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 language | English |
|---|---|
| Pages (from-to) | 50-59 |
| Number of pages | 10 |
| Journal | Journal of Catalysis |
| Volume | 224 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - May 15 2004 |
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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 journal › Article
}
TY - JOUR
T1 - Observation of a compensation relation for monomolecular alkane cracking by zeolites
T2 - The dominant role of reactant sorption
AU - Van Bokhoven, Jeroen A.
AU - Williams, Bryce A.
AU - Ji, W.
AU - Koningsberger, Diek C.
AU - Kung, Harold H
AU - Miller, Jeffrey T.
PY - 2004/5/15
Y1 - 2004/5/15
N2 - 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
AB - 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
KW - Compensation effect
KW - Constable plot
KW - Hexane cracking
KW - Monomolecular cracking
KW - Mordenite
KW - Y
KW - Zeolite acidity
KW - ZSM-5
UR - http://www.scopus.com/inward/record.url?scp=1942500393&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=1942500393&partnerID=8YFLogxK
U2 - 10.1016/j.jcat.2004.02.003
DO - 10.1016/j.jcat.2004.02.003
M3 - Article
AN - SCOPUS:1942500393
VL - 224
SP - 50
EP - 59
JO - Journal of Catalysis
JF - Journal of Catalysis
SN - 0021-9517
IS - 1
ER -