Design of hierarchically porous Zr-MOFs with reo topology and confined PMA for ultra-efficient oxidation desulfurization

Abstract

It is challenging but desirable to synthesize hierarchically porous MOFs (HP-MOFs) with well-defined topology. Herein, a series of HP-Zr-MOFs (H-UiO-66-X) with different topologies were synthesized through an in situ self-assembly template strategy. Further, H3PMo12O40 (PMA) was dispersed within H-UiO-66-X to illustrate the confinement effect of HP-MOFs on PMA as ultra-efficient ODS catalysts. Potentiometric acid–base titration is used to evaluate three typical types of Brønsted acid protons (μ3–OH, Zr-OH2, and Zr-OH) presented in the nodes of defect HP-MOFs according to their different pKa values (∼3, ∼6 and ∼8). By quantifying the amount of defect sites (Zr-OH2 and Zr-OH) resulting from either missing Zr6O8 clusters or missing linkers in the HP-MOFs, the information about the true topology of HP-MOFs is provided. The Zr-OH2 defects are correlated to missing Zr6O8 cluster and the Zr-OH defects are related to missing linkers. The loaded PMA molecules mainly occupy the Zr-OH2 defect sites by the substitution of H2O molecules and still maintain the Keggin structure. The results give deep insight on the structure-activity relationship for PMA confined in HP-Zr-MOFs with clear topologies.