Synthesis of caprolactone by the oxidation of cyclohexanone over composite Mg-Fe oxide catalysts

Composite Mg-Fe oxides were prepared from magnesium nitrate and ferric nitrate via coprecipitation and were characterized by means of XRD, N₂ adsorption-desorption and CO₂-TPD. Their catalytic performances in the oxidation of cyclohexanone to caprolactone with molecular oxygen were investigated. The XRD results indicated that magnesium ferrite formed in the composite oxides, which led to the bigger specific surface area and porous volume. When the mole ratio of MgO to Fe₂O₃ was 4, the prepared Mg-Fe-4 catalyst showed the highest catalytic performance among the prepared catalysts due to its appropriate specific surface area, porous volume and basicity. The influences of various reaction conditions on the catalytic performances of the Mg-Fe-4 catalyst were discussed. Under the conditions of mass ratio of Mg-Fe-4 to cyclohexanone 0.26, mass ratio of pro-oxygenic agent benzaldehyde to cyclohexanone 2.6, mass ratio of acetonitrile to cyclohexanone 25, initial O₂ pressure 1.0 MPa, reaction temperature 80℃ and reaction time 6 h, the conversion of cyclohexanone and the selectivity to caprolactone reached 92.8% and 91.4%, respectively.