Two Trinuclear-Cluster-Based MOFs with High-Density N Sites for One-Step Natural Gas Purification and MTO Product Separation

Metal-organic frameworks exhibit high adsorption and separation capabilities in the one-step separation of natural gas mixtures and purifying MTO products. In this work, JLU-MOF191 [Ni(II)₂Ni(III)(OH)(PDDA)₃]·5.5DMF·2H₂O and JLU-MOF192 [Co₃(OH)(PDDA)₃]·[(CH₃)₂NH₂]·4DMA·3H₂O were successfully synthesized. JLU-MOF192-Li was obtained through Li⁺ exchange, which involved replacing (CH₃)₂NH₂⁺ inside the anion framework of JLU-MOF192 by Li⁺. Both MOFs possess permanent pores, excellent thermal stability, and notable high BET surface areas. The nitrogen-containing heterocyclic carboxylic acid ligand H₂PDDA provides a large number of N-binding sites inside the channels, which increases the C-H···N interactions between the frameworks and the gases. JLU-MOF191 and JLU-MOF192-Li exhibit high adsorption capacities and Qst for C₃H₈, C₃H₆, and C₂H₆, which endow them with the ability to purify natural gas and MTO products. By changing the metal nodes, JLU-MOF192-Li exhibits higher adsorption and separation capabilities than JLU-MOF191. The DFT theoretical calculation confirmed that JLU-MOF192-Li exhibits a higher adsorption for C₃H₈, C₃H₆, and C₂H₆ compared to C₂H₄ and CH₄. The column penetration experiment demonstrated that JLU-MOF192-Li could respectively obtain methane (purity: 99.9%) and C₂H₄ (purity: 99.9%) from the two mixtures of C₃H₈/C₂H₆/CH₄ and C₃H₆/C₂H₄. The excellent adsorption and separation performances of JLU-MOF192-Li for natural gas and MTO products make it a potential material for industrial applications.