Partial oxidation of cyclohexane with reductively activated dioxygen on SmCl3 supported on graphite during H2–O2 fuel cell reactions

Abstract

The oxidation of cyclohexane to cyclohexanol (CyOH) and cyclohexanone (CyO) on SmCl₃ supported on graphite (SmCl₃/Gr) utilizing an H₂–O₂ fuel cell system has been studied by means of kinetic and electrochemical techniques. O₂ is reductively activated on SmCl₃/Gr with e^– and H⁺ which are supplied from the anode. The kinetic and electrochemical results have suggested that the current is determined by the electrochemical reduction of O₂, but the oxygenate formation depends strongly on the stationary concentration of active oxygen (O*) generated on SmCl₃/Gr. The optimum rate of formation of the products was obtained at a cathode potential of –0.24 V (vs. Ag|AgCl). The active site on SmCl₃/Gr was suggested to be a Sm³⁺ coordinated with surface functional groups on the graphite. The reaction between the O* and cyclohexane proceeds through a non-electrochemical reaction and produces CyOH and CyO in parallel. The selectivity of the products on SmCl₃/Gr did not change appreciably under different cathode potentials and O₂ pressures. However, the selectivity varied widely for the oxidation on FeCl₃/Gr. These observations suggest different O* species between SmCl₃/Gr and FeCl₃/Gr.