Metal-Organic Frameworks with Metal Catecholates for O₂/N₂ Separation

Demir, H.; Stoneburner, S. J.; Jeong, W.; Ray, D.; Zhang, X.; Farha, O. K.; Cramer, C. J.; Siepmann, J. I.; Gagliardi, L.
J. Phys. Chem. C 2019, 123, 12935 (doi:10.1021/acs.jpcc.9b02848).

Oxygen and nitrogen are widely produced feedstocks with diverse fields of applications, but are primarily obtained via the energy-intensive cryogenic distillation of air. More energy-efficient processes are desirable, and materials such as zeolites and metal-organic frameworks (MOFs) have been studied for air separation. Inspired by recent theoretical work identifying metal-catecholates for enhancement of O₂ selectivity MOFs, in this work the computation-ready experimental (CoRE) database of MOF structures was screened to identify promising candidates for incorporation of metal catecholates. Based on structural requirements, preliminary Grand-Canonical Monte Carlo simulations, and further constraints to ensure the computational feasibility, over 5,000 structures were eliminated and four MOFs (UiO-66(Zr), Ce-UiO-66, MOF-5, and IRMOF-14) were treated with periodic density functional theory (DFT). Metal catecholates (Mg, Co, Ni, Zn, and Cd) were selected based on cluster DFT calculations and were added to the shortlisted MOFs. Periodic DFT was used to compute O₂ and N₂ binding energies near metal catecholates. We find that the binding energies are primarily dependent on the metals in the metal catecholates, all of which bind O₂ quite strongly (80-258 kJ/mol) and have weaker binding for N₂ (3-148 kJ/mol). Of those studied here, Cd-catecholated MOFs are identified as the most promising.