Rational Assembly of Multifunctional Fe/Mn MOF through Mixed-Linker and Defect Engineering for CO2 Cycloaddition Reaction

Abstract The development of heterogeneous catalysts that cooperatively integrate multiple active sites within a defined architecture is critical for complex reactions such as the cycloaddition of CO2 to epoxides. Herein, a rational design strategy for constructing a defect-engineered bimetallic metal–organic framework (MOF) incorporating multiple catalytic functionalities is demonstrated. Through a mixed-metal (Fe/Mn) and mixed-linker (1,4-benzenedicarboxylic acid/4-aminobenzoic acid) synthesis strategy, a defective Fe/Mn MOF with layered nanosheet morphology was prepared via an ultrasonic-assisted method. This framework simultaneously incorporates: (i) Lewis basic amine functionalities for CO2 interaction and activation, (ii) defect-induced coordinatively unsaturated metal sites serving as Lewis acidic centers for epoxide activation, and (iii) bimetallic nodes that provide a modulated catalytic environment within the framework. Comprehensive characterization including XRD, XPS, 1H NMR, BET, TGA, ICP–OES, and SEM confirms the successful construction of the designed framework and reveals an enhanced surface area compared with its non-defective analogue. Under optimized solvent-free conditions, the catalyst achieved a styrene oxide conversion of 87%, substantially outperforming non-defective and monometallic control MOFs. This work demonstrates a targeted strategy for multifunctional MOF catalysts in which the synergistic integration of mixed-metal chemistry, linker functionalization, defect engineering, and morphology control enhances catalytic performance for sustainable CO2 conversion.