Synthesis of pure silica MFI zeolites using imidazolium-based long dications. A comparative study of structure-directing effects derived from a further spacer length increaseElectronic supplementary information (ESI) available: 1H NMR in D2O of the two organic dications used in this work; XRD patterns, 1H MAS NMR spectra, thermogravimetric analysis in flowing air of as-made zeolites; N2 adsorption isotherms of calcined samples; additional locations of the dications in folded conformations. See DOI: 10.1039/c8dt01127c

Synthesis of pure silica MFI zeolites using imidazolium-based long dications. A comparative study... Length-dependent structure direction of linear methylimidazolium-based dications towards MFI zeolite, previously known only for the tetramethylene spacer, has also been found for octamethylene and decamethylene spacers. This works only under highly concentrated conditions, whereas dilution always tends to favor TON, a default structure that is the only zeolite obtained with the other reported dications (with tri-, penta-, and hexamethylene spacers). The locations and conformations of the dications have been studied by molecular mechanics simulations. As longer dications introduce lower density of positive charges in the zeolite, the density of connectivity defects also decreases. Finally, these long dications cannot easily place each charged imidazolium ring in the two possible orientations (either parallel or perpendicular to 4MR close to F sites) found for the tetramethylene case. Hence, although the three MFI materials display two 19F NMR resonances at similar chemical shifts, their relative intensities strongly vary as a function of the spacer length. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Dalton Transactions Royal Society of Chemistry

Synthesis of pure silica MFI zeolites using imidazolium-based long dications. A comparative study of structure-directing effects derived from a further spacer length increaseElectronic supplementary information (ESI) available: 1H NMR in D2O of the two organic dications used in this work; XRD patterns, 1H MAS NMR spectra, thermogravimetric analysis in flowing air of as-made zeolites; N2 adsorption isotherms of calcined samples; additional locations of the dications in folded conformations. See DOI: 10.1039/c8dt01127c

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Publisher
The Royal Society of Chemistry
Copyright
This journal is © The Royal Society of Chemistry
ISSN
1477-9226
eISSN
1477-9234
D.O.I.
10.1039/c8dt01127c
Publisher site
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Abstract

Length-dependent structure direction of linear methylimidazolium-based dications towards MFI zeolite, previously known only for the tetramethylene spacer, has also been found for octamethylene and decamethylene spacers. This works only under highly concentrated conditions, whereas dilution always tends to favor TON, a default structure that is the only zeolite obtained with the other reported dications (with tri-, penta-, and hexamethylene spacers). The locations and conformations of the dications have been studied by molecular mechanics simulations. As longer dications introduce lower density of positive charges in the zeolite, the density of connectivity defects also decreases. Finally, these long dications cannot easily place each charged imidazolium ring in the two possible orientations (either parallel or perpendicular to 4MR close to F sites) found for the tetramethylene case. Hence, although the three MFI materials display two 19F NMR resonances at similar chemical shifts, their relative intensities strongly vary as a function of the spacer length.

Journal

Dalton TransactionsRoyal Society of Chemistry

Published: May 22, 2018

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