The Keggin trimetallic polyoxometalates of [A-β-SiW9Fe3O37]7− and [A-β-SiW9Co3O37]10− were immobilized into the porous metal–organic framework MIL-101(Cr). The structures and properties were characterized with high-resolution transmission electron microscopies (HRTEM), feld emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), powder X-ray difraction (XRD), nitrogen adsorption–desorption isotherm and zeta potential analysis. In this approach, the SiW9Fe3O37@MIL-101 and SiW9Co3O37@MIL-101 composites were synthesized with spherical particles consisting of high surface area (the BET surface area 1368.1 and 1275.8 m2/g respectively) and uniform pore size (2.10 and 2.13 nm respectively). The SiW9Fe3O37@MIL-101 and SiW9Co3O37@MIL- 101 catalysts demonstrated exceptional performance in synthesizing 5-substituted 1H tetrazoles and oxidation sulfde to sulfones. Incorporating SiW9Fe3O37 and SiW9Co3O37 polyoxometalates into the MIL-101 matrix provided a high surface area and this unique structure allowed enhanced accessibility of reactants to the catalytic sites.
