Steric‐Relief Ligand Engineering in Aluminum MOFs: Unlocking Supramolecular Recognition for Efficient Propylene/Ethylene Separation

The energy‐efficient separation of propylene (C 3 H 6 ) and ethylene (C 2 H 4 ) is a pivotal yet challenging industrial process, frequently hampered by the trade‐off between adsorption capacity and selectivity, where excessive functionalization often causes severe pore congestion. Herein, we report a “steric‐relief” ligand engineering strategy to overcome this over‐congestion bottleneck in robust aluminum‐based metal–organic frameworks (MOFs). By incorporating non‐functionalized fumarate ligands into a sterically congested methyl‐fumarate parent framework (Al‐MeFum), we successfully constructed a mixed‐ligand solid solution, Al‐Fum‐MeFum, with an optimized pore environment. This strategy effectively alleviates the excessive steric hindrance while re‐exposing specific supramolecular binding sites. Consequently, Al‐Fum‐MeFum exhibits a significantly enhanced BET surface area (818 m 2 g −1 ) and a high C 3 H 6 uptake capacity (85.21 cm 3 g −1 ), coupled with a highly competitive IAST C 3 H 6 /C 2 H 4 selectivity of 20.32. Crucially, dynamic breakthrough experiments confirm the efficient production of polymer‐grade C 2 H 4 (>99.9%) with a remarkable productivity of 42.2 cm 3 g −1 , fully satisfying industrial purification requirements. Density functional theory (DFT) calculations elucidate that the engineered “pockets” provide optimal steric matching and host‐guest interactions for C 3 H 6 . This work not only presents a highly competitive adsorbent but also validates a versatile strategy for fine‐tuning the pore microenvironment of stable MOFs for light hydrocarbon separations.