FTIR Study of the Adsorption and Thermal Behavior of Vinyltriethoxysilane Chemisorbed on γ-Al 2 O 3

The adsorption and thermal stability of vinyltriethoxysilane (VTES) was studied on a γ-Al 2 O 3 surface. Adsorption occurs near room temperature with the production of ethanol from the reaction with isolated surface Al OH groups, producing the surface species Al O Si(OC 2 H 5 ) 2 CH CH 2 . As the surface is heated, decomposition of Al O Si(OC 2 H 5 ) 2 CH CH 2 occurs first via loss of the OC 2 H 5 groups (starting at ∼520 K) and then with loss of the CH CH 2 groups (starting at ∼820 K). Below 375 K, ethanol is the sole gas phase product produced, and near 520 K, both ethanol gas and ethylene gas are produced. At higher temperatures, ethanol decomposes on the surface and ethylene is the only gas phase species present. The thermal stability of ethoxy groups on the VTES-treated Al 2 O 3 surface decreases considerably under strong hydrolysis conditions in water vapor. There is also a decrease in the stability of the vinyl groups under strong hydrolysis conditions. Above ∼525 K, Si OH infrared bands are observed to develop as Al OH groups disappear. Above ∼1100 K, organic ligands are no longer detected on the surface by FTIR spectroscopy and the surface remains covered with a silicate overlayer.