A density functional theory study of the effects of metal cations on the Brønsted acidity of H-ZSM-5

Nick O. Gonzales, Arup K. Chakraborty, Alexis T. Bell

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51 Scopus citations

Abstract

Density functional theory calculations have been carried out to establish the influence of mono- and polyvalent cations on the - Brønsted acidity of H-ZSM-5. The zeolite was modeled as a cluster containing 41-45 atoms, in the center of which is an Al(1)(OH)SiOAl(2)(OM) unit, where M+ = H+, Li+,Na+, K+,Ca(OH), A1O, A1(OH)+2. The local geometry of the Brønsted acid site is affected by the nature of M+ and this in turn causes a change in the value of the proton affinity (PA) for the site. The highest value of PA is 330 kcal/mol for M+ = H+ and the lowest value of PA is 305 kcal/rnol for M+ = AlO+. No correlation was found between the value of PA and the Mulliken charge on Al(1). With the exception of the case where M+ = A1O+, the binding energy of CO with the Brønsted acid proton is approximately 8.8 kcal/mol, independent of the nature of M+. When M+ = A1O+, the binding energy for CO is 11.1 kcal/mol. The present calculations suggest that different factors affect proton affinity and the binding energy for CO adsorption.

Original languageEnglish
Pages (from-to)135-139
Number of pages5
JournalCatalysis Letters
Volume50
Issue number3-4
DOIs
StatePublished - 1998
Externally publishedYes

Keywords

  • Brønsted acidity
  • Density functional theory
  • Zeolites

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