Spectral editing: A quantitative application of spin-echo nuclear magnetic resonance spectroscopy to the study of 27Al in zeolite catalysts

Kirk D. Schmitt, Jürgen Haase, Eric Oldfield

Research output: Contribution to journalArticlepeer-review

Abstract

27Al spin-echo nuclear magnetic resonance (n.m.r.) is used to measure the spin-spin relaxation times, T2H, for a substantial number of model compounds, and a theory (with no adjustable parameters) based on AIAI dipolar interactions combined with crystallographically determined AIAI distances is used to estimate T2H. The homonuclear magnetic dipole interaction explains the experimental data reasonably well for compounds with high Al levels, but much less well for compounds with low levels of AI, where structure-specific interactions are important. Such structure-specific interactions are exploited to edit zeolitic AI from the background binder in alumina-bound ZSM-5 and in dealuminated zeolite-Y catalysts containing nonframework (NFW) AI. Editing allows quantitative analysis of the zeolitic components. For dealuminated zeolite Y, it is concluded that peaks assigned by others to "pentacoordinate" AI may actually arise from NFW aluminum, based on the fact that their T2H is short relative to framework (FW) AI. Theory and experimental results for the technically more demanding measurement of T2H under conditions of "magic-angle" sample spinning (MAS) with synchronous sampling are also reported. Spin-echo editing of synchronously sampled 27AI MAS n.m.r. spectra are shown to be useful for determining the FW zeolitic AI content of realistically formulated (kaolinite bound) and steamed/calcined fluidized bed cracking (FCC) catalysts. The loss of framework AI in two series of steamed FCC catalysts is less precipitous than the loss in catalytic activity, as measured by the hexane cracking α parameter.

Original languageEnglish (US)
Pages (from-to)89-100
Number of pages12
JournalZeolites
Volume14
Issue number2
DOIs
StatePublished - Feb 1994

Keywords

  • Spin-echo editing
  • alumina bound catalysts
  • aluminum n.m.r.
  • kaolinite theory
  • steam cracking

ASJC Scopus subject areas

  • Environmental Science(all)

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