Observation of a compensation relation for monomolecular alkane cracking by zeolites: The dominant role of reactant sorption

Jeroen A. Van Bokhoven, Bryce A. Williams, W. Ji, Diek C. Koningsberger, Harold H Kung, Jeffrey T. Miller

Research output: Contribution to journalArticle

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Abstract

Monomolecular cracking of alkanes was investigated over zeolites of different structure types and after different treatments. Large deviations in apparent rates of reaction and apparent kinetic parameters were detected for zeolites of different structure types; smaller changes were observed within a structure type. The Si/Al ratio and different crystal sizes had no effect on turnover frequency; however, steaming of mordenite and ZSM-5 enhances the rate of reaction by a factor of 2-5 due to the formation of Lewis acid sites with enhanced heat of adsorption, although the number of Brønsted sites decreased. The apparent activation energies and preexponential factors showed a linear compensation relation in a Constable plot. Using the Langmuir-Hinshelwood kinetics formalism, the apparent kinetic parameters include enthalpy and entropy of adsorption and surface reaction terms. If the enthalpy and entropy of adsorption are linearly related, which is experimentally observed for unsteamed and steamed mordenite, then the apparent compensation effect implies that the observed differences in rate are dominated by differences in adsorption of the reactant in the pores of the zeolites, rather than by differences in acid strength. Zeolites with smaller pores show enhanced adsorption, and consequently the rate of reaction increases in the order H-Y

Original languageEnglish
Pages (from-to)50-59
Number of pages10
JournalJournal of Catalysis
Volume224
Issue number1
DOIs
Publication statusPublished - May 15 2004

Fingerprint

Zeolites
Alkanes
zeolites
Paraffins
sorption
alkanes
Sorption
Adsorption
adsorption
Kinetic parameters
Enthalpy
kinetics
Entropy
enthalpy
entropy
porosity
Lewis Acids
acids
Acids
Surface reactions

Keywords

  • Compensation effect
  • Constable plot
  • Hexane cracking
  • Monomolecular cracking
  • Mordenite
  • Y
  • Zeolite acidity
  • ZSM-5

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

Observation of a compensation relation for monomolecular alkane cracking by zeolites : The dominant role of reactant sorption. / Van Bokhoven, Jeroen A.; Williams, Bryce A.; Ji, W.; Koningsberger, Diek C.; Kung, Harold H; Miller, Jeffrey T.

In: Journal of Catalysis, Vol. 224, No. 1, 15.05.2004, p. 50-59.

Research output: Contribution to journalArticle

Van Bokhoven, Jeroen A. ; Williams, Bryce A. ; Ji, W. ; Koningsberger, Diek C. ; Kung, Harold H ; Miller, Jeffrey T. / Observation of a compensation relation for monomolecular alkane cracking by zeolites : The dominant role of reactant sorption. In: Journal of Catalysis. 2004 ; Vol. 224, No. 1. pp. 50-59.
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