An IR study of the chemistry of triethoxysilane at the surface of metal oxides

The interaction of triethoxysilane (TES) with the surfaces of silica, silica–alumina, alumina, titania, zirconia and magnesia, all activated by outgassing at 773 K (973 K for silica), has been studied by FTIR spectroscopy. In all cases, TES weakly adsorbs in a molecular form and later reacts with surface OHs giving rise to a species bonded to the surface with a single SiOSi bond. Only at higher temperatures further condensation occurs giving rise to doubly- and triply-bridged species. On ionic oxides, a disproportionation reaction is evident giving rise to hydrogensilicate or silicate species at 473–573 K. The use of TES and of triethoxyalkylsilanes to modify the surfaces of oxides is briefly discussed.