Preparation of gamma-Fe2O3@C@MoO3 core/shell nanocomposites as magnetically recyclable catalysts for efficient and selective epoxidation of olefins

Magnetic gamma-Fe2O3@C@MoO3 core-shell structures were fabricated via a general approach and characterized by several techniques such as XRD, XPS, ICP-AES, Raman etc. The catalytic performance of them has been demonstrated in heterogeneously catalyzed oxidation of cyclooctene with tert-butyl hydroperoxide (tBuOOH) as an oxidant, and high conversion (100%) and selectivity (over 99%) were achieved with relatively low catalyst dosage under mild conditions. It should be emphasized that the hybrid catalyst could be easily separated by an external magnet and reused up to 9 times with no significant loss of activity and selectivity. The reaction mechanism over MoO3 is also discussed on the basis of the FTIR and XPS measurements. It is suggested that the high catalytic activity is related to the formation of the transition state, a Mo-alkyl peroxide and olefin complex, which is beneficial for an efficient oxygen atom transfer by converting the intermolecular process directly into an intramolecular process.