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《Chinese Journal of Catalysis》 2002-05
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Effect of Cobalt Promoter on Structure and Properties of Lean-Burn NO_x Trap Pt/Ba-Al-O

LI Xingang 1, MENG Ming 1, LIN Peiyan 1, CHEN Jiafu 1, FU Yilu 1*, YU Shouming 1, XIE Yaning 2, HU Tiandou 2(1 Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, Anhui, China; 2 Institute of High Ener  
Under lean-burn conditions, the NO x trap Pt/Ba-Al-O can store NO x as nitrates or nitrites. Successive sequences of lean and rich operating periods provide a high efficiency for NO-%x% reduction. On addition of the Co promoter, the NO x storage capacity of the trap is improved remarkably. In this paper, the NO x trap Pt/Co-Ba-Al-O with an Al∶Ba∶Co molar ratio of 32∶2∶1 and a Pt: Co-Ba-Al-O mass ratio of 1.0% was prepared by the coprecipitation-impregnation method. X-ray diffraction, X-ray absorption near edge structure and extended X-ray absorption fine structure were used to characterize the microstructure of the samples. After calcination at 800 ℃, cobalt species react with alumina to form CoAl 2O 4, in which cobalt is present in the form of tetrahedrally-coordinated Co 2+ ions. The well-dispersed CoAl 2O 4 phase can promote the conversion of NO to NO 2 through reactions of 2Co 2++1/2O 2 2Co 3++ and 2Co 3+++NO 2Co 2++NO 2 under lean-burn conditions. This results in an enhancement of the NO x storage capacity. Pt species mainly exist as well-dispersed small atomic clusters. Compared with the sample Pt/Ba-Al-O, Pt/Co-Ba-Al-O shows a higher alumina dispersion and the strong interaction between Pt species and supports is inhibited. This leads to the adequate distribution of fine-grained platinum species over the NO x trap and is favorable for NO x storage. A NO x storage capacity of 372 μmol/g is obtained over Pt/Co-Ba-Al-O at 200 ℃, which is about 21.6% higher than that over Pt/Ba-Al-O.
【Fund】: 国家自然科学基金 ( 2 99730 37);; 教育部优秀青年教师资助计划 (EYTP);; 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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