Univ Sci & Technol China, Dept Chem Phys, Hefei 230026, Anhui, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
Under lean-burn conditions, the NO, trap Pt/Ba-Al-O can store NO, as nitrates or nitrites. Successive sequences of lean and rich operating periods provide a high efficiency for NO, reduction. On addition of the Co promoter, the NO, storage capacity of the trap is improved remarkably. In this paper, the NO, 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 Xray absorption fine structure were used to characterize the microstructure of the samples. After calcination at 800degreesC I cobalt species react with alumina to form CoAl2O4, in which cobalt is present in the form of tetrahedrally-coordinated Co2+ ions. The well-dispersed CoAl2O4 phase can promote the conversion of NO to NO2 through reactions of 2Co(2) + 1/2O(2) --> 2Co(3) + [O2-] and 2Co(3+) + [O2-] + NO --> 2Co(2+) + NO2 under lean-burn conditions. This results in an enhancement of the NO, 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 strung interaction between Pt species and supports is inhibited. This leads to the adequate distribution of fine-grained platinum species over the NO, trap and is favorable for NO, storage. A NO, storage capacity of 372 mumol/g is obtained over Pt/Co-Ba-Al-O at 200 degreesC, which is about 21.6% higher than that over Pt/Ba-Al-O.
; Chemistry, Physical
; Engineering, Chemical