Magnetically recyclable Ag-ferrite catalysts: general synthesis and support effects in the epoxidation of styrene.

A series of new magnetically recyclable catalysts (MRCs), Ag-M(1-x)Fe(2+x)O(4) (M = Co, Ni, Mn, Zn) nanocomposites, have been synthesized via a generalized one-pot route, and these materials prove to be efficient MRCs in the catalytic epoxidation of styrene. Characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared (IR) and X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and magnetic measurement reveal that the nanocomposites are assembled from well crystallized Ag and corresponding ferrite primary particles with the assistance of polyvinylpyrrolidone (PVP). The nanocomposite samples are comparable in Brunauer-Emmett-Teller (BET) specific surface areas and are superparamagnetic at room temperature. The as-prepared MRCs exhibit high activities in the epoxidation of styrene in toluene with tert-butylhydroperoxide (TBHP) as the oxidant and very high yields of styrene oxide can be achieved within 5 h of reaction. All the MRCs can be easily recovered by using a magnet and no decrease in the yield of styrene oxide has been observed after several consecutive rounds of reaction. It has been demonstrated that the ferrite supports affect the structure of Ag and the efficiency in oxygen supply and thus the catalytic performance.