Atomistic mechanism of the adsorption of CFCs in zeolite as investigated by Monte Carlo simulation

We studied the adsorption mechanism of CF₂Cl₂ in CsNaY zeolite by using grand canonical Monte Carlo (GCMC) method. The accurate distribution of Al³⁺, Cs⁺, and Na⁺ in the CsNaY (Si/Al = 2.43) was obtained from molecular dynamics (MD) calculations and NMR simulation, while the potential parameters of the CF₂Cl₂ were determined by density functional theory (DFT) calculations. The experimental adsorption isotherm of the CF₂Cl₂ in the CsNaY was fully reproduced by the GCMC simulations. Furthermore, computer graphics (CG) visualization of the calculated results revealed the presence of two different mechanisms of CF₂Cl₂ adsorption in the CsNaY : (1) at low pressure, the CF₂Cl₂ selectively and drastically adsorbed at the Cs⁺ cations of the CsNaY : (2) at high pressure, the aggregation of the CF₂Cl₂ in the super cages of the CsNaY occurred. These results indicate that our new methodology, i. e. the combination of GCMC, MD, NMR simulation, DFT, and CG, is effective and useful not only to reproduce the experimental adsorption isotherm of chlorofluorocarbons in zeolites but also to clarify the atomistic mechanism of the adsorption, which cannot be obtained experimentally.