Cyclic diquaternary ammoniums for nanocrystalline BEA, MTW and MFI zeolites with intercrystalline mesoporosity

Abstract

3,10-Diazoniabicyclo[10.2.2]hexadeca-12,14,15-triene-3,3,10,10-tetramethyl-dichloride is an effective structure-directing agent for BEA zeolite under a high concentration of Na⁺. The pseudomorphic crystallization process led to nanocrystalline BEA particles possessing a large volume of intercrystalline mesopores. The synthesis of nanocrystalline zeolite has been extended to other cyclic diammonium compounds that can generate BEA, MTW and MFI zeolite structures. Phase diagrams for these nanocrystalline zeolites have been constructed using sodium silicate as a silica source. The nanocrystalline morphologies and intercrystalline mesoporosity have been characterized by electron microscopy and N₂ adsorption. The result indicates that the pseudomorphic crystallization process is limited to BEA, and not MTW or MFI despite their nanocrystalline morphologies.