Bis-chlorinated aromatics adsorption in Faujasites investigated by molecular simulation-influence of Na+ cation

Abstract

Molecular simulations have been employed in order to explore at the microscopic scale the adsorption of bis-chlorinated aromatics (1,2- and 1,3-dichlorobenzene) in Faujasite, a large pore openings zeolite. Both, the purely siliceous and the sodium cation exchanged forms of zeolite structures have been respectively considered, aiming to clearly determine the role of the charge compensating cation in the adsorption phenomenon of the investigated aromatics. A suited combination of classical and electronic structure simulation tools provided a clear overall picture of the adsorption process, from both local and global points of view, well matching with the accessible experimental data. The adsorbate preferential locations, adsorbate/zeolite interaction nature and geometry as well as the adsorption energy were extracted from Density Functional Theory calculations. Furthermore, on the basis of classical force fields, the Gibbs ensemble Monte Carlo simulations allowed predicting the room temperature (298 K) adsorption isotherms for the investigated molecules in Faujasite, within the purely siliceous and Na+ exchanged form, with mobile extra-framework cations upon the adsorption process. Finally, we accomplished a detailed analysis of the microscopic mechanism in play along the whole adsorption process, with a special highlight to the understanding of the interaction geometry of the molecule with the sodium cation, in function of its crystallographic site. Location of the charge compensating cation has been found to influence the nature of interaction with the adsorbate molecule.