Spatial Distribution of Nitrogen Binding Sites in Metal-Organic Frameworks for Selective Ethane Adsorption and One-Step Ethylene Purification

The one-step purification of ethylene (C2H4) from mixtures containing ethane (C2H6) and acetylene (C2H2) is an industrially important yet challenging process. In this work, we present a site-engineering strategy aimed at manipulating the spatial distribution of binding sites within a confined pore space. We realized successfully by incorporating nitrogen-containing heterocycles, such as indole-5-carboxylic acid (Ind), benzimidazole-5-carboxylic acid (Bzz), and indazole-5-carboxylic acid (Izo), into the robust MOF-808 platform via post-synthetic modification. The resulting functionalized materials, namely MOF-808-Ind, MOF-808-Bzz, and MOF-808-Izo, demonstrated significantly improved selectivity for C2H2 and C2H6 over C2H4. MOF-808-Bzz with two uniformly distributed nitrogen binding sites gave the optimal geometry for selective ethane trapping through multiple strong C-H & sdot;& sdot;& sdot;N hydrogen bonds, leading to the highest C2H2/C2H4 and C2H6/C2H4 combined selectivities among known MOFs. Column breakthrough experiments validated its ability to purify C2H4 from ternary C2H2/C2H4/C2H6 mixtures in a single step. The metal-Organic framework MOF-808-Bzz, which incorporates benzimidazole into MOF-808, features two dispersed nitrogen atoms. It demonstrates remarkable performance in the one-step purification of ethylene from ternary mixtures. The strategically positioned active sites create an optimal geometry, facilitating the efficient entrapment of ethane molecules through the formation of multiple robust C-H & sdot;& sdot;& sdot;N hydrogen bonds and C-H & sdot;& sdot;& sdot;pi interactions.+image

Automated summary

In this work, a site-engineering strategy was employed to manipulate the spatial distribution of binding sites within a confined pore space, enabling the one-step purification of ethylene from mixtures. By incorporating nitrogen-containing heterocycles into the MOF-808 platform via post-synthetic modification, the resulting functionalized materials showed significantly improved selectivity for ethane, demonstrating the ability to efficiently capture ethane molecules.