FORMATION OF MICROPOROUS SILICA-GELS FROM A MODIFIED SILICON ALKOXIDE .1. BASE-CATALYZED GELS

Base-catalyzed silica gels have been prepared from mixtures of TEOS and a modified silicon alkoxide, methyltriethoxysilane. The ratio of modified ester to TEOS was varied in order to study the effect on gel structure. Low level additions of the modified ester resulted in an increase in the surface area of dried gels, but higher additions caused a decrease in the accessible area. This decrease in surface area corresponds to a significant change in physical morphology as probed with small angle X-ray scattering. Si-29 MAS-NMR was used to determine the Q and T distributions of the gels and to estimate surface area and skeletal density based on the terminal group size. As the methyltriethoxysilane content was increased, the fraction of T3 and T2 species increased and the difference between the nitrogen surface area (accessible) and 'Q-derived' (total) surface area increased. Adsorption of carbon dioxide, methane, and water at 298 K was also measured.