期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 115, 期 30, 页码 14754-14761出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp201454t
关键词
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资金
- National Natural Science Foundation of China [10774126, 20923004]
- Ministry of Science and Technology [2007CB815206, 2011CB808504]
There exist 12 crystallographically distinct Al-sites in the ZSM-5 zeolite, associated with which there are various Na-sites. Understanding their locations, while being the key to the understanding of the catalytic properties of this material, remains a great challenge in both experiment and theory. We present here a theoretical survey of the Na+ location along with the Al distribution in ZSM-5 by using hybrid methods, ONIOM (our Own N-layer Integrated molecular Orbital molecular Mechanics) as well as the newly developed extended ONIOM (XO) (Guo, W. P.; Wu, A. A.; Xu, X. Chem. Phys. Lett. 2010, 498, 203-208) method. The reliability and efficiency of different methods/models have been systematically tested. Using the T1 Al-site as an example, our calculations demonstrate that the high-level layers of ONIOM models have to include all rings around the [AlO4] tetrahedron to have reliable coordination structures and energetics of different Na-sites, while XO can provide reliable results with 60% savings of computational time as compared to that of ONIOM. Our XO calculations reveal that, in most Al-sites, Na+ preferentially occupies the six-membered-ring sites, and the most favorable Al-sites along with the Na-sites are T8/M6, T10/Z6, and T4/Z6. Conversely, those Al-sites only surrounded by five-membered rings, such as T6 and T3, are predicted to be energetically unfavorable.
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