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.