Particulate sol-gel route for microporous silica gels

The preparation of microporous silica gels from particulate as opposed to polymeric suspensions of silica using alkylsilicates as precursors is described. The pore structure of this silica gel is determined mainly by the size and the packing geometry of the silica particles. Fast hydrolysis, slow condensation and low solubility all contribute to a high supersaturation level and result in the formation of small particles. Particles formed under acidic conditions are smaller than those obtained under basic reaction conditions due to the slower condensation rate and lower solubility in acid. At the same pH, alkylsilicates having smaller alkyl groups react faster with water leading to smaller primary particles. During the sol to xerogel transformation process, the pH of the sol, together with the time of aging, play important roles in determining the pore structure of the final product.