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Magnetically separable catalysts were prepared and employed for the epoxidation of olefins with hydrogen peroxide. In all cases the magnetic core was firstly covered with a silica layer to prevent iron ion-initiated decomposition of hydrogen peroxide. The catalytic active species, an ionic liquid-type peroxotungstate, was then immobilized either by hydrogen bonding (catalyst 1) or by covalent SiO linkage (catalyst 2). In addition to a thorough characterization by FT-IR, XRD, NMR, DRIFT, XPS, and TEM, the catalytic potential was evaluated in the epoxidation of a variety of olefins as well as allylic alcohols. Both catalysts showed essentially a constant activity after at least ten consecutive cycles. On the basis of the research above, a new type of magnetically separable catalyst was constructed by immobilization of lacunary-type phosphotungstate by hydrogen bonding between the sulfonate anion and silanol group on the surface of the core-shell magnetic nanoparticles. After the detailed characterization, the catalyst was used in the epoxidation of a variety of olefins and allylic alcohols and was found to possess high activity, selectivity towards epoxides, and a constant activity after at least ten catalytic recycles without solvent. [ABSTRACT FROM AUTHOR]

Highlights: [•] The combination of zwitterion and phosphotungstate constructed a catalyst. [•] The combined catalyst exhibited high TON and TOF values for expoxidation. [•] The epoxidation can be performed under solventless and ice bath conditions. [•] Strong cooperative effect existed between zwitterions and phosphotungstate. [•] The formation of W/O emulsion by the zwitterion facilitated the reaction. [ABSTRACT FROM AUTHOR]