Cage Engineering in Anion-Pillared MOFs for Benchmark One-Step CH Purification from Ternary CH/CO/CH Mixtures.

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