Inverse CO 2 /C 2 H 2 Separation with MFU-4 and Selectivity Reversal via Postsynthetic Ligand Exchange.

Although many porous materials, including metal-organic frameworks (MOFs), have been reported to selectively adsorb C H in C H /CO separation processes, CO -selective sorbents are much less common. Here, we report the remarkable performance of MFU-4 (Zn Cl (bbta) , bbta=benzo-1,2,4,5-bistriazolate) toward inverse CO /C H separation. The MOF facilitates kinetic separation of CO from C H , enabling the generation of high purity C H (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C H is excluded from MFU-4 by narrow pore windows formed by Zn-Cl groups. Postsynthetic F /Cl ligand exchange was used to synthesize an analogue (MFU-4-F) with expanded pore apertures, resulting in equilibrium C H /CO separation with reversed selectivity compared to MFU-4. MFU-4-F also exhibits a remarkably high C H adsorption capacity (6.7 mmol g ), allowing fuel grade C H (98 % purity) to be harvested from C H /CO mixtures by room temperature desorption.