Boosting Adsorption and Selectivity of Acetylene by Nitro Functionalisation in Copper(II)-Based Metal-Organic Frameworks

Abstract

Purification and storage of acetylene (C2H2) are important to many industrial processes. The exploitation of metal -organic framework (MOF) materials to address the balance between selectivity for C2H2 vs carbon dioxide (CO2 ) against maximising uptake of C2H2 has attracted much interest. Herein, we report that the synergy between unsaturated copper (II) sites and functional groups, fluoro (-F), methyl (-CH3), nitro (-NO2) in a series of isostructural MOF materials MFM-190(R) that show exceptional adsorption and selectivity of C2H2 . At 298 K, MFM-190(NO2) exhibits an C2H2 uptake of 216 cm3 g-1 (320 cm3 g-1 at 273 K ) at 1.0 bar and a high selectivity for C2H2/CO2 (up to ~150 for v/v = 2/1) relevant to that in the industrial cracking stream. Dynamic breakthrough studies validate and confirm the excellent separation of C2H2/CO2 by MFM-190(NO2) under ambient conditions. In situ neutron powder diffraction reveals the cooperative binding, packing and selectivity of C2H2 by unsaturated Cu(II) sites and free -NO2 groups.

Keywords: acetylene; carbon dioxide; metal-organic framework; neutron diffraction; separations.