MODIFICATION OF THE SURFACES OF SILICA, SILICA-ALUMINA, AND ALUMINUM SILICATE WITH CHLOROTRIMETHYLSILANE

The solid and gaseous products from the silation of powdered silica, g ranular silica, silica-alumina, and aluminum silicate have been determ ined for a range of reaction conditions. In all cases HCl was produced , as expected. Unexpectedly, lesser but significant quantities of meth ane were also produced at temperatures over 200 degrees C. During sila tion of silica at 250 degrees C methane is briefly the only gaseous pr oduct, followed by copious production of HCl and a decreasing proporti on of methane. This sequence of events suggests that initially the rea ction is dominated by irreversible chemisorption at highly active site s and that reaction of hydroxyls with the chlorosilane to produce HCl occurs only after the highly active sites are consumed. Silation of al uminosilicates differs from that expected from the additive effects of the surface Al-OH and Si-OH, demonstrating that the surface of the mi xed support is modified compared to those of each component. Silation of a commercial silica-alumina catalyst support was very similar to th at of alumina, indicating that the surface properties of this material are alumina-like and do not resemble an aluminum silicate.