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Thermochemical study of the stability of frameworks in high silica zeolites

Petrovic, Ivan and Navrotsky, Alexandra and Davis, Mark E. and Zones, Stacy I. (1993) Thermochemical study of the stability of frameworks in high silica zeolites. Chemistry of Materials, 5 (12). pp. 1805-1813. ISSN 0897-4756. doi:10.1021/cm00036a019.

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The series of high-silica zeolites ZSM-5,ZSM-11,ZSM-12, SSZ-24, cubic and hexagonal faujasite has been studied to understand the relation between crystal structure and stability in open silicate frameworks. High-temperature solution calorimetry using lead borate (2PbO_2•B_2O_3) solvent at 977 K measured enthalpies of solution and transposed temperature drop calorimetry obtained heat contents at 977 K. Data have been compared with those for quartz and other “dense”, crystalline polymorphs of silica. The enthalpies of formation at 298 K are as follows: ZSM-12, -(902.0 ± 1.3); ZSM-5, -(902.5 ± 1.3); ZSM-11, (902.5 ± 1.4); SSZ-24, -(903.5 ± 1.3); hexagonal faujasite, -(900.2 ± 1.3); and cubic faujasite, -(897.1 ± 1.2) kJ/mol. The value for quartz is -(910.70 ± 1.00) kJ/mol. All zeolitic silicas are only 7-14 kJ/mol less stable in enthalpy than quartz. This implies an entropic or kinetic rather than a large stabilizing energetic role of the template in zeolite synthesis. The small variations in energy among these structures cannot be directly related either to the degree of ”openness” (framework density or molar volume) or to the mean Si-O-Si angle. Rather, the overall distribution of bond angles seems to dictate the energy of these structures, with Si-O-Si angles below 140° being the major destabilizing factor. On the other hand, heat contents, (H_(977)-H_(298), including those for “dense” crystalline polymorphs, show a linear dependence on the framework density or molar volume.

Item Type:Article
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URLURL TypeDescription
Navrotsky, Alexandra0000-0002-3260-0364
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 1993 American Chemical Society. Received May 12, 1993. Revised Manuscript Received October 4, 1993. The authors thank Dr. J. B. Higgins of Mobil Research and Development Co. for many useful discussions, especially of crystallography, and Dr. J. Cook of Tosoh USA for providing the sample of high-silica cubic faujasite. We also thank M. Borcsik from Princeton University for ICPES and AAS analyses and Dr. J. S. Delaney from Rutgers University for help with electron microprobe work. Comments from Dr. E. M. Flanigen of UOP Research and Development are also appreciated. This work was supported by the U. S. Department of Energy (Grant DE-FG 02-85ER13437).
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Department of Energy (DOE)DE-FG02-85ER13437
Issue or Number:12
Record Number:CaltechAUTHORS:20180507-141347118
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Official Citation:Thermochemical study of the stability of frameworks in high silica zeolites Ivan Petrovic, Alexandra Navrotsky, Mark E. Davis, and Stacy I. Zones Chemistry of Materials 1993 5 (12), 1805-1813 DOI: 10.1021/cm00036a019
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86262
Deposited By: George Porter
Deposited On:07 May 2018 22:23
Last Modified:15 Nov 2021 20:36

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