Zeolites are microporous crystalline materials with pores and channels in molecular dimensions, high hydrothermal stability, high surface area, and shape selectivity, which have been utilized in various industrial applications as catalysts, adsorbents and ion-exchangers. Organic molecules can play an important role in zeolite synthesis as pore filling agents, structure-directing agents or true templates.1 Conventionally, industrially important zeolites such as MFI, MEL and CHA-type zeolites have been synthesized by using tetrapropylammonium cation (TPA), tetrabutylammonium cation (TBA) and N,N,N-trimethyl-1-adamantammonium cation (TMAda) as organic structure-directing agents (OSDAs), respectively. Interestingly, dimerization of conventional OSDA can provide for a simple synthetic route for novel OSDAs yielding zeolites with unique features. For example, formation of hierarchically, sequentially intergrown MFI zeolite was achieved by TPA dimer (N,N,N,N’,N’,N’-hexapropylpentanediammonium cation) as an OSDA without using any mesoporogens.2
In this research, we aim to employ OSDAs prepared by dimerization of conventional organic cations in zeolite synthesis. Specifically, the effects of alkyl chain length in the dimerized OSDAs and synthesis gel composition to the phase selectivity and morphology of resulting zeolite were systematically investigated. The obtained products were characterized by several techniques including X-ray diffraction, field emission scanning electron microscopy and nitrogen adsorption. The results suggested that the selectivity and morphology of the products are greatly influenced by the alkyl chain length of dimerized OSDAs and synthesis gel composition employed.
1. M. E. Davis and R. F. Lobo, Chem. Mater., 4, 1992, 756-768.
2. W. Chaikittisilp, Y. Suzuki, R. R. Mukti, T. Suzuki, K. Sugita, K. Itabashi, A. Shimojima, T. Okubo, Angew. Chem. Int. Ed., 52, 2013, 3439-3443.
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