Entropy considerations in monomolecular cracking of alkanes on acidic zeolites

Aditya Bhan, Rajamani Gounder, Josef Macht, Enrique Iglesia

Research output: Contribution to journalArticlepeer-review

83 Scopus citations

Abstract

Compensation between adsorption entropies and enthalpies results in less than a two-fold variation in adsorption equilibrium constants for C3-C6 alkanes at temperatures relevant for monomolecular cracking; the size-independent activation energy for C{single bond}C bond activation in C3-C6 alkanes indicates that the marked increase in monomolecular cracking turnover rates observed with alkane chain size reflects a concurrent increase in activation entropies. Thermodynamic treatments for non-ideal systems rigorously describe confinement effects within zeolite channels and show that pre-exponential factors depend on solvation effects of the zeolite-host environment through variations in the thermodynamic activity of the zeolitic proton. Observed differences in rates and selectivities of monomolecular alkane activation with zeolite structure, after normalization to intrazeolitic concentrations, reflect differences in intrinsic rate constants.

Original languageEnglish (US)
Pages (from-to)221-224
Number of pages4
JournalJournal of Catalysis
Volume253
Issue number1
DOIs
StatePublished - Jan 1 2008
Externally publishedYes

Bibliographical note

Funding Information:
The authors acknowledge Chevron Energy Technology Company for financial support.

Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.

Keywords

  • Compensation effect
  • Confinement effects
  • Enthalpy
  • Entropy
  • Intrazeolitic concentration
  • Monomolecular alkane activation

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