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Crystallization of Sub-Micrometer Sized ZSM-5 Zeolites in SDA-Free Systems

The seed-induced crystallization system has been adopted for the synthesis of sub-micrometer sized zeolite ZSM-5 in the absence of organic structure directing agent (SDA). The structural (phase purity), particulate (sizes and morphologies) and chemical compositions (framework Si/Al ratios) of the crystalline end products could be well controlled via the variation of synthesis parameters such as size and amount of silicalite-1 seed nanocrystals, batch alkalinity, excess of sodium ions and ageing of reaction mixtures. More importantly, the crystallization mechanism has also been revealed as a typical linear, size-independent growth process on the surface of silicalite-1 seed nanocrystals, embedded in the gel matrix, without the formation of new nuclei either on the surface of growing seed crystals or in the gel matrix. The critical processes happened during crystallization have also been characterized by different methods and evaluated by population balance modeling approach.

zeolite ZSM-5 ; crystallization ; modeling ; controllable synthesis ; mechanism

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