Hofmann-type metal-organic frameworks with high open metal sites density for efficient propylene/propane separation

Abstract

Exploring new adsorbents for efficient separation of propylene (C3H6) from propane (C3H8) is a critical task. Here we report three Hofmann-type metal-organic frameworks, Ni(Pyz)[Ni(CN)4], Fe(Pyz)[Ni(CN)4], and Co(Pyz)[Ni(CN)4] (termed as NiNi-Pyz, FeNi-Pyz, and CoNi-Pyz, respectively, Pyz = pyrazine), featuring narrow pore size and high open metal sites (OMSs) density for selective C3H6/C3H8 separation. Among them, NiNi-Pyz is the outstanding one that shows the best separation performance. NiNi-Pyz exhibits high volumetric C3H6 uptake of 102.3 cm3 cm−3 and C3H6/C3H8 selectivity of 7.8 under ambient conditions. Binary breakthrough studies corroborate the practical C3H6/C3H8 separation capability of NiNi-Pyz, with high C3H6 productivity of 3.0 mmol g−1. The primary binding sites on NiNi-Pyz, FeNi-Pyz, and CoNi-Pyz are verified by molecular simulations, which confirm that the pore of NiNi-Pyz is slightly smaller than the other two frameworks, resulting in greater host-guest interactions. Additionally, NiNi-Pyz has excellent chemical and thermal stability, and excellent reusability. Combined with low cost and facile synthesis, NiNi-Pyz has promising applications for C3H6/C3H8 separation.