钛硅复合氧化物局域结构的研究

The Local Structure of Titania-Silica Composite Oxides

用 XAFS(X-ray absorption fine structure)分析了由溶胶-凝胶、液相浸渍和化学气相沉积等三种方法制备的二氧化钛和二氧化硅复合氧化物的 Ti K 边结构．结果表明：溶胶-凝胶法制得的复合氯化物中的钛分散很好，液相浸渍法次之，而化学气相沉积法最差，不论哪种方法，随钛含量(或钛硅原子比)的增加，边前特征峰 A2降低，钛的第一配位层 Ti-O 的配位数和键长增加；在复合载体中既有钛中心对称的八面体6配位 TiO_6的结构也有钛中心对称性差的四面体4配位 TiO_4或五面体5配位结构，并且随钛含量增加，钛的局域结构越来越接近锐钛矿型二氧化钛，根据 XAFS、XRD、IR 表征结果，提出了钛硅复合氧化物模型。

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.