The Synthetic Research Of Advanced Ceria Based Materials In The Application Of Emission Control Catalysis

Recently,the technology of vehicle emission control attaches more and more public attemtions.And the development of new ceria base materials with good hydrothermal stability and oxygen storage capacity was one of the hot point in this field,which might benefit the confliction between vehicle industry and environment.In this work,the synthetic procedure of ceria was carefully optimized,and the trade-off between stability and activity of nano ceria were discussed.In the second chapter,the optimization of ceria synthesis process was briefly introduced.The process of concentration of reactant,crystallization process,drying and pore control were investigated,and optimized based on the BET surface area of cera before/after calcination.The results indicated that,a atmospheric pressure crystallization process induced best impact to the sample surface area,which brings up to 2~3 fold higher surface area after 700 ? calcination,comparing with the one without crystallization.Besides,by combining the organic additives and spray drying process,the surface area after calcination was further improved for 20 %.In the third chapter,the sample property(stability and oxygen storage capacity)prepared with 0,1,3 and 6 days crystallization were compared.The sample structure was characterized by XRD(for crystalline phase),H2-TPR(for surface reducibility),XPS(surface valency),DRIFTS(IR absorption)and HR-TEM(for the micro-structure of crystallines).And the results indicate that 1)the crystallization process improves the hydrothermal stability of ceria in expense of oxygen storage capacity,induced by lowered the concentration of surface defect and 3)the formation of disordered crystalline interface.In the fourth chapter,the kinetics of oxygen storage/release of the sample prepared with 0,1,3 and 6 days crystallization were compared.The results indicated that crystallization treatment decreased the initial rate of oxygen release,but increased the total amount of available oxygen.Agreed with the result of XPS,it infers that the surface defect(oxygen vacancy)was removed by crystallization.In the fifth chapter,the influence of crystallization to the crystalline growth in aging condition was investigated by kinetic method.The samples(0,1,3 and 6 days crystallized)were aged at 720,750 and 780 ? for 0~20 h,and the crystalline growth isotherms were fitted by four models.The results indicated that the activation energy of crystalline growth changed increased from ~120 k J/mol to ~200 k J/mol as crystallization time prolonged,and this had a linear correlation with the energetic state of mismatch crystalline interface(calculated from DRIFT spectra).Therefore,the improved hydrothermal stability induced by crystallization was attributed to the formation of interface.In the sixth chapter,ceria-alumina bicomposite was prepared by a so called molecular mixing method,which extended the application of ceria to higher temperature.By mixing ceria with alumina in different ratio,the sample resisted up to 90 m2/g BET surface area and comparable oxygen storage capacity(to common ceria)after 1050 ?,10 h hydrothermal aging.Further study indicated that ceria crystalline dispersed in the alumina framework uniformly,which brings the good property to this material.