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

XAFS分析表明，低钛含量的二氧化钛样品中的钛处于四面体(TD)环境中，而高钛含量的样品中的钛处于八面体(OH)环境中。以叔丁基氢过氧化氢为氧化剂，Td-Ti对辛基-1-烯生成环氧化物具有较高的催化活性。通过在二氧化钛-二氧化硅表面引入氧气，观察到了超氧离子的EPR谱。在Td-Ti和OH-Ti上形成的超氧化物的g值不同，钛含量对这些光谱的影响与XAFS分析的结果相似。因此，XAFS技术很好地反映了二氧化钛-二氧化硅的表面状态。少量掺杂到二氧化硅基质中的Zr和Nb也呈TD构型，对环氧化物的生成具有活性。因此，在反应的第一步，液态环氧化一般通过过氧化氢与配位的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.