Optimal Binding Affinity for Sieving-Type Separation of Propylene from Propane in an Oxyfluoride Anion-Based Metal-Organic Framework

Highly efficient adsorptive separation of propylene from propane offers an ideal alternative method to replace the energy-intensive cryogenic distillation technology. Molecular sieving-type separation via high-performance adsorbents is targeted for the superior selectivity but the limit in adsorption capacity remains a great challenge. Here we report an oxyfluoride-based ultramicroporous metal-organic framework <b>UTSA-400</b>, [Ni(WO₂F₄)(pyz)₂] (pyz = pyrazine), featuring one-dimensional pore channels that can accommodate the propylene molecules with optimal binding affinity while specifically exclude the propane molecules. The exposed oxide/fluoride pair sites in <b>UTSA-400</b> serve as strong functional sites for strengthened propylene-host interactions, resulting in a significantly enhanced adsorption uptake, while the propane molecules are excluded due to the regulated host dynamics. The strong propylene binding enables near saturation of propylene in the pore confinement at ambient conditions, leading to full utilization of pore space and superior packing density. Dispersion-corrected density functional theory calculations and <i>in situ</i> infrared spectroscopy clearly unveil the nature of boosted host-guest binding. Direct production of polymer-grade (&gt;99.5%) propylene with remarkable dynamic productivity is demonstrated by column breakthrough experiments. This work presents a feasible strategy to break the trade-off in adsorptive separation through guest binding optimization in molecular sieve.