Stability of Zeolite MCM-22 with Varying Si/Al Ratios: A Solid-State NMR Investigation
SCIE
SCOPUS
- Title
- Stability of Zeolite MCM-22 with Varying Si/Al Ratios: A Solid-State NMR Investigation
- Authors
- Abraham, A; Hong, SB; Prins, R; van Bokhoven, JA
- Date Issued
- 2005-01
- Publisher
- ELSEVIER BV
- Abstract
- Determination of the local environment of aluminum in zeolites after various post-synthesis treatments is important for understanding structure-performance relationships. MCM-22 zeolites, synthesized with different silicon-to-aluminum ratios, were treated under various conditions: direct calcination in air, calcination in ammonia and oxygen, and ammonia treatment after calcination. The aluminum co-ordination in a zeolitic framework is highly sensitive to the treatments. The aluminum distribution over crystallographic T-sites in the zeolitic framework was followed by Al-27 MAS and Al-27 MQ-MAS NMR experiments. Loss of tetrahedrally co-ordinated aluminum on several T-sites and appearance of octahedrally coordinated aluminum was observed after calcination, Higher Si/Al ratios result in less octahedrally co-ordinated aluminum. This partial structural collapse can be restored by treatment with a base such as ammonia. An increased disorder in the framework is found after the conversion of octahedrally co-ordinated aluminum to tetrahedrally co-ordinated aluminum compared to the starting material.
- Keywords
- ANGLE-SPINNING NMR; MAS NMR; MOLECULAR-SIEVE; ALUMINUM; AL-27; ANALOG; BETA
- URI
- https://oasis.postech.ac.kr/handle/2014.oak/27757
- ISSN
- 0167-2991
- Article Type
- Article
- Citation
- STUDIES IN SURFACE SCIENCE AND CATALYSIS, vol. 158, page. 679 - 686, 2005-01
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