Control of Fine Structure of Group IVb and VB Metals By the Template Function of Silica and Invention of New Reaction Systems

Ti、Zr和Nb被引入到SiO2四面体基体中，并借助SiO2的模板作用控制它们的配位状态，XAFS分析表明，低Ti含量的TiO 2-SiO2样品中的Ti处于四面体（Td）环境，而高Ti含量的样品中的Ti处于八面体（Oh）环境。以叔丁基过氧化氢为氧化剂，Td-Ti催化1-辛烯氧化生成环氧化物具有很高的活性。通过在钛硅表面引入氧，观察到超氧阴离子的EPR谱。在Td-Ti上形成的超氧化物的g值不同于在Oh-Ti上形成的超氧化物的g值，并且Ti含量对这些光谱的影响与通过XAFS分析观察到的相似。XAFS技术较好地反映了钛硅复合材料的表面状态，少量的Zr和Nb掺入到SiO2基体中也呈Td-构型，对环氧化物的形成有促进作用。因此，液相环氧化通常在反应的第一步中通过氢过氧化物与配位不饱和金属离子的配位进行。

Ti, Zr, and Nb were incorporated into the silica tetrahedral matrix, and their coordination state was controlled with an aid of the template action of the silica.XAFS analysis revealed that the Ti in titania-silica with low Ti content was in the tetrahedral (Td) environment and that in the high Ti content sample in the octahedral (Oh) environment. Td-Ti exhibited high activity to produce epoxide from oct-1-ene using t-butyl hydroperoxide as an oxidant. EPR spectra of superoxide oxide ion were observed by introducing oxygen on the surface of titania-silica. The g-value of the superoxide formed on Td-Ti was different from that on Oh-Ti and the effect of Ti content on these spectra was similar to that observed by the XAFS analysis. Thus XAFS technique well reflects the surface state of the titania-silica.Zr and Nb incorporated into silica matrix with a small amount level also took Td-configuration and was active for epoxide formation. Thus, the liquid-phase epoxidation generally proceeds through the coordination of hydroperoxide to the coordinatively unsaturated metal ion in the first step of the reaction.