Precursors of the zeolite ZSM-5 imaged by Cryo-TEM and analyzed by SAXS

Oren Regev, Yachin Cohen, Ephraim Kehat, Yeshayahu Talmon

Research output: Contribution to journalArticlepeer-review

76 Scopus citations

Abstract

The microstructural evolution in the nucleation stage of a synthesis reaction of ZSM-5 zeolite was studied, with particular emphasis on the role of the organic cation, TPA+ (tetrapropylammonium). Direct observation of the microstructure was achieved by cryo-transmission electron microscopy (cryo-TEM). The quantitative evaluation of the structural units was obtained by small-angle X-ray scattering (SAXS) measurements. In the presence of the organic cation TPA+, we found globular structural units 5 nm in diameter that aggregate to elongated bodies 44 nm long. The globular structural units were found in reaction mixtures with or without the organic template TPA-OH, as long as the pH of the initial solution was kept above 11.6. Without TPA+, aggregation to cylindrical particles was not observed after 2 h of heating, and no ZSM-5 crystallinity was attained at the end of the reaction (after 8 d). These results suggest that the zeolite ZSM-5 building blocks are globular structural units, 5 nm in diameter, containing silica, alumina, organic cation, and water, which fuse together to produce elongated aggregates that may compose the final unit cell. It is concluded that the globular structural unit is a cluster of tetrapods similar to those found in the final ZSM-5 crystals.

Original languageEnglish
Pages (from-to)314-319
Number of pages6
JournalZeolites
Volume14
Issue number5
DOIs
StatePublished - 1 Jan 1994
Externally publishedYes

Keywords

  • ZSM-5
  • Zeolite
  • cluster
  • electron microscopy
  • nucleation
  • precursor
  • small-angle X-ray scattering
  • tetrapod

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