Magnetically Recoverable Heterogeneous Catalyst: Tungstate Intercalated Mg-Al-Layered Double Hydroxides-Encapsulated Fe.sub.3O.sub.4 Nanoparticles for Highly Efficient Selective Oxidation of Sulfides with H.sub.2O.sub.2

High catalytic activity of tungstate intercalated in hydrotalcite-encapsulated magnetic Fe.sub.3O.sub.4 nanoparticles have been prepared. High resolution transmission electron microscopy characterization demonstrated the formation of Fe.sub.3O.sub.4 nanoparticles within LDH matrix with a mean diameter of 1-3 nm. The catalyst of WO.sub.4.sup.2-/LDH@Fe.sub.3O.sub.4 exhibited excellent catalytic activity for the oxidation of various sulfides. The magnetic properties of the WO.sub.4.sup.2-/LDH@Fe.sub.3O.sub.4 provided a convenient route for separation of the catalyst from the reaction mixture by application of an external permanent magnet. The spent catalyst could be recycled without appreciable loss of catalytic activity.