REACTIONS OF TETRAETHOXYSILANE VAPOR ON POLYCRYSTALLINE TITANIUM-DIOXIDE

The reactions of tetraethoxysilane (TEOS) vapor on dehydroxylated and water predosed polycrystalline TiO2 were studied by Fourier transform infrared spectroscopy (FTIR) and temperature-programmed desorption (TP D). Exposure at 300 K leads to dissociative adsorption producing a mon oethoxysilyl ligand and surface ethoxide species. The ethoxide ligands react and desorb in the range 450-650 K as gas phase ethanol and ethy lene, while the monoethoxysilyl ligand decomposes at similar to 650 K to gas phase ethanol and ethylene and surface bound SiO2. Dissociation of TEOS on TiO2 is not affected by water predose; although, a greater amount of ethanol is produced in the gas phase at 550-650 K, and the SiO2 which is formed exhibits vibrational features characteristic of a hydroxylated species. TEOS chemistry on TiO2 was compared to, the ads orption and reaction of ethanol on the same surface. Adsorption of eth anol at 300 K yielded surface ethoxide species which desorbed in two s tates as the parent alcohol and ethylene; desorption was also centered at 450 and 650 K. These results complement and supplement our previou s study of TEOS on a TiO2(110) single crystal surface.