钛硅复合氧化物局域结构的研究

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TiO6的结构也有钛中心对称性差的四面体4配位TiO4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.

The Local Structure of Titania-Silica Composite Oxides

By analyzing the X-ray absorption spectra of Ti K edge,the structural information of TiO_2-SiO_2composite oxides prepared by sol-gel(CTS1,CTS4),impregnation(SYB02,SYB04,SYB06),and CVD(CVD1,CVD2)methods were obtained.TiO_2 was most dispersed in SiO_2 by the sol-gel method and TiO_2 was least dis-persed in SiO_2 by the CVD method.The pre-edge structure of anatase(Ti K edge of XAFS)is characteristic ofthree peaks:A1,A2,and A3.For the sol-gel and impregnation prepared TiO_2-SiO_2 supports,the structure of Ti Kedge is different from that of anatase.The intensity of A2 peak increases with the decrease of the content of Ti,andcoordination numbers of the first shell of Ti-O increase with the increase of the content of Ti.The pre-edge ab-sorption feature of TiO_2-SiO_2 prepared by CVD is consistent with that of anatase,and the coordination number ofthe first shell is nearly to 6.The bond lengths of the first shell of Ti-O increase with the increasing Ti con-tent.The results were confirmed by further measurement using XRD.Based on the experimental results,a model oftitania-silica composite oxide was proposed.