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Mechanism of Structure Direction in the Synthesis of Si-ZSM-5: An Investigation by Intermolecular ^1H-^(29)Si CP MAS NMR

Burkett, Sandra L. and Davis, Mark E. (1994) Mechanism of Structure Direction in the Synthesis of Si-ZSM-5: An Investigation by Intermolecular ^1H-^(29)Si CP MAS NMR. Journal of Physical Chemistry, 98 (17). pp. 4647-4653. ISSN 0022-3654. https://resolver.caltech.edu/CaltechAUTHORS:20180529-155836771

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Abstract

The role of tetrapropylammonium (TPA) ions as a structure-directing agent in the synthesis of pure-silica ZSM-5 (Si-ZSM-5) is investigated by solid-state NMR. It has previously been proposed that the mechanism of structure direction involves preorganization of silicate species around the TPA ions with subsequent assembly of these inorganic-organic composite structures to yield crystalline Si-ZSM-5 with occluded TPA molecules. However, such structures have not been directly observed. Here, ^1H-^(29)Si CP MAS NMR is performed between the protons of TPA and the silicon atoms of the zeolite framework precursors in a deuterated synthesis medium to probe the relationship between the organic and inorganic components. The ^1H-^(29)Si CP MAS NMR results indicate that short-range intermolecular interactions, i.e., on the order of van der Waals interactions (≈3.3 Å for H to Si), are established during the heating of the zeolite synthesis gel prior to the development of long-range order indicative of the ZSM-5 structure. ^1H-^(13)C CP MAS NMR spectra suggest that the TPA molecules within the composite inorganic-organic structures adopt a conformation similar to that which they have in the zeolite product. These results thus provide the first direct evidence for the existence of preorganized inorganic-organic composite structures during the synthesis of Si-ZSM-5. They also demonstrate the types of noncovalent intermolecular interactions that are relevant to the existence of an organic structure-directing effect. A modified mechanism of structure direction and crystal growth of Si-ZSM-5 is proposed.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://dx.doi.org/10.1021/j100068a027DOIArticle
ORCID:
AuthorORCID
Davis, Mark E.0000-0001-8294-1477
Alternate Title:Mechanism of Structure Direction in the Synthesis of Si-ZSM-5: An Investigation by Intermolecular 1H-29Si CP MAS NMR
Additional Information:© 1994 American Chemical Society. Received: November 4, 1993; In Final Form: January 12, 1994. Financial support has been provided by the Chevron Research and Technology Co.
Funders:
Funding AgencyGrant Number
Chevron Research and Technology Co.UNSPECIFIED
Issue or Number:17
Record Number:CaltechAUTHORS:20180529-155836771
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180529-155836771
Official Citation:Mechanism of Structure Direction in the Synthesis of Si-ZSM-5: An Investigation by Intermolecular 1H-29Si CP MAS NMR Sandra L. Burkett and Mark E. Davis The Journal of Physical Chemistry 1994 98 (17), 4647-4653 DOI: 10.1021/j100068a027
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86690
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:29 May 2018 23:26
Last Modified:09 Mar 2020 13:18

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