The identity in atomic structure and performance of active sites in heterogeneous and homogeneous, titanium-silica epoxidation catalysts

The nature of the Ti(IV) active site in heterogeneous titano-silica epoxidation catalysts is shown to be same as that of a Ti(IV)-centered site bound to soluble homogeneous silsesquioxane catalysts. A range of techniques, encompassing pre- and near-edge X-ray absorption spectroscopy and molecular dynamics calculations, provides quantitative information pertaining to the four-coordinated site that is tripodally anchored to silica. The catalytic performance of a series of engineered active sites in [(c-C5H9)(7)Si7O12TiOXPh3], where X = Si, Ge, or Sn, shows that the order of enhancement is Ge > Sn > Si. This is compared with previously published(7) performances of engineered active sites in solid titano-silicate catalysts. The key importance of accessibility to the four-coordinated Ti(IV) site is highlighted here.