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. doi:10.1021/j100068a027. 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.
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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. | ||||||
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Issue or Number: | 17 | ||||||
DOI: | 10.1021/j100068a027 | ||||||
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: | 15 Nov 2021 20:41 |
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