Mesoporous silica-alumina aerogels with high thermal pore stability through hybrid sol-gel route followed by subcritical drying

Abstract

Silica-alumina mixed oxide aerogels have been synthesised for the first time by subcritical method, having compositions of 5, 10, 15, 20 and 25 wt.% of alumina in silica through a hybrid sol-gel technique. Boehmite was used as the precursor for alumina and TEOS for silica. Subcritical drying method involving repeated solvent exchange and gel wall strengthening is followed in place of supercritical method. The aerogels are calcined at 500, 700, 900 and 1200 degrees C. Nitrogen sorption studies indicate that the mixed oxide aerogels are mesoporous in nature with high surface areas comparable to supercritically dried aerogels and also possess excellent thermal pore stability. FT-IR spectroscopy has been used to study the effect of an alumina addition to silica. The linear shrinkage of aerogels upon heat treatment is also reported. The acid strength distribution has been measured by temperature programmed desorption of ammonia (TPD). The present method involving hybrid sol-gel route followed by subcritical drying could be further developed for synthesis of mixed oxide mesoporous hybrids for catalyst and gas adsorption.