Recognition of C₄ Olefins by an Ultramicroporous ftw-Type Yttrium-Based Metal-Organic Framework with Distorted Cages

Developing porous adsorbents for efficient separation of C₄ olefins is significant but challenging in the petrochemical industry due to their similar molecular sizes and physical properties. The separation efficiency is often limited when separating C₄ olefins by a single separation mechanism. Herein, an ultramicroporous yttrium-based MOF, Y-dbai, is reported featuring cage-like pores connected by small windows, for recognition and efficient separation of C₄ olefins through a synergistic effect of thermodynamic and kinetic mechanisms. At 298 K and 1 bar, the adsorption capacities of Y-dbai for C₄H₆, 1-C₄H₈, and i-C₄H₈ are 2.88, 1.07, and 0.14 mmol g^-1, respectively, indicating a molecular sieving effect toward i-C₄H₈. The C₄H₆/i-C₄H₈ and 1-C₄H₈/i-C₄H₈ uptake selectivities of Y-dbai are 20.6 and 7.6, respectively, outperforming most of the reported adsorbents. The static and kinetic adsorption experiments coupled with DFT calculations indicate the separation should be attributed to a combined effect of thermodynamically and kinetically controlled mechanism. Breakthrough experiments have confirmed the excellent separation capability of Y-dbai toward C₄H₆/1-C₄H₈, C₄H₆/i-C₄H_8, and C₄H₆/1-C₄H₈/i-C₄H₈ mixtures.