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Entropy of Pure-Silica Molecular Sieves

Piccione, Patrick M. and Woodfield, Brian F. and Boerio-Goates, Juliana and Navrotsky, Alexandra and Davis, Mark E. (2001) Entropy of Pure-Silica Molecular Sieves. Journal of Physical Chemistry B, 105 (25). pp. 6025-6030. ISSN 1520-6106. doi:10.1021/jp010491p.

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The entropies of a series of pure-silica molecular sieves (structural codes ^*BEA, FAU, MFI, and MTT) are obtained by calorimetric measurements of low-temperature heat capacity. The third-law entropies at 298.15 K are (on the basis of 1 mol of SiO_2):  ^*BEA, 44.91 ± 0.11 J·K^(-1)·mol^(-1); FAU, 44.73 ± 0.11 J·K^(-1)·mol^(-1); MFI, 45.05 ± 0.11 J·K^(-1)·mol^(-1); MTT, 45.69 ± 0.11 J·K^(-1)·mol^(-1); while the corresponding entropies of transition from quartz at 298.15 K are ^*BEA, 3.4 J·K^(-1)·mol^(-1); FAU, 3.2 J·K^(-1)·mol^(-1); MFI, 3.6 J·K^(-1)·mol^(-1); MTT, 4.2 J·K^(-1)·mol^(-1). The entropies span a very narrow range at 3.2−4.2 J·K^(-1)·mol^(-1) above quartz, despite a factor of 2 difference in molar volume. This confirms that there are no significant entropy barriers to transformations between SiO_2 polymorphs. Finally, the Gibbs free energy of transformation with respect to quartz is calculated for eight SiO_2 phases and all are found to be within twice the available thermal energy of each other at 298.15 K.

Item Type:Article
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Navrotsky, Alexandra0000-0002-3260-0364
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 2001 American Chemical Society. Received 7 February 2001. Published online 31 May 2001. Published in print 1 June 2001. Financial support for this work was provided by the Chevron Research and Technology Co. P.M.P. thanks Dr. Stacey Zones (Chevron) for providing the ZSM-23 (MTT) sample. J.B.G. and B.F.W. thank Rebecca Stevens and B. Hom for assistance with the heat capacity measurements and B. Lang for calculations. A.N. thanks the National Science Foundation (Grant DMR/97-31782) for support.
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Chevron Research and Technology Co.UNSPECIFIED
NSFDMR 97-31782
Issue or Number:25
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Official Citation:Entropy of Pure-Silica Molecular Sieves Patrick M. Piccione, Brian F. Woodfield, Juliana Boerio-Goates, Alexandra Navrotsky, and Mark E. Davis The Journal of Physical Chemistry B 2001 105 (25), 6025-6030 DOI: 10.1021/jp010491p
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77545
Deposited By: Ruth Sustaita
Deposited On:18 May 2017 18:47
Last Modified:15 Nov 2021 17:31

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