Metal–Organic Frameworks with Metal–Catecholates\nfor O₂/N₂ Separation

Abstract

Oxygen\nand nitrogen are widely produced feedstocks with diverse fields of applications but are\nprimarily obtained via the energy-intensive cryogenic distillation\nof air. More energy-efficient processes are desirable, and materials\nsuch as zeolites and metal–organic frameworks (MOFs) have been\nstudied for air separation. Inspired by recent theoretical work identifying\nmetal–catecholates for enhancement of O₂ selectivity\nMOFs, the computation-ready experimental database of MOF structures\nwas screened to identify promising candidates for incorporation of\nmetal–catecholates. On the basis of structural requirements,\npreliminary Grand-Canonical Monte Carlo simulations, and further constraints\nto ensure the computational feasibility, over 5000 structures were\neliminated and four MOFs (UiO-66­(Zr), Ce–UiO-66, MOF-5, and\nIRMOF-14) were treated with periodic density functional theory (DFT).\nMetal–catecholates (Mg, Co, Ni, Zn, and Cd) were selected on\nthe basis of cluster DFT calculations and were added to the shortlisted\nMOFs. Periodic DFT was used to compute O₂ and N₂ binding energies near metal–catecholates. We find that the\nbinding energies are primarily dependent on the metals in the metal–catecholates,\nall of which bind O₂ quite strongly (80–258 kJ/mol)\nand have weaker binding for N₂ (3–148 kJ/mol). Of\nthose studied here, Cd-catecholated MOFs are identified as the most\npromising.