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Abstract Two‐dimensional MFI zeolite nanosheets contain Brønsted acid sites partially confined at the intercept between micro‐ and mesopores. These acid sites exhibit exceptional reactivities and stabilities for C=C bond coupling and ring‐closure reactions that transform light aldehydes to aromatics. These sites are much more effective than those confined within the micropores of MFI crystallites and those unconfined on H4SiW12O40clusters or mesoporous aluminosilicate Al‐MCM‐41. The partially confined site environment solvates and stabilizes the transition states of the kinetically relevant steps during aromatization.
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Rigid Arrangements of Ionic Charge in Zeolite Frameworks Conferred by Specific Aluminum Distributions Preferentially Stabilize Alkanol Dehydration Transition States
Abstract Zeolite reactivity depends on the solvating environments of their micropores and the proximity of their Brønsted acid sites. Turnover rates (per H+) for methanol and ethanol dehydration increase with the fraction of H+sites sharing six‐membered rings of chabazite (CHA) zeolites. Density functional theory (DFT) shows that activation barriers vary widely with the number and arrangement of Al (1–5 per 36 T‐site unit cell), but cannot be described solely by Al–Al distance or density. Certain Al distributions yield rigid arrangements of anionic charge that stabilize cationic intermediates and transition states via H‐bonding to decrease barriers. This is a key feature of acid catalysis in zeolite solvents, which lack the isotropy of liquid solvents. The sensitivity of polar transition states to specific arrangements of charge in their solvating environments and the ability to position such charges in zeolite lattices with increasing precision herald rich catalytic diversity among zeolites of varying Al arrangement.
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- PAR ID:
- 10187774
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 42
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 18686-18694
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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