Cargando…
On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity
Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a L...
Autores principales: | , , |
---|---|
Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
The Royal Society of Chemistry
2021
|
Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8179490/ https://www.ncbi.nlm.nih.gov/pubmed/34163680 http://dx.doi.org/10.1039/d0sc06130a |
_version_ | 1783703793618124800 |
---|---|
author | Ravi, Manoj Sushkevich, Vitaly L. van Bokhoven, Jeroen A. |
author_facet | Ravi, Manoj Sushkevich, Vitaly L. van Bokhoven, Jeroen A. |
author_sort | Ravi, Manoj |
collection | PubMed |
description | Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a Lewis acid site and its formation is accompanied by a loss in Brønsted acidity. Herein, we show that such Lewis acid sites have a preferred location in the pore structure of mordenite. A greater proportion of these Lewis acid sites resides in the side-pockets than in the main channel. By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Brønsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites. Thereby, reversible octahedral–tetrahedral aluminum coordination provides a means to indirectly switch between Lewis and Brønsted acidity. This phenomenon is unique to Lewis acidity that is inherent to the framework, thereby distinguishing it from Lewis acidity originating from extra-framework species. Furthermore, the transformation of framework aluminum into octahedral coordination is decoupled from the generation of distorted tetrahedrally coordinated aluminum, where the latter gives rise to the IR band at 3660 cm(−1) in the OH stretching region. |
format | Online Article Text |
id | pubmed-8179490 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2021 |
publisher | The Royal Society of Chemistry |
record_format | MEDLINE/PubMed |
spelling | pubmed-81794902021-06-22 On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity Ravi, Manoj Sushkevich, Vitaly L. van Bokhoven, Jeroen A. Chem Sci Chemistry Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a Lewis acid site and its formation is accompanied by a loss in Brønsted acidity. Herein, we show that such Lewis acid sites have a preferred location in the pore structure of mordenite. A greater proportion of these Lewis acid sites resides in the side-pockets than in the main channel. By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Brønsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites. Thereby, reversible octahedral–tetrahedral aluminum coordination provides a means to indirectly switch between Lewis and Brønsted acidity. This phenomenon is unique to Lewis acidity that is inherent to the framework, thereby distinguishing it from Lewis acidity originating from extra-framework species. Furthermore, the transformation of framework aluminum into octahedral coordination is decoupled from the generation of distorted tetrahedrally coordinated aluminum, where the latter gives rise to the IR band at 3660 cm(−1) in the OH stretching region. The Royal Society of Chemistry 2021-01-26 /pmc/articles/PMC8179490/ /pubmed/34163680 http://dx.doi.org/10.1039/d0sc06130a Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/ |
spellingShingle | Chemistry Ravi, Manoj Sushkevich, Vitaly L. van Bokhoven, Jeroen A. On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity |
title | On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity |
title_full | On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity |
title_fullStr | On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity |
title_full_unstemmed | On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity |
title_short | On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity |
title_sort | on the location of lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between brønsted and lewis acidity |
topic | Chemistry |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8179490/ https://www.ncbi.nlm.nih.gov/pubmed/34163680 http://dx.doi.org/10.1039/d0sc06130a |
work_keys_str_mv | AT ravimanoj onthelocationoflewisacidicaluminuminzeolitemordeniteandtheroleofframeworkassociatedaluminuminmediatingtheswitchbetweenbrønstedandlewisacidity AT sushkevichvitalyl onthelocationoflewisacidicaluminuminzeolitemordeniteandtheroleofframeworkassociatedaluminuminmediatingtheswitchbetweenbrønstedandlewisacidity AT vanbokhovenjeroena onthelocationoflewisacidicaluminuminzeolitemordeniteandtheroleofframeworkassociatedaluminuminmediatingtheswitchbetweenbrønstedandlewisacidity |