Synthesis of silicalite-1 using a disiloxane-based structure-directing agent

Hirotaka Ishii, Keiji Itabashi, Tatsuya Okubo, Atsushi Shimojima

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

A cationic organosiloxane compound where two tetrapropylammonium (TPA) cations are bridged by a tetramethyldisiloxane unit (MSi-TPA) has been used as a structure-directing agent (SDA) for the synthesis of a pure silica MFI-type zeolite, silicalite-1, with a unique microstructure and particle morphology. The hydrothermal treatment of the mixture of tetraethoxysilane as a silica source, MSi-TPAOH, and water yields solid products that are identified as silicalite-1 by X-ray diffraction and solid-state 29Si MAS NMR. Solid-state 29Si and 13C CP/MAS NMR and elemental analyses confirm that MSi-TPA is covalently incorporated in the MFI framework via cleavage of the disiloxane linkage. Compared with conventional silicalite-1 prepared with TPA cations, the amount of defect sites is higher, which can be attributed to the attachment of the organosilyl groups to the framework by Si-O-Si bonds. Scanning electron microscopic (SEM) observation shows spherical particle morphology that is quite different from the typical coffin-shaped crystals obtained with TPA. Importantly, MFI is not formed when triethoxysilyl- and diethoxysilyl-TPAs, instead of MSi-TPA, are used as SDAs under similar conditions, suggesting that the possible number of Si-O-Si linkages formed by SDAs greatly affects the crystallization process of MFI zeolite.

Original languageEnglish
Pages (from-to)158-163
Number of pages6
JournalMicroporous and Mesoporous Materials
Volume139
Issue number1-3
DOIs
Publication statusPublished - 2011 Mar 1
Externally publishedYes

Keywords

  • MFI-type zeolite
  • Organosiloxanes
  • Slicalite-1
  • Structure-directing agent

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials

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