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Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties

The advanced approach for the preparation of the NH(4) form of highly crystalline LSX zeolite under gentle drying conditions (40 °C, membrane pump dynamic vacuum) is discussed. Decationization of this form at moderate temperatures led to the formation of Brønsted acid sites (BASs), whose concentrati...

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Autores principales: Leonova, Aleksandra A., Yashnik, Svetlana A., Paukshtis, Evgeny A., Mel’gunov, Maksim S.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10051662/
https://www.ncbi.nlm.nih.gov/pubmed/36984188
http://dx.doi.org/10.3390/ma16062308
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author Leonova, Aleksandra A.
Yashnik, Svetlana A.
Paukshtis, Evgeny A.
Mel’gunov, Maksim S.
author_facet Leonova, Aleksandra A.
Yashnik, Svetlana A.
Paukshtis, Evgeny A.
Mel’gunov, Maksim S.
author_sort Leonova, Aleksandra A.
collection PubMed
description The advanced approach for the preparation of the NH(4) form of highly crystalline LSX zeolite under gentle drying conditions (40 °C, membrane pump dynamic vacuum) is discussed. Decationization of this form at moderate temperatures led to the formation of Brønsted acid sites (BASs), whose concentration and strength were characterized by IR spectroscopy. It was found that a maximum concentration of three BASs per unit cell can be achieved at 200 °C prior to the initiation of zeolite structure degradation. The proton affinity of BASs is unusual, and aspires 1240 kJ/mol, which is significantly higher compared to faujasites with higher moduli. The increase in temperature of the heat treatment (up to 300 °C) resulted in thermal decomposition of BASs and the manifestation of amorphous phase with corresponding Lewis acid sites (LASs) as well as terminal Si–OH groups. Both the destruction of BASs and formation of the LAS-containing amorphous phase are the key reasons for the significant decrease in the adsorption capacity in the micropore region revealed for the sample decationized at 300 °C.
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spelling pubmed-100516622023-03-30 Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties Leonova, Aleksandra A. Yashnik, Svetlana A. Paukshtis, Evgeny A. Mel’gunov, Maksim S. Materials (Basel) Article The advanced approach for the preparation of the NH(4) form of highly crystalline LSX zeolite under gentle drying conditions (40 °C, membrane pump dynamic vacuum) is discussed. Decationization of this form at moderate temperatures led to the formation of Brønsted acid sites (BASs), whose concentration and strength were characterized by IR spectroscopy. It was found that a maximum concentration of three BASs per unit cell can be achieved at 200 °C prior to the initiation of zeolite structure degradation. The proton affinity of BASs is unusual, and aspires 1240 kJ/mol, which is significantly higher compared to faujasites with higher moduli. The increase in temperature of the heat treatment (up to 300 °C) resulted in thermal decomposition of BASs and the manifestation of amorphous phase with corresponding Lewis acid sites (LASs) as well as terminal Si–OH groups. Both the destruction of BASs and formation of the LAS-containing amorphous phase are the key reasons for the significant decrease in the adsorption capacity in the micropore region revealed for the sample decationized at 300 °C. MDPI 2023-03-13 /pmc/articles/PMC10051662/ /pubmed/36984188 http://dx.doi.org/10.3390/ma16062308 Text en © 2023 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Leonova, Aleksandra A.
Yashnik, Svetlana A.
Paukshtis, Evgeny A.
Mel’gunov, Maksim S.
Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties
title Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties
title_full Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties
title_fullStr Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties
title_full_unstemmed Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties
title_short Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties
title_sort unusual acid sites in lsx zeolite: formation features and physico-chemical properties
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10051662/
https://www.ncbi.nlm.nih.gov/pubmed/36984188
http://dx.doi.org/10.3390/ma16062308
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