荧光XAFS表征Pt/BaAl2O4-Al2O3催化剂中的微量铂物种

随着稀薄燃烧(lean-burn)发动机的推广使用和环保法规的日趋严格,消除稀燃尾气中的氮氧化物(N O x)已刻不容缓。N O x储存还原技术被认为是最具应用前景的方法之一1,2]。目前,对Pt/BaA l2O4-A l2O3体系中N O x储存与还原机制的研究较多1￣4],但对该体系中微量铂物种微观结构及其与性能的关系研究较少,这主要是由于Pt含量(0.1w t%￣0.5wt%)太低,分散度较高,使表征方法受到很大限制。本文采用共沉淀-浸渍法制得具有较高比表面积和热稳定性的N O x储存还原催化剂Pt/BaA l2O4-A l2O3,应用荧光X-射线吸收精细结构方法(Fluores-cence-…

Fluorescence-XAFS Characterization on the Small Amount of Platinum in Pt/BaAl2O4-Al2O3 Catalysts

The support BaAl₂O₄-Al₂O₃ and the catalysts Pt/BaAl₂O₄-Al₂O₃ were prepared by co-precipitation and impregnation method, respectively. The NO_x storage capacities (NSC) of the samples were investigated. The fluorescence-XAFS technique was employed to characterize the fine structures of the small amount of platinum. The results show that after calcination in air, the platinum mainly exists as chloride, and the rest is in the form of oxychloride, however, after reduction by H₂, the most platinum species transform into highly dispersed metallic crystallite (2~3 nm) with a very small residual amount of chloride. After aging treatment, a small part of platinum in the reduced sample is oxidized into oxide. Combined with the results of the NO_x storage capacities, it is indicated that for NO_x storage, highly dispersed metallic platinum crystallites are the most active phase, while the chloride species of platinum have much weaker effect on NO_x storage. The growth of Pt crystallite size and the partial oxidation of metallic Pt are the main reasons for the decrease of NO_x storage capacity of the aged sample.