Study On The Catalytic Performance Of CO Oxidation For Ceria-containing Catalysts

Part I:This part investigated the effects of preparation methods(impregnation,co-precipitation and surfactant-assisted co-precipitation)on the structure,surface state,reducibility and CO oxidation activity of copper-ceria catalysts.The catalysts were characterized by XRF,XRD,LRS,N2 adsorption-desorption,HRTEM,XPS and H2-TPR.The obtained results suggested that the preparation methods exerted a great influence on the properties of copper-ceria catalysts:(1)compared with the catalyst prepared by impregnation method,the catalysts obtained from precipitation method(co-precipitation and surfactant-assisted co-precipitation)showed smaller grain size and higher BET surface area;(2)the catalyst derived from surfactant-assisted co-precipitation method displayed the highest activity for CO oxidation due to the highest concentration of oxygen vacancies as well as the highest contents of Ce3+ and Cu+,which improved the synergistic effect between copper and ceria.Thus the surfactant-assisted co-precipitation method was an effective method to obtain copper-ceria catalyst with high activity of CO oxidation.Part II:This part investigated the effects of cerium precursors[Ce(NO3)3 and(NH4)2Ce(NO3)6]on the structure,surface state,reducibility and CO oxidation activity of mesoporous CuO-CeO2 catalysts.The catalysts were characterized by TG-DTA,XRD,LRS,N2 adsorption-desorption,HRTEM,XPS,H2-TPR and in situ FT-IR.The obtained results suggested that the precursors exerted a great influence on the properties of CuO-CeO2 catalysts:(1)Compared with the catalysts from Ce(III)precursor,the derived Ce(IV)precursor catalysts showed smaller grain size,higher BET surface area,narrower pore size distribution,whereas their reducibility and activities were not enhanced.(2)In contrast,the catalysts from Ce(III)precursor without excellent texture displayed high reducibility and activities for CO oxidation due to the high content of Ce3+,following the redox equilibrium of Cu2+ + Ce3(?)Cu+ + Ce4+ shifting to right to form more stable Cu+ species,which was the origin of synergistic effect.The synergistic effect between copper and cerium was the predominant contributor to the improved catalytic activities of CuO-Ceo2 catalysts,instead of structural properties.Part III:This part investigated influence of cerium modification methods(impregnation and ion-exchange)on the gold dispersion,surface chemical states,synergistic effect between gold and cerium and CO oxidation activity of Au catalysts supported on Ce modified mordenites.The supports and catalysts were characterized by XRF,ICP,XRD,N2 adsorption-desorption,UV-vis spectroscopy,HRTEM,in situ FT-IR and XPS.In general,Ce-containing Au catalysts were found to be more active in CO oxidation than the Ce-free counterpart,with the impregnation method of cerium modification being more effective than the ion exchange method.The different catalytic performance of Ce-containing catalysts was related to multiple factors:(1)the impregnation method of cerium modification was more favorable to form Au particles with smaller size than the ion-exchange method,due to the higher ratio of surface Lewis acid sites.(2)The interface between Au and Ceo2 particles produced by impregnation method was more beneficial for the redox equilibrium of Au0 + Ce4+(?)Au3+ + Ce3+ to shift to right to form more active Au3+ species than the interface between Au particles and Ce cations produced by ion-exchange method,which enhanced the synergistic effect between gold and cerium and the catalytic performance of CO oxidation.