Silanol chemistry in siliceous faujasite

Abstract

The importance of silanol chemistry in the adsorption and catalytic applications of amorphous silica gel is well documented. Increased utilization of crystalline, high surface area silicas may require a better understanding of the formation and reactions of the silanol group in crystals. Several different types of silanols have been formed in siliceous (< 150 ppm A1) faujasite by dealumination using SiCl 4 plus aqueous HCl washes. Surface and internal silanols have been characterized by NMR, thermogravimetric analysis, IR, neutron and X-ray diffraction. The internal silanols can be removed by thermal treatment. Surface, and to some extent internal, silanols react with reagents such as trimethylsilyl chloride (Me 3SiCl).