Synergistic binding sites in a hybrid ultramicroporous material for one-step ethylene purification from ternary C ₂ hydrocarbon mixtures

Abstract

One-step separation of C₂H₄ from ternary C₂H₂/C₂H₄/C₂H₆ hydrocarbon mixtures is of great significance in the industry but is challenging due to the similar sizes and physical properties of C₂H₂, C₂H₄, and C₂H₆. Here, we report an anion-pillared hybrid ultramicroporous material, CuTiF₆-TPPY, that has the ability of selective recognition of C₂H₄ over C₂H₂ and C₂H₆. The 4,6-connected <i>fsc</i> framework of CuTiF₆-TPPY exhibits semi-cage-like one-dimensional channels sustained by porphyrin rings and TiF₆^2- pillars, which demonstrates the noticeably enhanced adsorption of C₂H₂ and C₂H₆ over C₂H₄. Dynamic breakthrough experiments confirm the direct and facile high-purity C₂H₄ (>99.9%) production from a ternary gas mixture of C₂H₂/C₂H₆/C₂H₄ (1/9/90, v/v/v) under ambient conditions. Computational studies and in situ infrared reveal that the porphyrin moieties with large π-surfaces form multiple van der Waals interactions with C₂H₆; meanwhile, the polar TiF₆^2- pillars form C-H•••F hydrogen bonding with C₂H₂. In contrast, the recognition sites for C₂H₄ in the framework are less marked.