Construction of a Porous Metal–Organic Framework with a High Density of Open Cr Sites for Record N₂/O₂ Separation

Abstract

The removal of low concentration N₂ is of great significance and challenging in the industrial production of high-purity O₂ . Herein, a chromium-based metal-organic framework, namely, TYUT-96Cr, is reported, which has an unprecedented N₂ capture capacity of 37.46 cm³ cm^-3 and N₂ /O₂ (5:95, v/v) selectivity up to 26.95 (298 K and 1 bar), thus setting new benchmarks for all reported metal-organic frameworks and commercially used ones (Li-LSX and 13X). Breakthrough experiments reveal that N₂ can be directly extracted from various N₂ /O₂ (79:21, 50:50, 5:95, and 1:99, v/v) mixtures by this material, affording a record-high O₂ -production scale with 99.99% purity. Density functional theory calculations and in situ infrared spectroscopy studies demonstrate that the high-density open Cr (III) sites in TYUT-96Cr can behave as effective Lewis acidic sites, thus resulting in a strong affinity toward N₂ . The high N₂ adsorption selectivity, exceptional separation performance, and ultrahigh structural stability render this porous material with great potential for this important industrial application.