Issue 37, 2016

Adsorption in zeolites using mechanically embedded ONIOM clusters


We have explored mechanically embedded three-layer QM/QM/MM ONIOM models for computational studies of binding in Al-substituted zeolites. In all the models considered, the high-level-theory layer consists of the adsorbate molecule and of the framework atoms within the first two coordination spheres of the Al atom and is treated at the M06-2X/6-311G(2df,p) level. For simplicity, flexibility and routine applicability, the outer, low-level-theory layer is treated with the UFF. We have modelled the intermediate-level layer quantum mechanically and investigated the performance of HF theory and of three DFT functionals, B3LYP, M06-2X and ωB97x-D, for different layer sizes and various basis sets, with and without BSSE corrections. We have studied the binding of sixteen probe molecules in H-MFI and compared the computed adsorption enthalpies with published experimental data. We have demonstrated that HF and B3LYP are inadequate for the description of the interactions between the probe molecules and the framework surrounding the metal site of the zeolite on account of their inability to capture dispersion forces. Both M06-2X and ωB97x-D on average converge within ca. 10% of the experimental values. We have further demonstrated transferability of the approach by computing the binding enthalpies of n-alkanes (C1–C8) in H-MFI, H-BEA and H-FAU, with very satisfactory agreement with experiment. The computed entropies of adsorption of n-alkanes in H-MFI are also found to be in good agreement with experimental data. Finally, we compare with published adsorption energies calculated by periodic-DFT for n-C3 to n-C6 alkanes, water and methanol in H-ZSM-5 and find very good agreement.

Graphical abstract: Adsorption in zeolites using mechanically embedded ONIOM clusters

Supplementary files

Article information

Article type
13 May 2016
29 Aug 2016
First published
01 Sep 2016
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2016,18, 26094-26106

Adsorption in zeolites using mechanically embedded ONIOM clusters

R. E. Patet, S. Caratzoulas and D. G. Vlachos, Phys. Chem. Chem. Phys., 2016, 18, 26094 DOI: 10.1039/C6CP03266D

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