Synthesis Of CeO₂-Al₂O₃ Composite Oxide And Study Of Catalytic Performance

CeO2 is a important rare earth material and it is widely used in three-way catalyst because of its important oxygen storage capacity (OSC). Synergistic effect between CeO2 and precious metal is beneficial for catalytic performance for promoting the release and reduction of oxygen. However, palladium catalysts supported on pure ceria decline fast at high temperature due to loss of surface area and oxygen storage capacity with sintering of precious metal. Al2O3 material presents large surface area and good property resistance to high temperature sintering.Thus, to take advantage of the Al2O3 material, supporting ceria on alumina or coating ceria with alumina can significantly improve the thermal stability of CeO2. However, different ceria-alumina composite manner has a significant impact on structure, texture and performance of CeO2-Al2O3 composite oxides and CeO2-Al2O3-supported Pd catalysts. So the effect of different composite manner on CeO2-Al2O3 composite oxides and CeO2-Al2O3-supported Pd catalysts is studied in order to provide a reference for development of three-way catalyst.In order to study the interaction between the carrier and the precious metal, catalysts were characterized by XRD, N2 physical adsorption, H2-TPR, O2-TPD, SEM, O2 pulse chemisorption, CO-TPD-MS and other various techniques.This paper discussed how the preparation method of carrier CeO2, ceria-alumina composite manner and CeO2 composition affect the properties of catalysts. The main work is as follows:(1) CeO2 materials were synthesized by four methods (precipitation p, precipitation-hydrothermal method p-h, decomposition d, hydrothermal method h). Four CeO2-supported palladium catalysts were prepared and investigated for CO oxidation reaction. It is demonstrated that the ceria prepared by hydrothermal method presents largerst surface area, smallest particle size of all. The stable PdO species and the number of the surface lattice oxygen are favourable for enhancement of CO oxidation activity in Pd/Ce-h catalyst.(2) The ceria-alumina composite oxides with different composite manner were prepared by various methods in different precipitation sequence. The ceria-alumina-supported Pd catalysts were Pd/Ce/Al, Pd/AlCe and Pd/Al/Ce. Ce/Al was synthesized by supporting ceria on alumina. Pd/Ce/Al was synthesized by wet impregnation of Ce/Al exhibits the best catalytic activity. It is mainly due to a strong interaction between precious metal and Ce/Al, leading to stronger mobility of lattice oxygen and more activated surface oxygen than Pd/AlCe and Pd/Al/Ce catalysts.(3) The specific surface area and activity of the ceria-alumina-supported Pd catalysts decrease after calcination at 800℃. The activity of Pd/Ce/Al sample is best, which is affected by mobility of lattice oxygen.(4) A series of Pd/xCeAl (x=10,20,30,40) catalysts were prepared with different amount of ceria. It is demonstrated that Pd/30CeAl catalyst presents the best catalytic performance with the light-off temperature about 81.5℃. It is mainly due to the more reducible CeO2 species on the surface and the better reducibility of Pd/30CeAl than the other three catalysts.