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

Abstract

Abstract One‐step purification of ethylene (C 2 H 4 ) from the ternary mixtures of acetylene/carbon dioxide/ethylene (C 2 H 2 /CO 2 /C 2 H 4 ) 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 C 2 H 2 and CO 2 capture simultaneously. Specifically, two stable ZrF 6 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 C 2 H 2 /C 2 H 4 separation, ZNU‐27 enables the benchmark ternary C 2 H 2 /CO 2 /C 2 H 4 separation by increasing the adsorption affinity toward CO 2 . Notably, remarkably increased C 2 H 2 (170.1 cm 3 g −1 versus 120.1 cm 3 g −1 ) and CO 2 (91.8 cm 3 g −1 versus 64.5 cm 3 g −1 ) adsorption capacities are achieved in ZNU‐27, and the IAST selectivity of ZNU‐27 for CO 2 /C 2 H 4 is 4.3 times as high as that of ZNU‐17 (6.5 versus 1.5). The C 2 H 2 , CO 2 and C 2 H 4 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 C 2 H 2 and CO 2 . Dynamic breakthrough tests show that from a C 2 H 2 /CO 2 /C 2 H 4 (1/9/90) mixture, polymer‐grade C 2 H 4 (≥99.99%) can be obtained in ZNU‐27 with a high productivity of 12.04 mol kg −1 .