Research Of Alumina Doped Ceria-Zirconia Mixed Oxides With Co-precipitation Method

As the substrate and catalytic stimulater, ceria-zirconia and alumina play an important part in the automotive exhaust three-way-catalyst. At present, the hot issues about three-way-catalyst was was alumina doped ceria-zirconia mixed oxides, which can improve the thermal stability and the oxygen storage capacity of ceria-zirconia solid solution to alleviate the periodic fluctuate of the A/F as the exhaust gas composition rapidly oscillates between hydrocarbon-rich and hydrocarbon-poor mixtures.In this paper, three kinds of alumina doped ceria-zirconia mixed oxides were prepared by co-precipitation method with the aim of evaluating the effects of different mixing ways to OSC performance and thermal stability of alumina doped ceria -zirconia mixed oxides. Both fresh and aged samples were characterized on home -made dynamic OSC measure instrument. Structure analysis, element analysis and so on were also done by XRD, TEM, BET, XPS, H2-TPR and EPR.Alumina doped ceria-zirconia solid solution still kept the fluorite cubic structure of ceria-zirconia solid solution. Alumina doping can improve the dynamic oxygen storage capacity of ceria-zirconia solid solution. The high thermal stability was also improved. Atomic mixing ceria-zirconia-alumina sample exhibited excellent perfor- mance on high thermal stability and OSC capacity.By the structural, textual characterization and OSC measurement, ACZ mixing ways (atomic mixing, molecular mixing and mechanically mixing) obviously affected the thermal stability and OSC capacity of the samples, where the atomic mixing samples performed the best. For the effects of alumina on CZ, structure variation occurred on the atomic and molecular mixing samples. CeAlO3 was detected in the XRD patterns of the atomic and molecular mixing samples after reducing treatment. The existence of surface Ce³⁺ species facilitate the thermal stability of alumina.Results showed that: The interaction between alumina and ceria-zirconia should be taken into apart. Incorporation of Al³⁺ to the ceria lattice or Al³⁺ existence make the ceria-zirconia lattice distortion, which lead to more oxygen vacancies creation and high mobility of bulk oxygen. Some Ce³⁺ cations occupied the vacant octahedral coordinated sites on the surface of alumina, the occupation of octahedral site by Ce³⁺ might block the tetrahedral to octahedral sites under high temperature treatment.