| Crystallization behavior of zeolite MCM-22 synthesized by a vapor-phase transport method (VPT) has been studied. The aluminosilicate gel precursors and the products were characterized by powder XRD and SEM, etc. Based on the experimental results, the crystallization mechanism of VPT method has been discussed and an integration of the synthesis and molding of catalyst was proposed, which would lead to the preparation of an integrated monolistic zeolite catalyst.This study indicated that a pure zeolite MCM-22 could be obtained from different silica sources, including a silicic acid, a colloidal silica as well as a sodium silicate. Using silicic acid as the silica source, it was found that the preparation temperature of the gel precursors played a key role on its structure and the subsequent crystallization process. For sodium silicate, the value of pH had a significant effect on the structure of the sol-gels and gelatification, and there was no gel precursors obtained in strong acid or alkaline medium. The optimum content of Na+ for the synthesis is much lower than that in the traditional hydrothermal synthetic methods, which simplifies the washing process. And decreasing the amount of water and HMI simultaneously tends to yield other phase products, but their presence is necessary for the crystallization.The crystallization of dry gel after tabletting occurred both on the surface and inside. It seems that the crystals could grow up perfectly because of the existence of many secondary voids and appeared in the form of round, thin and interpenetrating platelets (or sheets) with a size of 4μm. Almost all these crystals were vertically oriented on the surface. We proposed that the VPT crystallization process follows the liquid-phase transformation mechanism. Once nuclei are formed, the higher growth rate in the layer direction results in the growth of MCM-22 crystals, and the dissolution of silica source is the controlling step for the crystallization.
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