Pore size and liquid impregnation of microporous aluminosilicate gels and glasses

Optically clear monolithic (OCM) gels of microporous aluminosilicates have been prepared by slow hydrolysis-polycondensation of alkoxides. Subsequent heating induces transformations into OCM microporous glasses. The surface area (∼610 m²/g after drying at 300°C) and the pore volume (∼0.35 cc/g at 300°C) decrease monotonously with increasing annealing temperature. However, after heat treatment at 600°C under air (glass state) the monoliths are still microporous. Modifications of the xerogel pore distribution by an impregnation process and metal aggregate formation with pyrolysis are studied by N₂ adsorption-desorption analysis and small-angle X-ray scattering (SAXS). The microporous structure becomes mesoporous. A model of microporous impregnation in the gel or glass state is proposed.