Ball milling as an effective method to prepare magnetically recoverable heterometallic catalysts for alcohol oxidation

Heterometallic double Fe2O3–CoCl2, CoCl2–V2O5, MoO3–V2O5, and triple CuO–Fe2O3–CoCl23d metal dispersed systems were easily prepared by ball milling at room temperature and characterized by scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). They catalyze the microwave-assisted solvent-free heterogeneous oxidation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (t-BuOOH) as oxidant, used as a model reaction. In most of the heterometallic systems a significant improvement in the catalytic activity was observed in comparison to homometallic ones. For the tested catalytic systems and experimental conditions, the CuO–Fe2O3–CoCl2and Fe2O3–CoCl2systems exhibit the highest activity with maximum 78% yield and TON 39 after 1 h. The possibility of magnetic recovery of the catalysts was demonstrated for the Fe2O3–CoCl2(3:1) system.