Induced-Fit-Identification in a Rigid Metal-Organic Framework for ppm-Level CO2 Removal and Ultra-Pure CO Enrichment

Abstract

Removing CO₂ from crude syngas via physical adsorption is an effective method to yield eligible syngas. However, the bottleneck in trapping ppm-level CO₂ and improving CO purity at higher working temperatures are major challenges. Here we report a thermoresponsive metal-organic framework (1 a-apz), assembled by rigid Mg₂ (dobdc) (1 a) and aminopyrazine (apz), which not only affords an ultra-high CO₂ capacity (145.0/197.6 cm³ g^-1 (0.01/0.1 bar) at 298 K) but also produces ultra-pure CO (purity ≥99.99 %) at a practical ambient temperature (T_A ). Several characterization results, including variable-temperature tests, in situ high-resolution synchrotron X-ray diffraction (HR-SXRD), and simulations, explicitly unravel that the excellent property is attributed to the induced-fit-identification in 1 a-apz that comprises self-adaption of apz, multiple binding sites, and complementary electrostatic potential (ESP). Breakthrough tests suggest that 1 a-apz can remove CO₂ from 1/99 CO₂ /CO mixtures at practical 348 K, yielding 70.5 L kg^-1 of CO with ultra-high purity of ≥99.99 %. The excellent separation performance is also revealed by separating crude syngas that contains quinary mixtures of H₂ /N₂ /CH₄ /CO/CO₂ (46/18.3/2.4/32.3/1, v/v/v/v/v).

Keywords: CO2/CO Separation; Induced-Fit-Identification; Metal-Organic Frameworks; Syngas Purification; Thermoresponsive Effect.