A Transferable Force Field for Predicting Adsorption and Diffusion of Small Molecules in Alkali Metal Exchanged Zeolites with Coupled Cluster Accuracy

Abstract

We present a transferable force field for small adsorbates (CH 4 , CO 2 , O 2 , and N 2 ) in alkali metal (Li, Na, K, Rb, and Cs) exchanged zeolites. The fitting procedure is based on adsorbate−adsorbent interaction energies obtained from periodic density functional theory calculations and corrected using coupledcluster methods applied to small clusters. The fitting approach aims at accurate prediction of both adsorption and diffusion properties by using sets of configurations that sample adsorption sites and intracrystalline hopping transition states. The quality of the force field is assessed for a wide range of adsorbates in zeolites with different chemical composition and topologies, showing good agreement between theoretical predictions and experimental measurements of adsorption and diffusion.

Computational Screening of Cationic Zeolites for n-Butane/Methane Separations Using Quantitatively Accurate First-Principles-Derived Force Fields

“…It also includes bonded parameters (bond, angle, and torsion terms) so it can describe intra-alkane interactions that are responsible for the flexibility of long alkane molecules. The parameters for methane were not included in the work of Chang and Sandler, so we developed them . The modified OPLS-AA parameters are summarized in Table S1.…”

Screening of Alkali Metal-Exchanged Zeolites for Nitrogen/Methane Separation

“…This force field is transferable to all alkali metal aluminosilicate zeolites with coupled-cluster accuracy. This force field has been validated against previously published experimental data for different zeolite structures to show reliable results …”

“…We employed the force field parameters from Boulfelfel et al 29 to calculate the interaction between the gas molecules (N 2 and CH 4 ) and zeolite atoms as well as the interaction between the cation and framework. This force field is transferable to all alkali metal aluminosilicate zeolites with coupled-cluster accuracy.…”

“…This force field has been validated against previously published experimental data for different zeolite structures to show reliable results. 29 The standard GCMC simulations were performed to determine adsorption isotherms and isosteric heats of adsorption, in which the volume (V), temperature (T), and chemical potential (μ) were kept constant and the number of adsorbate molecules was allowed to change. The RASPA 30,31 code was used to run GCMC simulations.…”

Nitrogen rejection in natural gas using NaZSM-25 zeolite

“…All atoms of the silica structure were kept fixed while cations and gas molecules were allowed to move. Adsorbate-adsorbate and adsorbate-adsorbent interaction parameters were taken from Boulfelfel et al 29 Each system was simulated for 4.7 nanoseconds with a timestep of 0.5 femtosecond in the NVT ensemble. Fig.…”