| Combined DFT theoretical calculation and solid-state NMR studies of Al substitution and acid sites in zeolite MCM-22. | |
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MedLine Citation:
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PMID: 16375424 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
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The distributions of Brönsted acidic protons and their acid strengths in zeolite H-MCM-22 have been characterized by density functional theory (DFT) calculations as well as magic angle spinning (MAS) NMR experiments. The embedded scheme (ONIOM) that combines the quantum mechanical (QM) description of active sites and semiempirical AM1 treatment of the neighboring environment was applied to predict the aluminum substitution mechanism and proton affinity (PA), as well as adsorption behaviors of acetone and trimethylphosphine oxide (TMPO) onto the zeolite. Our theoretical results indicate that the Al substitution takes place in the order of Al1-OH-Si2 > Al8-OH-Si8 > Al5-OH-Si7. The DFT theoretical and NMR experimental results suggest that the acid strength of the three Brönsted acid sites in H-MCM-22 zeolite is slightly lower than that of H-ZSM-5 zeolite and the accessible Brönsted acidic protons most likely reside in both the supercages (at the Al8-OH-Si8 and Al1-OH-Si2 sites) and external surface pocket (at the Al8-OH-Si8 site) rather than in the sinusoidal channels (Al5-OH-Si7), with the Al1-OH-Si2 site having the strongest acid strength (as probed by TMPO). This may partially explain the special selectivity of acid-catalyzed reactions occurring inside the channels of H-MCM-22 zeolite. |
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Authors:
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Anmin Zheng; Lei Chen; Jun Yang; Mingjin Zhang; Yongchao Su; Yong Yue; Chaohui Ye; Feng Deng |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The journal of physical chemistry. B Volume: 109 ISSN: 1520-6106 ISO Abbreviation: J Phys Chem B Publication Date: 2005 Dec |
Date Detail:
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Created Date: 2005-12-26 Completed Date: 2006-08-08 Revised Date: 2007-03-23 |
Medline Journal Info:
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Nlm Unique ID: 101157530 Medline TA: J Phys Chem B Country: United States |
Other Details:
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Languages: eng Pagination: 24273-9 Citation Subset: - |
Affiliation:
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State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, China. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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