Abstract

Inelastic electron tunneling spectroscopy (IETS) has been used to obtain vibrational spectra of alkoxysilanes adsorbed on aluminum oxide. The spectra reveal that: (1) monoalkoxysilanes are not adsorbed whereas trialkoxysilanes are readily adsorbed, (2) the reaction mechanism of triethoxysilanes and trimethoxysilanes is the same, and (3) the reaction mechanism under anhydrous conditions utilizes surface OH or OD groups present on alumina. These results support the hypothesis that the alkoxy groups exchange with OH groups on the surface to form siloxane bonds, and that these bonds are stabilized with trialkoxysilanes. For monoalkoxysilanes, either the bonds do not form so readily, or they are not stabilized by further condensation of the adsorbed species. Instead, the monoalkoxysilanes appear to catalyze further oxidation of the alumina surface.

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