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

Abstract

AbstractOne‐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 ZrF62− 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.