Factors governing the synthesis of zeolites from silicoaluminate hydrogels : a comparative study of the crystallization mechanisms of zeolites Y, mordenite and ZSM-5

Abstract

The syntheses of zeolites Y, mordenite and ZSM-5 have been systematically investigated. All crystallization processes can be explained by assuming direct hydrogel transformation (or surface nucleation) (ZSM-5 type B), aqueous phase ion transportation (mordenite, ZSM-5 type A), or by a combination of these two mechanisms (zeolite Y). The characterization of the liquid and solid precursors and intermediate phases has been carried out mainly by multinuclear NMR spectroscopy. The influence of tetraalkylammonium salts addition on the synthesis of zeolite Y is discussed in terms of structure-directing effects of the organic cations and supersaturation of the zeolite-forming species.