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Synthesis of Hydrophobic Molecular Sieves by Hydrothermal Treatment with Acetic Acid

Jones, Christopher W. and Hwang, Son-Jong and Okubo, Tatsuya and Davis, Mark E. (2001) Synthesis of Hydrophobic Molecular Sieves by Hydrothermal Treatment with Acetic Acid. Chemistry of Materials, 13 (3). pp. 1041-1050. ISSN 0897-4756. doi:10.1021/cm0007961.

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A series of calcined borosilicate molecular sieves are treated hydrothermally with aqueous acetic acid and subsequently characterized in detail. The acid treatments are shown to expel boron from the molecular sieves, and the defects created by the boron removal are subsequently healed with silicon dissolved from other parts of the crystal. By use of this procedure, highly crystalline, hydrophobic all-silica CIT-1 and SSZ-33 (CON topology) molecular sieves are synthesized for the first time. ^(29)Si Bloch decay (BD) and cross-polarization magic-angle spinning (CPMAS) NMR spectra indicate that the materials have few internal defects and allow for structural characterization of CON materials by 29Si MAS NMR. Seven unique tetrahedral silicon species are identified in the spectra in agreement with the published crystal structure. The effects of treatment conditions such as acid type, solution pH, and temperature are studied in detail. Conditions near the isoelectric point of silica (pH = 0−2) are found to be efficient for the production of a variety of hydrophobic materials with few structural defects including molecular sieves of the *BEA, CON, and MWW topologies. Detailed control studies using SSZ-33 show that the nearly defect-free materials contain triangular mesopores that are clearly distinguishable in field-emission electron microscopy images. The silica that previously inhabited the mesopores is a likely source for the species required to heal the defects created by boron expulsion. In addition to healing the vacancies previously inhabited by boron with dissolved silicon, an additional aluminum or gallium source can be added to the acetic acid solution and the ions are incorporated into the framework. Many of the defects that are not filled with the Al^(3+) or Ga^(3+) species are filled with silicon during the treatment to produce a more hydrophobic metallosilicate than the one containing internal silanol defects.

Item Type:Article
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URLURL TypeDescription ItemSupporting Information
Hwang, Son-Jong0000-0002-3210-466X
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 2001 American Chemical Society. Received 4 October 2000. Published online 23 January 2001. Published in print 1 March 2001. This work was partially supported by Chevron. C.W.J. thanks Akzo Nobel and BP Amoco for additional financial support.
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Issue or Number:3
Record Number:CaltechAUTHORS:20170201-101506437
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Official Citation:Synthesis of Hydrophobic Molecular Sieves by Hydrothermal Treatment with Acetic Acid Christopher W. Jones, Son-Jong Hwang, Tatsuya Okubo, and Mark E. Davis Chemistry of Materials 2001 13 (3), 1041-1050 DOI: 10.1021/cm0007961
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73925
Deposited By: Ruth Sustaita
Deposited On:01 Feb 2017 19:04
Last Modified:11 Nov 2021 05:23

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