Efficient Trapping of Trace Acetylene from Ethylene in an Ultramicroporous Metal-Organic Framework: Synergistic Effect of High-Density Open Metal and Electronegative Sites.

Acetylene (C2 H2 ) removal from ethylene (C2 H4 ) is a crucial step in the production of polymer-grade C2 H4 but remains a daunting challenge because of the similar physicochemical properties of C2 H2 and C2 H4 . Currently energy-intensive cryogenic distillation processes are used to separate the two gases industrially. A robust ultramicroporous metal-organic framework (MOF), Ni3 (pzdc)2 (7 Hade)2 , is reported for efficient C2 H2 /C2 H4 separation. The MOF comprises hydrogen-bonded linked one-dimensional (1D) chains, and features high-density open metal sites (2.7 nm-3 ) and electronegative oxygen and nitrogen sites arranged on the pore surface as cooperative binding sites. Theoretical calculations, in situ powder X-ray diffraction and Fourier-transform infrared spectroscopy revealed a synergistic adsorption mechanism. The MOF possesses S-shaped 1D pore channels that efficiently trap trace C2 H2 at 0.01 bar with a high C2 H2 uptake of 60.6 cm3  cm-3 and C2 H2 /C2 H4 selectivity.