Cage Engineering in Anion-Pillared MOFs for Benchmark One-Step C2H4 Purification from Ternary C2H2/CO2/C2H4 Mixtures.

One-step purification of ethylene (C2H4) from the ternary mixtures of acetylene/carbon dioxide/ethylene (C2H2/CO2/C2H4) is a critical industrial challenge due to their similar physical and chemical properties. Herein, we reported a cage engineering strategy in anion-pillared metal-organic frameworks (APMOFs) for efficient C2H2 and CO2 capture simultaneously. Specifically, two stable ZrF6 2- anion-pillared cage-type MOFs (ZNU-17 and ZNU-27) are prepared with both ultramicroporous (∼4 Å) and microporous (>7 Å) cages but featuring different shapes. While ZNU-17 allows the efficient binary C2H2/C2H4 separation, ZNU-27 enables the benchmark ternary C2H2/CO2/C2H4 separation by increasing the adsorption affinity toward CO2. Notably, remarkably increased C2H2 (170.1 cm3 g-1 versus 120.1 cm3 g-1) and CO2 (91.8 cm3 g-1 versus 64.5 cm3 g-1) adsorption capacities are achieved in ZNU-27, and the IAST selectivity of ZNU-27 for CO2/C2H4 is 4.3 times as high as that of ZNU-17 (6.5 versus 1.5). The C2H2, CO2 and C2H4 binding sites in ZNU-27 are studied by gas loaded in situ single crystal structure and density functional theory (DFT) calculation, which revealed that the unique fluorinated 8.5 Å spherical cages provide strong hydrogen binding or electrostatic interactions for C2H2 and CO2. Dynamic breakthrough tests show that from a C2H2/CO2/C2H4 (1/9/90) mixture, polymer-grade C2H4 (≥99.99%) can be obtained in ZNU-27 with a high productivity of 12.04 mol kg-1.