CWO of phenol on two differently prepared CuO–CeO2 catalysts

The activity and selectivity of the Ce1−xCuxO2−δ catalysts prepared by co-precipitation and by sol–gel methods were studied in the catalytic wet oxidation (CWO) of phenol at 432 K and at 7.3 bar oxygen partial pressure in a semibatch CST reactor. Both types of catalysts are very stable under hydrothermal reaction conditions at low pH values. It has been found that activity and selectivity increase with the dispersion of copper oxide phase on the cerium oxide. While the Cu content was equal in both types of catalysts, the samples prepared by sol–gel technique are up to four times more active and about 25% more selective toward CO2 formation than the samples prepared by co-precipitation at given reaction conditions. The heterogeneously initiated radical mechanism results in autocatalytic type kinetics. The activity and selectivity depend on the initial concentration of heterogeneously catalytically formed radicals in each subsequent oxidation step. Between these steps the radicals react further on in liquid phase.