Selective liquid phase oxidation of cyclohexene over magnetic Fe3O4/graphene oxide nanocomposite

Abstract

Magnetic graphene based nanocomposite catalysts were used for the first time in cyclohexene oxidation reaction. Fe3O4 was found to be the active phase of Fe in the catalysts as evident from the XRD analysis of the samples. Presence of graphene as graphene oxide in the nanocomposites is confirmed from FTIR spectral analysis. The distribution of more or less spherical particles of Fe3O4 over the graphene sheets was evident from the TEM photographs. The activity of bare Fe3O4 increased drastically upon graphene incorporation. Maximum conversion of 92% was attained using tert-butyl hydroperoxide as the oxidant over the best nanocomposite catalyst in which Fe3O4 was supported over 2 wt% graphene oxide. Using H2O2, double bond oxidation was the major reaction (78.27% conversion) and 1,2-cyclohexane diol was the major product (87.89% selectivity) under the selected reaction conditions of 0.05 g of catalyst with 5 mL of acetonitrile solvent at 70 °C in the 6 h reaction between 2 mmol of cyclohexene and 10 mmol of oxidant. Catalysts recovery from the reaction mixture was very easy by the use of a magnet that in turn facilitated the effective reusability of the Fe3O4 /graphene nanocomposite. The reused catalyst was characterized using TEM and FTIR spectral analyses and it is found that the partial loss in activity can be a resultant of the oxidation of graphenic C=C and the formation of epoxy linkage and –OH groups in the sheets, which hinders the efficient electron migration during catalysis.