An investigation for H2/N2 adsorptive separation in SIFSIX-2-Cu-i

Hydrogen recovery from ammonia purge gas is a desirable method to relieve the pressure of increasing demand for hydrogen. Metal-organic frameworks (MOFs) are promising adsorbents for the separation of the H2–N2 mixture. However, the separation of the H2–N2 mixture using MOFs remains challenging due to the lack of adsorptive mechanism. Herein, the adsorption mechanism of the H2–N2 mixture in SIFSIX-2-Cu-i has been systematically investigated with the method of a combination of excess adsorption experiments, molecular simulations, and DFT calculations. In the Grand Canonical Monte Carlo (GCMC) simulations, the polarizable force field was first applied to the adsorption of pure H2 or N2 and H2–N2 mixture in SIFSIX-2-Cu-i. Ab Initio Molecular Dynamics (AIMD) was performed to investigate the distribution of the guest molecules in the pores of SIFSIX-2-Cu-i. Finally, Density functional theory (DFT) calculations were performed to predict the transfer of charge between MOF and guest molecules. Results revealed two binding sites of H2 or N2 in SIFSIX-2-Cu-i. A relatively high thermodynamic adsorption selectivity for N2 over H2 has been observed in SIFSIX-2-Cu-i. Furthermore, SIFSIX-2-Cu-i also exhibits a greater affinity with N2 than with H2, which is probably because of the stronger induction interactions between F2 atoms and N2 molecules. These findings are of significance to guide the design of the new highly selective adsorbents for the separation of H2/N2.