Oxidation Mechanism of Normal Paraffin Catalyzed by Cobalt Ion Supported on Active Carbon

Abstract

  It was found that cobalt(III) ion supported on active carbon (Co³⁺/C) was highly active for the oxidation of normal paraffin at 120°C. Results by atomic absorption/flame spectrophotometry showed that cobalt ion supported on active carbon was insoluble in the reaction mixture. Cobalt(III) acetate was catalytically inactive for the oxidation in water or acetic acid used for impregnation. Cobalt(II) acetate supported on active carbon showed no catalytic activity even at 140°C for the oxidation. These results suggest that the oxidation is not catalyzed by residual solution of cobalt(III) ion in the pore of active carbon but that it is catalyzed by cobalt(III) ion supported on the active carbon.
   In order to elucidate the reaction mechanism, the oxidation catalyzed by Co³⁺/C was studied kineticaly. The oxidation rate was one-half order with respect to the cobalt(III) ion concentration and was independent of oxygen pressure. The apparent activation energy was 17 kcal/mol over the temperature range 107-130°C. The fraction of fatty acids, esters, ketones and alcohols in the product was 3: 3: 3: 1 in molar ratio. These results can be explained by the reaction mechanism which has been proposed for the homogeneous oxidation with metal ions. This suggests that the oxidation mechanism over Co³⁺/C is similar to that of the homogeneous oxidation with cobalt ion. Therefore, the active site of the catalyst was concluded to be cobalt(III) ion on active carbon.