Microporous Crystalline Titanium Silicates

Publisher Summary This chapter focuses on the microporous crystalline titanium silicates. Titanium containing materials have been investigated for various reactions, but selective oxidations with H2O2 as the oxidant have attracted the most interest. For these reactions, the formation of surface titanium peroxo compounds with H2O2 and the subsequent transfer of the peroxidic oxygen to the organic reactants have been proposed to explain the mechanism by which titanium participates in the catalytic cycle. H2O2 has the advantage of giving environmentally benign water as its by-product. Furthermore, H2O2 ranks first in terms of available oxygen in the list of oxygen donors.The unusual properties of titanium silicalites have been attributed to the presence of TiIV in framework positions of the SiO2 lattice. It is important to realize that there is a limit to the extent of substitution; the exact value is still under discussion, but is certainly not more than a few percent. Very likely, the structure of crystalline silica is not stable at higher degrees of substitution. The discovery of the new titanium silicates and of their catalytic properties in H2O2 oxidation reactions has had a major impact in catalytic science and its industrial applications.