2012
ACL
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Zalfa Nour, Dorothée Berthomieu, Qingyuan Yang, Guillaume Maurin, 'A Computational Exploration of the CO Adsorption in Cation-Exchanged Faujasites', J. Phys. Chem. C 116 24512–24521 (2012) doi:10.1021/jp305145s
Molecular simulations have been employed to explore at the microscopic scale the adsorption of CO in two families of sodium exchanged faujasite, i.e. NaX and NaY. As a preliminary step, Density Functional Theory calculations have been conducted to derive new sets of potential parameters for accurately describing the interactions between CO and the extra-framework cations present within the supercage that act as preferential adsorption sites for the guest molecules. Two different parameterizations have been considered to discriminate the Na+ sites, i.e. Na+SII and Na+SIII’, involved in the interactions with CO. Based on these forcefields, Grand Canonical Monte Carlo simulations were further realized to first predict the adsorption properties (isotherms and enthalpies) of these two types of faujasites up to high pressure. This was followed by a careful analysis of the microscopic mechanism in play along the whole adsorption process with a special emphasis on understanding the arrangements of CO in the vicinity of the Na+ whether they occupy SII or SIII’ sites. These findings were discussed in light of the enthalpy profile obtained as a function of the loading and a few experimental data available in the literature. Finally, complementary simulations were realized with mobile extra-framework cations upon CO adsorption. It was evidenced that Na+SII can migrate toward SIII’ sites in NaY, while in NaX, there is no cation redistribution within the supercage due to a steric hindrance. Such cation dynamics were shown to not drastically affect the adsorption properties of both Faujasites, however, this is a critical pre-requisite to allow CO to form a double type interaction with both Na+SIII’ and Na+SII via its C- and O-ends respectively, as predicted in cation-exchanged zeolites using quantum chemical calculations.
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