Studies on some novel silica molecular sieves

Four different silica end members of zeolites (zeosils) namely silica-ZSM-48, silica ZSM-22, silica-ferrierite and silica-ZSM-5 have been synthesized and their structural features and properties determined. Long chain polyamines act as templates for the formation of silica-ZSM-22 and silica-ZSM-48. The use of amines with side NH₂ groups or straight chain amines at elevated temperatures, favours the formation of silica-ZSM-48. Ethylenediamine-boric acid pair acts as a template for silica-ferrerite formation while the use of highly branched tertiary mines leads to the formation of silica-ZSM-5. Available data indicate that these four zeosils are isostructural with the corresponding zeolites. These molecular sieves contain 3-dimensional 4-connected network of corner linked [SiO₄] tetrahedra, possessing channel like voids. Silica-ZSM-22 and silica-ZSM-48 contain 1D channel systems but the latter has wider channels. Silica-ferrierite possesses 2D channels while silica-ZSM-5 possesses a 3D channel system. All these frameworks are thermally stable upto 1000⁰C, even after the removal of templates. They are hydrophobic, organophyllic and possess neither catalytic nor ion exchange properties.