An effective Mn-Co mixed oxide catalyst for the solvent-free selective oxidation of cyclohexane with molecular oxygen

• A high effective Mn2Co3Ox catalyst for cyclohexane oxidation was prepared.
• This Mn2Co3Ox catalyst has an excellent stability.
• Surface area and the surface Mn4+/3+ and Co3+ amounts are the key parameters.
• Mn/Co affects its phase constitution, surface area and surface Mn valence state.

Mn-Co mixed oxide (MnaCobOx) catalysts were prepared by the precipitation method, and the effect of Mn/Co (atom) on their structural and catalytic performance for the solvent-free selective oxidation of cyclohexane with oxygen was investigated. The results showed that the atomic ratio of Mn/Co would affect the phase constitution, surface area, surface Mn valence states and the reducibility of the MnaCobOx catalysts. When the atomic ratio of Mn/Co in the catalyst is 0.6, the Mn2Co3Ox catalyst behaved with excellent catalytic activity and stability, which should be attributed to its high specific surface area and the high atomic ratios of (Mn4+ + Mn3+)/Mn and Co3+/Co on its surface. The effects of the preparation conditions for the Mn2Co3Ox catalyst and the reaction conditions on the selective oxidation of cyclohexane over the Mn2Co3Ox catalyst was tested. Under the reaction conditions of 0.5 MPa O2 and 140 °C for 4 h, 10.4% conversion of cyclohexane and 62.0% selectivity to a mixture of cyclohexanone and cyclohexanol (KA oil) were achieved. After this Mn2Co3Ox catalyst was repeatedly used 10 times, the cyclohexane conversion and the selectivity to KA oil had hardly changed.

Mn-Co mixed oxide with Mn/Co mole ratio of 2/3 exhibits the high surface area, the high atomic ratios of (Mn4+ + Mn3+)/Mn and Co3+/Co on its surface, leading to the excellent catalytic activity for the selective oxidation of cyclohexane with oxygen in the solvent-free system.Figure optionsDownload high-quality image (125 K)Download as PowerPoint slide