3 years ago

Zeolite Adsorption Free Energies from ab Initio Potentials of Mean Force

Zeolite Adsorption Free Energies from ab Initio Potentials
of Mean Force
Hui Li, Christopher Paolucci, William F. Schneider
The ability of metal-exchanged zeolites to chemisorb small gas molecules is key to their performance as heterogeneous catalysts and gas-separating agents. Here, we propose and evaluate an ab initio potential of mean force (PMF) method for computing adsorption free energies of representative small molecules to Cu-exchanged sites in SSZ-13 zeolite. We show that Cu ions are mobilized by adsorbates and, as a result, computed free energies are significantly more negative than those obtained from a conventional harmonic oscillator model. PMF-derived free energies are consistent with available experiment and, in many cases, with a dynamics-based quasi-harmonic analysis (QHA). The PMF approach avoids the artificial partitioning of degrees of freedom intrinsic to the QHA. On the basis of the PMF results, we propose a simple correlation to estimate free energies from computed adsorption energies and gas-phase entropies.

Publisher URL: http://dx.doi.org/10.1021/acs.jctc.7b00716

DOI: 10.1021/acs.jctc.7b00716

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