Influence of solvent in the synthesis steps of titanium-supported amorphous silica epoxidation catalysts

A series of titanium-silica catalysts with relatively low Ti contents were prepared by dispersing titanium isopropoxide in a solvent (cyclohexanol, 1-phenylethanol, 1-hexanol, 2-(2-ethoxyethoxy)ethanol, diglyme, and acetophenone) and then mixing each solution with the silica substrate. The process consisting of the hydrolysis of the Ti precursor by the hydroxyl groups of the silica surface yielded catalysts containing Ti loadings of 0.8–3.0 wt%. The catalysts prepared were characterized using various spectroscopic techniques, including diffuse reflectance infrared Fourier transform (DRIFTS), ultraviolet–visible (UV–vis), and photoelectron (XPS) spectroscopic techniques. The catalytic activity of the catalysts studied was determined using liquid-phase epoxidation of 1-octene with hydrogen peroxide as a model reaction. All catalysts showed very high hydrogen peroxide consumption but the selectivity to the epoxide was seen to be strongly dependent upon the solvent used in the preparation. Only the catalyst prepared using cyclohexanol solvent, in which the titanium content was low (0.8 wt%) and the Ti(IV) ions were isolated tetrahedrally coordinated by oxide anions, exhibited very high (95%) selectivity to the epoxide. The other Ti/SiO2 catalysts containing a higher amount of titanium (1.0–3.0 wt%), but less disperse and with Ti(IV) in an octahedral environment, exhibited poor performance in the target reaction.