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 (1a-apz), assembled by rigid Mg2(dobdc) (1a) 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 (TA). 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 1a-apz that comprises self-adaption of apz, multiple binding sites, and complementary electrostatic potential (ESP). Breakthrough tests suggest that 1a-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).