Sandwich type polyoxometalates encapsulated into the mesoporous material: synthesis, characterization and catalytic application in the selective oxidation of sulfides.

The A-type sandwich polyoxometalates of [(HOSn IV OH) 3 (PW 9 O 34 ) 2 ] 12- (P 2 W 18 Sn 3 ) and [(OCe IV O) 3 (PW 9 O 34 ) 2 ] 12- (P 2 W 18 Ce 3 ) were immobilized for the first time into the porous metal-organic framework MIL-101(Cr). FT-IR, powder X-ray diffraction, SEM-EDX, ICP analysis, N 2 adsorption and thermogravimetric analysis collectively confirmed immobilization and good distribution of polyoxometalates into cages of MIL-101(Cr). The catalytic activities of the homogeneous P 2 W 18 Sn 3 and P 2 W 18 Ce 3 and the corresponding heterogeneous catalysts were examined in the oxidation of sulfides to sulfones with H 2 O 2 as the oxidant at room temperature. The effects of different dosages of polyoxometalates, type of solvent, reaction time, amount of catalyst and oxidant in this catalytic system were investigated. The new P 2 W 18 Sn 3 @MIL-101 and P 2 W 18 Ce 3 @MIL-101 nanocomposites exhibited good recyclability and reusability in at least five consecutive reaction cycles without significant loss of activity or selectivity.