Extraction combined oxidation desulfurization of dibenzothiophene using polyoxometalate-supported magnetic chitosan microspheres

In this study, Keggin- and Dawson-type polyoxometalates (POMs) were immobilized on chitosan (CS)-modified Fe 3 O 4 @CS by electrostatic interaction for the preparation of heterogeneous catalysts Fe 3 O 4 @CS@POM (POM=PMo 12 , PW 12 , SiW 12 , P 2 W 17 , or P 2 W 18 ). The oxidative desulfurization (ODS) of dibenzothiophene (DBT) by Fe 3 O 4 @CS@POMs was evaluated. It is found that Fe 3 O 4 @CS@POM shows the good ODS performance due to the good dispersion of POM on Fe 3 O 4 surface and the good accessibility of substrate to it leaded by the full swelling of the cross-linked CS in acetonitrile . The catalytic activity follows the order of Fe 3 O 4 @CS@PMo 12 > Fe 3 O 4 @CS@PW 12 > Fe 3 O 4 @CS@P 2 W 17 > Fe 3 O 4 @CS@P 2 W 18 > Fe 3 O 4 @CS@SiW 12 . At 333 K, the desulfurization rate of DBT (500 ppm) reaches 99.7% at 60 min and 100% at 90 min in the presence of 0.1 g of Fe 3 O 4 @CS@PMo 12 and 100 µL of H 2 O 2 . The ODS process can be well described by the pseudo-first-order kinetic model (R 2  > 0.99) with a high kinetic constant (0.0761 min −1 ) and a low apparent activation energy (60.57 kJ / mol). In addition, the as-prepared catalyst can be easily separated and recycled in the external magnetic field, and it still has the good reusability for several times, stemming from the stable encapsulation of POM clusters by cross-linked chitosan on Fe 3 O 4 surface.