FTIR Study of the Adsorption and Thermal Behavior of Vinyltriethoxysilane Chemisorbed on γ-Al₂O₃

Abstract

The adsorption and thermal stability of vinyltriethoxysilane (VTES) was studied on a γ-Al2O3 surface. Adsorption occurs near room temperature with the production of ethanol from the reaction with isolated surface AlOH groups, producing the surface species AlOSi(OC2H5)2CHCH2. As the surface is heated, decomposition of AlOSi(OC2H5)2CHCH2 occurs first via loss of the OC2H5 groups (starting at ∼520 K) and then with loss of the CHCH2 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 Al2O3 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, SiOH infrared bands are observed to develop as AlOH 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.