The Research On The Performance Of CeO₂-ZrO₂-Al₂O₃ Composite Materials

To improve the thermal stability of texture and structure of CeO₂-ZrO₂ compounds and simplify the preparing process of catalyst, in recent years, CeO₂-ZrO₂-Al₂O₃ compounds have been prepared by Al₂O₃ with high special surface area and CeO₂ with excellent OSC. It is of great interest to further study CeO₂-ZrO₂-Al₂O₃ compounds for improvement of three-way catalyst property.In this paper, to further study CeO₂-ZrO₂-Al₂O₃ (CZA) compounds, seven series of CZA samples have been prepared. To confirm CZA holding good structural thermal stability, CeO₂, CeO₂-Al₂O₃ (CA), CeO₂-ZrO₂-Al₂O₃ (CZA), ZrO2-Al₂O₃ (ZA), Al₂O₃ and ZrO₂ have been prepared, and the influence of additives Y³⁺, La³⁺ and alkaline earth have been studied on the performance of CZA. In this paper, research was focused on the performance of Ce_xZr_1-xO₂/Al₂O₃ system materials with different Ce/Zr, and the property of low-CeO2 CZA and high-CeO₂ CZA with different Al₂O₃ contents. And The influence of aging time have been researched on the performance of CZA. The samples'textural properties, oxygen storage capacities, phase composition, and redox behavior were characterized by BET, oxygen pulse adsorption, X-ray diffraction (XRD), Raman, SEM and H2-temperature programmed reduction technique (H₂-TPR).The results indicate that CZA system materials hold excellent structural thermal stability among CA, CZA and ZA. Y³⁺, La³⁺ doped into CZA can improve CZA textural performance whose best additive quantity is 2-4wt % , and CZAYLa>CZALa>CZAY in thermal stability. Similarly, alkaline earth doped into CZA can also improve pore volume and textural thermal stability, and the effect of doping MgO and SrO is the best among alkaline earth. For Ce_xZr_1-xO₂/Al₂O₃ system materials, the fresh and aged samples all present single homogeneous phase and no phase separation occur, and the samples (Ce/Zr<1) hold good reducible capacity, OSC , textural performance and thermal stability. For low-CeO2 CZA system materials, with Al₂O₃ contents increasing, the main phases of fresh and aged samples can both keep single homogeneous cubic fluorite lattice, but after 1000℃calcination, the sample with 60wt% Al₂O₃ contents, begins to occur phase separation andγ-Al₂O₃ phase was detected. Among high-CeO₂ CZA samples, the sample with 60wt% Al₂O₃, have best textural performance and thermal stability. Aging time have a great influence on thermal stability of CZA materials and for CZA, the best aging time is 24h.