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Adsorption of C2-C8 n-alkanes in zeolites

Bart De Moor UGent, Marie-Françoise Reyniers UGent, Oliver C Gobin, Johannes A Lercher and Guy Marin UGent (2011) JOURNAL OF PHYSICAL CHEMISTRY C. 115(4). p.1204-1219
abstract
Adsorption of n-alkanes has been studied in the industrially relevant zeolites H-FAU, H-BEA, H-MOR, and H-ZSM-5 combining QM-Pot(MP2//B3LYP) with statistical thermodynamics calculations and assuming a mobile adsorbate. In H-ZSM-5, adsorption at the intersection site with the hydrocarbon chain extending in the straight channel (SC+I) as well as in the zigzag channel (ZC+I) has been studied. In addition, differential heats of adsorption and adsorption isotherms at temperatures from 301 to 400 K of all C3-C6 n-alkane in H-ZSM-5 have been measured simultaneously via calorimetry and gravimetry. Calculated adsorption enthalpies are independent of temperature and are virtually identical to the adsorption energies. The adsorption strength increases in the order H-FAU < H-BEA < H-MOR < H-ZSM-5 (SC+I) < H-ZSM-5 (ZC+I) and varies linearly with the carbon number. As compared to experimental values, the calculated adsorption strength is overestimated by some 2 kJ mol(-1)/CH2 in FAU up to some 4 kJ mol(-1)/CH2 in H-ZSM-5 suggesting that the QM-Pot(MP2//B3LYP) calculations overestimate van der Waals stabilizing interactions and a correction term has been proposed. Adsorption entropy losses are independent of temperature and increase in the order H-FAU < H-BEA < H-MOR < H-ZSM-5 (SC+I) < H-ZSM-5 (ZC+I), according to the pore size of the zeolites. The calculated adsorption entropies agree nicely with available experimental results in all zeolites. QM-Pot(MP2//B3LYP) calculated adsorption equilibrium coefficients (using the corrected adsorption enthalpies) correspond relatively well to experimentally determined values. Comparison of relative turnover frequencies with relative adsorption equilibrium coefficients indicates that the variation of the equilibrium coefficient with the carbon number or with the zeolite can only partly explain the observed reactivity differences in monomolecular cracking of n-alkanes. In agreement with experimental observations, our results indicate that the difference in reactivity of the n-alkanes for monomolecular cracking in a given zeolite mainly originates from a difference in intrinsic monomolecular cracking rate coefficients.
Please use this url to cite or link to this publication:
author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
COMPENSATION RELATION, LINEAR HYDROCARBONS, FAUJASITE ZEOLITES, QUANTUM-MECHANICS, CATALYTIC-ACTIVITY, BRONSTED ACID SITES, EXTENDED SYSTEMS, MONOMOLECULAR CRACKING, AB-INITIO, LIGHT ALKANES
journal title
JOURNAL OF PHYSICAL CHEMISTRY C
J. Phys. Chem. C
volume
115
issue
4
pages
1204 - 1219
Web of Science type
Article
Web of Science id
000286639400044
JCR category
MATERIALS SCIENCE, MULTIDISCIPLINARY
JCR impact factor
4.805 (2011)
JCR rank
23/229 (2011)
JCR quartile
1 (2011)
ISSN
1932-7447
DOI
10.1021/jp106536m
project
HPC-UGent: the central High Performance Computing infrastructure of Ghent University
language
English
UGent publication?
yes
classification
A1
copyright statement
I have transferred the copyright for this publication to the publisher
id
1220586
handle
http://hdl.handle.net/1854/LU-1220586
date created
2011-05-10 11:38:11
date last changed
2013-09-17 10:47:41
@article{1220586,
  abstract     = {Adsorption of n-alkanes has been studied in the industrially relevant zeolites H-FAU, H-BEA, H-MOR, and H-ZSM-5 combining QM-Pot(MP2//B3LYP) with statistical thermodynamics calculations and assuming a mobile adsorbate. In H-ZSM-5, adsorption at the intersection site with the hydrocarbon chain extending in the straight channel (SC+I) as well as in the zigzag channel (ZC+I) has been studied. In addition, differential heats of adsorption and adsorption isotherms at temperatures from 301 to 400 K of all C3-C6 n-alkane in H-ZSM-5 have been measured simultaneously via calorimetry and gravimetry. Calculated adsorption enthalpies are independent of temperature and are virtually identical to the adsorption energies. The adsorption strength increases in the order H-FAU {\textlangle} H-BEA {\textlangle} H-MOR {\textlangle} H-ZSM-5 (SC+I) {\textlangle} H-ZSM-5 (ZC+I) and varies linearly with the carbon number. As compared to experimental values, the calculated adsorption strength is overestimated by some 2 kJ mol(-1)/CH2 in FAU up to some 4 kJ mol(-1)/CH2 in H-ZSM-5 suggesting that the QM-Pot(MP2//B3LYP) calculations overestimate van der Waals stabilizing interactions and a correction term has been proposed. Adsorption entropy losses are independent of temperature and increase in the order H-FAU {\textlangle} H-BEA {\textlangle} H-MOR {\textlangle} H-ZSM-5 (SC+I) {\textlangle} H-ZSM-5 (ZC+I), according to the pore size of the zeolites. The calculated adsorption entropies agree nicely with available experimental results in all zeolites. QM-Pot(MP2//B3LYP) calculated adsorption equilibrium coefficients (using the corrected adsorption enthalpies) correspond relatively well to experimentally determined values. Comparison of relative turnover frequencies with relative adsorption equilibrium coefficients indicates that the variation of the equilibrium coefficient with the carbon number or with the zeolite can only partly explain the observed reactivity differences in monomolecular cracking of n-alkanes. In agreement with experimental observations, our results indicate that the difference in reactivity of the n-alkanes for monomolecular cracking in a given zeolite mainly originates from a difference in intrinsic monomolecular cracking rate coefficients.},
  author       = {De Moor, Bart and Reyniers, Marie-Fran\c{c}oise and Gobin, Oliver C and Lercher, Johannes A and Marin, Guy},
  issn         = {1932-7447},
  journal      = {JOURNAL OF PHYSICAL CHEMISTRY C},
  keyword      = {COMPENSATION RELATION,LINEAR HYDROCARBONS,FAUJASITE ZEOLITES,QUANTUM-MECHANICS,CATALYTIC-ACTIVITY,BRONSTED ACID SITES,EXTENDED SYSTEMS,MONOMOLECULAR CRACKING,AB-INITIO,LIGHT ALKANES},
  language     = {eng},
  number       = {4},
  pages        = {1204--1219},
  title        = {Adsorption of C2-C8 n-alkanes in zeolites},
  url          = {http://dx.doi.org/10.1021/jp106536m},
  volume       = {115},
  year         = {2011},
}

Chicago
De Moor, Bart, Marie-Françoise Reyniers, Oliver C Gobin, Johannes A Lercher, and Guy Marin. 2011. “Adsorption of C2-C8 N-alkanes in Zeolites.” Journal of Physical Chemistry C 115 (4): 1204–1219.
APA
De Moor, Bart, Reyniers, M.-F., Gobin, O. C., Lercher, J. A., & Marin, G. (2011). Adsorption of C2-C8 n-alkanes in zeolites. JOURNAL OF PHYSICAL CHEMISTRY C, 115(4), 1204–1219.
Vancouver
1.
De Moor B, Reyniers M-F, Gobin OC, Lercher JA, Marin G. Adsorption of C2-C8 n-alkanes in zeolites. JOURNAL OF PHYSICAL CHEMISTRY C. 2011;115(4):1204–19.
MLA
De Moor, Bart, Marie-Françoise Reyniers, Oliver C Gobin, et al. “Adsorption of C2-C8 N-alkanes in Zeolites.” JOURNAL OF PHYSICAL CHEMISTRY C 115.4 (2011): 1204–1219. Print.