaojuan Lv, Shaomin Liu, Moses Tadé, Shaobin Wan