Cooperative structure-directing effect of fluorine-containing organic molecules and fluoride anions in the synthesis of zeolites

M Arranz, J Perez-Pariente, P A Wright, A M Z Slawin, T Blasco, L Gomez-Hortiguela, F Cora

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)

Abstract

Dibenzyldimethylammonium (DBDM) cations, singly fluorinated at the ortho, meta, and para positions of the aromatic ring, have been investigated as structure-directing agents (SDAs) for the synthesis of all-silica zeolites in fluoride media and compared with the nonfluorinated molecule. The nonfluorinated DBDM cation can direct the synthesis either to an all-silica zeolite beta or to an all-silica zeolite ZSM-50 with the EUO framework topology. Under the same conditions that DBDM gives zeolite beta, benzyl-orthofluorobenzyldimethylammonium (o-FDBDM) readily directs the crystallization of pure all-silica ZSM-50 [Cmma, a = 13.726(3) angstrom, b = 22.171(5) angstrom, c = 20.254(4) angstrom]. Replacing o-FDBDM by the para fluoro derivative (p-FDBDM) results in a much slower crystallization of ZSM-50 whereas no crystalline product results if the meta fluoro derivative (m-FDBDM) is added. Single-crystal diffraction studies of selected ZSM-50 crystals prepared using DBDM and o-FDBDM determine the location of the template and of charge-balancing fluoride atoms bound to framework silicon atoms and included within [41516 2] cages in the framework. Furthermore, the o-FDBDM is found to order within the structure, with the fluorine-containing aromatic rings occupying channel, rather than cavity, locations. Computer simulations indicate how the position of fluorine in the SDA influences the template ordering.

Original languageEnglish
Pages (from-to)4374-4385
Number of pages12
JournalChemistry of Materials
Volume17
DOIs
Publication statusPublished - 23 Aug 2005

Keywords

  • SILICA ZEOLITES
  • TEMPLATES
  • AGENTS
  • SIEVES
  • EU-1

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