Deactivation of manganese-cerium oxide catalysts during wet oxidation of phenol

The catalytic deep oxidation of phenol in aqueous solution using manganese cerium oxide catalysts was studied by varying catalyst composition, pH of the reactant solution, partial pressure of O-2, reaction temperature and possible intermediates of the reaction. A deactivation of the catalysts was observed. A leaching of cerium-and preferentially of magnesium-into the solution, and formation of carbonaceous species on the surface of the catalysts were observed. It is suggested that deactivation is due principally to the formation of a polymer on the surface of the catalyst during reaction. Modifications of the experimental conditions of the reaction (pH, temperature, pressure) or the composition of the oxides do not prevent this deactivation. Polymer formation seems to be well explained by a mechanism proposed in the literature attributed to a heterogeneous-homogeneous free-radical mechanism. Some lines for future research are proposed.