Amide-Functionalized Metal-Organic Frameworks Coupled with Open Fe/Sc Sites for Efficient Acetylene Purification

Acetylene (C₂H₂) purification is of great importance for many chemical synthesis and processes. Metal-organic frameworks (MOFs) are widely used for gas adsorption and separation due to their variable structure and porosity. However, the exploitation of ideal MOF adsorbents for C₂H₂ keeps a challenging task. Herein, a combination of open metal sites (OMSs) and Lewis basic sites (LBSs) in robust MOFs is demonstrated to effectively promote the C₂H₂ purification performance. Accordingly, SNNU-37(Fe/Sc), two isostructural MOFs constituted by [Fe₃O(COO)₆] or [Sc₃O(COO)₆] trinuclear clusters and amide-functionalized tricarboxylate linkers, were designed with extra-stable 3,6-connected new architectures. Derived from the coexistence of high-density OMSs and LBSs, the C₂H₂ adsorption amounts of SNNU-37(Fe/Sc) are much higher than those values for C₂H₄ and CO₂. Theoretical IAST selectivity values of SNNU-37(Fe) are 2.4 for C₂H₂/C₂H₄ (50/50, v/v) and 9.9 for C₂H₂/CO₂ (50/50, v/v) at 298 K and 1 bar, indicating an excellent C₂H₂ separation ability. Experimental breakthrough curves also revealed that SNNU-37(Fe) could effectively separate C₂H₂/C₂H₄ and C₂H₂/CO₂ under ambient conditions. GCMC simulations further indicate that open Fe or Sc sites and amide groups mainly contribute to stronger adsorption sites for C₂H₂ molecules.