Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9770487 | Journal of Molecular Structure | 2005 | 8 Pages |
Abstract
The structure of industrially important zeolitic catalysts (H-BEA, H-ZSM-5, and H-FAU) and their interactions with benzene have been investigated within the framework of our-own-N-layered integrated molecular orbital+molecular mechanics (ONIOM) approach utilizing the three-layer ONIOM scheme (B3LYP/6-31G(d,p):HF/3-21G:UFF). Inclusion of the extended zeolitic framework covering the nanocavity has an effect on adsorption properties and leads to differentiation of different types of zeolite, unlike the small cluster models which are not able to make this differentiation. The ONIOM adsorption energies of benzene on ZSM-5, BEA, and FAU zeolites are â19.23, â16.11, and â15.22Â kcal/mol, respectively, which agrees well with the known adsorption trend of these three zeolites. On the other hand, the small cluster models underestimate the adsorption energies and even yield an unreasonable trend of adsorption energies (â8.09, â8.48, and â8.93Â kcal/mol for ZSM-5, BEA, and FAU, respectively). With the inclusion of basis set superposition error (BSSE) and the MP2 corrections, the ONIOM3(MP2/6-31G(d,p):HF/3-21G:UFF) adsorption energies are predicted to be â18.96, â16.34, and â15.18Â kcal/mol, for ZSM-5, BEA, and FAU, respectively. The last value can be compared well with the experimental data (â15.31Â kcal/mol) for benzene adsorption on a FAU zeolite. The results derived in this study suggest that the ONIOM3(MP2/6-31G(d,p):HF/3-21G:UFF) scheme provides a more accurate method for investigating the adsorption of aromatic hydrocarbons on these zeolites.
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Authors
Ratana Rungsirisakun, Bavornpon Jansang, Piboon Pantu, Jumras Limtrakul,