An MOF-Based Single-Molecule Propylene Nanotrap for Benchmark Propylene Capture from Ethylene

Abstract

Highly selective capture and separation of propylene (C₃H₆) from ethylene (C₂H₄) presents one of the most crucial processes to obtain pure C₂H₄ in the petrochemical industry. The separation performance of current physisorbents is commonly limited by insufficient C₃H₆ binding affinity, resulting in poor low-pressure C₃H₆ uptakes or inadequate C₃H₆/C₂H₄ selectivities. Herein, we realize a unique single-molecule C₃H₆ nanotrap in an ultramicroporous MOF material (Co(pyz)[Pd(CN)₄], ZJU-74a-Pd), exhibiting the benchmark C₃H₆ capture capacity at low-pressure regions. This MOF-based nanotrap features the sandwichlike strong multipoint binding sites and the perfect size match with C₃H₆ molecules, providing an ultrastrong C₃H₆ binding affinity with the maximal Q_st value (55.8 kJ mol^–1). This affords the nanotrap to exhibit one of the highest C₃H₆ uptakes at low pressures (60.5 and 103.8 cm³ cm^–3 at 0.01 and 0.1 bar) and record-high C₃H₆/C₂H₄ selectivity (23.4). Theoretical calculations reveal that the perfectly size-matched pore cavities combined with sandwichlike multibinding sites enable this single-molecule C₃H₆ nanotrap to maximize the C₃H₆ binding affinity, mainly accounting for its record low-pressure C₃H₆ capture capacity and selectivity. Breakthrough experiments further confirm its excellent separation capacity for actual 1/99 and 50/50 C₃H₆/C₂H₄ mixtures, affording the remarkably high pure C₂H₄ productivities of 17.1 and 3.4 mol kg^–1, respectively.