Mesoporous silica from rice hull ash

In the synthesis of mesoporous materials, the use of a template with an adequate porosity is normally favoured. As far as silica is concerned, many sophisticated procedures directed towards this goal have been published. It is already well documented that rice hull contains relatively pure silica after combustion of the residual organic matter. The authors of this contribution have recently demonstrated that large surface area silicates react with glycerol around 200 °C to give depolymerized silica with a chemical composition similar to that of poly‐alkoxides. The interest in this so‐called depolymerization is to allow easy formation of reactive gels which retain the memory of the porous structure of the original starting material. Rice hull ash (RHA), obtained after combustion of the organic residues at 500 °C, gives a silica characterized by mesopores with an average diameter about 3.5 nm. It is shown that RHA reacts with glycerol at 200 °C to form gels which, after hydrolysis and calcination, retain the mesoporous character. The hydrolysis procedure and especially, the pH is important for the distribution of the mesoporosity. The very simple reaction of a by‐product of the food industry with glycerol, a “green reagent”, gives a mesoporous solid silica in the form of a reactive gel, with many potential uses. Its use in a new procedure for the synthesis of a supported ZSM‐5 zeolite has been demonstrated. Copyright © 2007 Society of Chemical Industry