Defect-engineered MOF-801 for cycloaddition of CO2 with epoxides

Abstract

Heterogeneous catalysts based on defective metal–organic frameworks (MOFs) have attracted wide attention due to their facile formation of defects during synthesis. Herein, two MOFs, MOF-801(D) and MOF-801(P), were synthesized by a solvothermal method using a modulation approach. The synthesized MOFs were characterized by using PXRD, N₂ BET, TGA, NH₃ and CO₂-TPD, CO₂ adsorption isotherms, XPS, FT-IR, FE-SEM, and HR-TEM. A computational characterization method was developed to approximate the degree of defects using a combination of molecular simulation and a linear programming approach. Master isotherm models for N₂ isotherms at 77 K were constructed to match the experimental isotherm data of MOF-801(D) and MOF-801(P), and the pore size distribution and the degree of defects were quantified based on the predicted N₂ isotherms at 77 K. MOF-801(D) showed a high conversion of epoxide with >99% selectivity toward cyclic carbonate and 92% conversion under mild and solvent-less reaction conditions. MOF-801(D) was easily separated using a centrifuge and can be recycled up to 5 times without any significant decrease in its initial performance. Density functional theory (DFT) calculations were carried out to corroborate that the increased acid sites, from the cluster defects, are responsible for the increased catalytic conversion of the catalyst.