Nature and catalytic role of extraframework aluminum in faujasite zeolite : a theoretical perspective

C. Liu, G. Li, E.J.M. Hensen, E.A. Pidko

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

A comprehensive periodic DFT study complemented by ab initio thermodynamic analysis was carried out to determine the speciation of extraframework aluminium (EFAl) in faujasite zeolite. The structure and stability of a wide range of mono- bi-, tri- and tetranuclear EFAl complexes stabilized at different locations in faujasite were investigated. The thermodynamic cycles connecting these complexes were constructed involving such elementary steps as hydration/dehydration, proton transfer, and condensation reactions. Using ab initio thermodynamics analysis it was predicted that during high-temperature zeolite activation, the EFAl species self-organize into cationic clusters with more than one Al center. The resulting tri- and tetranuclear clusters are preferentially stabilized inside the small sodalite cages of faujasite that provide a favorable coordination and charge-compensation environment for the large multiply charged cationic clusters. The presence of such cationic EFAl clusters inside the inaccessible sodalite cages strongly enhances the protolytic propane cracking activity of vicinal supercage Brønsted acid sites.
Original languageEnglish
Pages (from-to)7024-7033
Number of pages10
JournalACS Catalysis
Volume5
Issue number11
DOIs
Publication statusPublished - Nov 2015

Keywords

  • extraframework aluminum
  • faujasite
  • acid catalysis
  • DFT
  • ab initio thermodynamic analysis
  • alkane cracking

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