INTERACTION OF TITANIUM ISOPROPOXIDE WITH SURFACE HYDROXYLS ON SILICA

Six different silicas, (two aerosils, a hydrophobic aerosil, a silica gel, and Stöber spheres) pretreated at 423 K in vacuum were impregnated with Ti(Oi-Pr)4 in a N2 atmosphere and the excess alkoxide washed away in an inert environment. Infrared spectroscopy showed significant differences in the relative proportions of isolated and H-bonded surface hydroxyls on these silicas. The silicas that had a higher proportion of H-bonded hydroxyls picked up a greater amount of titania under our impregnation procedure. Using the route described above, the upper limit of loading appeared to be ≈3.0 Ti/nm2 on Stöber silica spheres, whose distinguishing feature was that the surface contained exclusively H-bonded hydroxyls. In situ infrared spectroscopy was also used to probe the interaction of the titanium alkoxide with the isolated as well as the H-bonded hydroxyls. On the basis of all of these experiments, we conclude that the hydroxyl groups that are capable of H-bonding with neighboring hydroxyls are the preferred adsorption sites, while the isolated hydroxyls are inert, at least at room temperature. © 1994 Academic Press, Inc.