【摘要】 采用共沉淀 浸渍法制备了Pt/Co Ba Al O催化剂 ,用X射线衍射、X射线吸收近边结构和扩展X射线吸收精细结构等手段表征了催化剂的微观结构 ,并在连续流动微型反应器上测定了催化剂对NOx 的储存性能 .载体经过 80 0℃焙烧后 ,Co物种主要以四面体配位的铝酸钴相存在 .在富氧条件下 ,高分散的小颗粒铝酸钴相促进了NO向NO2 的转化 ,大大改善了催化剂对NOx 的储存性能 .铂物种则以小的金属原子簇形式存在 ,分散度很高 .钴助剂的添加改善了氧化铝相的分散度 ,抑制了金属铂原子簇与载体的相互作用 ,使铂在催化剂表面分散得更均匀 ,从而有利于NOx 的储存更多还原

【Abstract】 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.更多还原