Journal article
Adsorption Thermodynamics and Intrinsic Activation Parameters for Monomolecular Cracking of n-Alkanes on Bronsted Acid Sites in Zeolites
Journal of physical chemistry. C, Vol.119(19), pp.10427-10438
05/14/2015
DOI: 10.1021/acs.jpcc.5b01715
Abstract
Experimental' measurements of the rate coefficient (k(app)) and apparent enthalpies and entropies of activation (Delta H-app arid Delta S-app) for alkane cracking catalyzed by acidic zeolites can be used to characterize the effects of zeolite structure and alkane size On the intrinsic enthalpy and entropy of activation, Delta H-int(double dagger) and Delta S-int(double dagger). To determine Delta H-int(double dagger) and Delta S-int(double dagger), enthalpies and entropies of adsorption, Delta Hads-H+ and Delta Sads-H+, must be determined for alkane molecules moving from the gas phase to Bronsted add sites at reaction temperatures (>673 K). Experimental values of Delta H-app and Delta S-app must also be properly defined in terms of Delta Hads-H+ and Delta Hads-H+. We report here a method for determining Delta Hads-H+ and Delta Sads-H+ in which the adsorption site is represented by a fixed volume that includes the proton. Values of Delta Hads-H+ and Delta Sads-H+ obtained from Monte Carlo simulations are in good agreement with values obtained from experimental data measured at 300-400 K. An important feature of the simulations, however, is their ability to account for the redistribution of alkane adsorbed at protons in different locations with ineteasing temperature. Values of Delta H-int(double dagger) and Delta S-int(double dagger), for the cracking of propane through n-hexane, determined from measured values of k(app) and Delta H-app and simulated: values of Delta Hads-H+ and Delta Sads-H+, agree well with values obtained independently from quantum mechanics/molecular mechanics calculations. Application of our method of analysis reveals that the observed increase in kapp with increasing n-alkane size is due primarily to a decrease in Delta H-int(double dagger) with increasing chain length and that Delta S-int(double dagger) is independent of chain length.
Details
- Title: Subtitle
- Adsorption Thermodynamics and Intrinsic Activation Parameters for Monomolecular Cracking of n-Alkanes on Bronsted Acid Sites in Zeolites
- Creators
- Amber Janda - Univ Calif Berkeley, Dept Chem & Biomol Engn, Berkeley, CA 94720 USABess Vlaisavljevich - Univ Calif Berkeley, Dept Chem & Biomol Engn, Berkeley, CA 94720 USALi-Chiang Lin - Univ Calif Berkeley, Dept Chem & Biomol Engn, Berkeley, CA 94720 USAShaama Mallikarjun Sharada - Univ Calif Berkeley, Dept Chem & Biomol Engn, Berkeley, CA 94720 USABerend Smit - École Polytechnique Fédérale de LausanneMartin Head-Gordon - Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USAAlexis T. Bell - Univ Calif Berkeley, Dept Chem & Biomol Engn, Berkeley, CA 94720 USA
- Resource Type
- Journal article
- Publication Details
- Journal of physical chemistry. C, Vol.119(19), pp.10427-10438
- DOI
- 10.1021/acs.jpcc.5b01715
- ISSN
- 1932-7447
- eISSN
- 1932-7455
- Publisher
- Amer Chemical Soc
- Number of pages
- 12
- Grant note
- Chevron Energy Technology Co. DE-SC0001015 / Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences; United States Department of Energy (DOE) American Society for Engineering Education DE-AC02-05CH11231 / Office of Science of the U.S. Department of Energy; United States Department of Energy (DOE) Center for Gas Separations Relevant to Clean Energy Technologies NDSEG fellowship
- Language
- English
- Date published
- 05/14/2015
- Academic Unit
- Chemistry
- Record Identifier
- 9984618517902771
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