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《Chinese Journal of Catalysis》 2001-04
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Effect of Ceria on Pd/γ-Al_2O_3 Three-Way Catalysts

TU Jing, FU Yilu *, LIN Peiyan (Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China)  
The effect of ceria (CeO 2) doping to the Pd/γ-Al 2O 3 catalyst on its three-way catalytic activity was investigated. When the Pd content is not more than 1 0%, the increase of Pd content is of benefit to the activity. The thermal stability and activity of catalysts in lean conditions are significantly promoted by pre-doping the alumina support with an appropriate amount of CeO 2 before the palladium impregnation in catalyst preparation. Under the reaction conditions of 0 1% NO, 0 15% C 3H 6, 1 5% CO and 1 37% O 2 in N 2 balance, and space velocity (SV)=30?000 h -1 , the light-off temperatures T 50 (the temperature at 50% conversion) of NO, C 3H 6 and CO over the aged 1 0%Pd/15%CeO 2-Al 2O 3 sample were 41, 41 and 56 ℃, respectively, lower than those over the aged 1 0%Pd/Al 2O 3 sample. Overmuch CeO 2 in Pd/CeO 2-Al 2O 3 brings on a decline in the thermal stability. It is also discussed that the synergy between Pd and CeO 2 enhances the activity of the catalysts. The surface structure of the Pd/CeO 2-Al 2O 3 catalyst was studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption-mass spectrum (TPD-MS) of NO adsorption after O 2 adsorption. It is confirmed that the presence of CeO 2 makes Pd 2+ in catalyst precursors easier to be reduced to Pd 0 by hydrogen flow at 450 ℃. TPD-MS results indicate that there is a stronger dissociation adsorption of NO on the Pd/CeO 2-Al 2O 3 than on the Pd/Al 2O 3. There is a higher Pd dispersion in Pd/CeO 2-Al 2O 3 than in Pd/Al 2O 3.
【Fund】: 国家自然科学基金 ( 2 99730 37);; 安徽省自然科学基金 ( 990 45 42 9)资助项目
【CateGory Index】: O643.3
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