Grafting Titanocene on Hydrophilic Amorphous Silica:Synthesis of an Effective Catalyst for Olefin Epoxidation

Ti/silica catalysts were prepared by grafting titanocene dichloride (Cp₂TiCl₂) on hydrophilic amorphous silica with different Ti contents under mild conditions. The results of FT-IR, UV-vis and XPS analyses proved that titanium was successfully grafted in the form of Ti(IV) on amorphous silica and the maximum content of Ti grafted was found to be ca. 3 wt.%. When cyclohexene epoxidation with TBHP was carried out over these synthesized catalysts, both the activity and the selectivity to epoxide increased with the amount of Ti grafted. This amorphous Ti/silica catalyst showed a higher activity and a higher selectivity to epoxide than Ti-containing molecular sieves, Ti-MCM-41 and Ti-beta, with nearly the same Ti content. With Ti content larger than 3 wt.%, however, anatase phase (TiO₂) was formed to give a lower activity and selectivity to epoxide.