Univ Sci & Technol China, Dept Chem Phys, Hefei 230026, Peoples R China
; Inst High Energy Phys, Synchrotron Radiat Lab, Beijing 100039, Peoples R China
A series of Pt/BaAl2O4-Al2O3 NOx trap samples were prepared by coprecipitation-impregnation method. The supports BaAl2O4-Al2O3 were calcined at 800 degreesC and 1000 degreesC, respectively. X-ray Diffraction (XRD), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure(EXAFS) were used to characterize the microcosmic structure of barium and platinum species in the samples. It is shown that the barium exists in the forms of BaAl2O4 and BaCO3 crystallites. With the decreasing of calcination temperature and barium content, the dispersion of BaAl2O4 phase becomes higher. Platinum in the samples mainly exists as small atomic clusters, which possess very high dispersion. In comparison with the standard compound of platinum, the magnitude for Pt-Pt coordination shell is significantly decreased, and the coordination distance is also shortened about 0.01 nm. All the results suggest that the BaAl2O4 crystallites should be the centers for NOx storage, while the fine-grained platinum species with high dispersion are deduced as the centers for the capture and oxidation of NOx species.