Hu Tiandou

NO x 储存催化剂Pt/BaAl 2 O 4 -Al 2 O 3 的XAFS研究

采用共沉淀-浸渍法在不同载体焙烧温度下,制备了不同Al/Ba原子比的Pt/BaAleO4-Al2Os系列样品.用XRD,XANES,EXAFS,以及NSC(NOxstorage capacity)测定等手段对样品的微观结构和NOx储存性能进行了详细的表征.样品中Ba物种是以BaAl2O4和BaCO3两种混合物相的形式存在,且伴随着载体焙烧温度和Ba含量的降低,BaAl2O4物相的分散度变高,NOx储存活性也随之提高,这表明BaAl2O4相的分散度与样品的NOx储存性能密切相关,小颗粒的BaAl2O4相是NOx的主要储存活性中心.在样品中,Pt物种以金属原子簇形式存在,分散度很高,其Pt-Pt壳层配位数较标样Pt粉有显著下降,Pt-Pt键长变短,出现了纳米收缩现象.高分散的小颗粒金属Pt原子簇为捕获和氧化NOx的主要活性中心.

The Local Structure of Titania-Silica Composite Oxides

By analyzing the X-ray absorption spectra of Ti K edge, the structural information of TiO2-SiO2 composite oxides prepared by sol-gel(CTS1, CTS4), impregnation (SYB02, SYB04, SYB06), and CVD (CVD], CVD2) methods were obtained. TiO2 was most dispersed in SiO2 by the sol-gel method and TiO2 was least dispersed in SiO2 by the CVD method. The pre-edge structure of anatase(Ti K edge of XAFS) is characteristic of three peaks: A1, A2, and A3. For the sol-gel and impregnation prepared TiO2-SiO2 supports, the structure of Ti K edge is different from that of anatase. The intensity of A2 peak increases with the decrease of the content of Ti, and coordination numbers of the first shell of Ti - O increase with the increase of the content of Ti. The pre-edge absorption feature of TiO2-SiO2 prepared by CVD is consistent with that of anatase, and the coordination number of the first shell is nearly to 6. The bond lengths of the first shell of Ti - O increase with the increasing Ti content. The results were confirmed by further measurement using XRD. Based on the experimental results, a model of titania-silica composite oxide was proposed.

Local structure information by EXAFS analysis using two algorithms for Fourier transform calculation

The present work is a comparison study between different algorithms of Fourier transform for obtaining very accurate local structure results using Extended X-ray Absorption Fine Structure technique. In this paper we focus on the local structural characteristics of supported nickel catalysts and Fe3O4 core-shell nanocomposites. The radial distribution function could be efficiently calculated by the fast Fourier transform when the coordination shells are well separated while the Filon quadrature gave remarkable results for close-shell coordination.

XRD AND EXAFS INVESTIGATION OF THE DECOMPOSITION OF Co-Cu SOLID SOLUTION PREPARED BY MELT SPINING

High solid-solubility Co15Cu85 alloys were prepared by melt spining and then submitted to isothermal and anisothermal annealing to obtain granular alloys. The synchrotron radiation x-ray diffraction patterns and extended x-ray absorption fine structure (EXAFS) spectra were measured to investigate the decomposition of supersaturated solid solution upon annealing. Experimental results indicated the precipitation of ultrafine Co-rich particles occurred at about 500°C and the annealing had a great influence on the middle-range order of Co atoms. While the fitted EXAFS spectra showed that the interfaces of Co precipitates seem to be enriched with vacancy-type defects, leading to distorted interfaces.

First Performance Test at BEPC X-Ray Absorption Fine Structure Station

The foundation of the first synchrotron radiation x-ray absorption fine structure (XAFS) station in China has been completed and the station was ready for transmission XAFS experiment. This paper reports the first XAFS spectrum recorded in this station and the result of performance test centered on the intensity, energy dispersion and energy accuracy of the beam line in this station.