Metal–Organic Frameworks with Metal–Catecholates for O₂/N₂Separation

Abstract

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, the computation-ready experimental database of MOF structures was screened to identify promising candidates for incorporation of metal–catecholates. On the basis of structural requirements, preliminary Grand-Canonical Monte Carlo simulations, and further constraints to ensure the computational feasibility, over 5000 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 on the basis of cluster DFT calculations and were added to the shortlisted MOFs. Here, 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.