The activity and resistance to leaching of a co-precipitated CuCeOx (Cu-at:Ce-at = 1:9; Tc, 500 and 800degreesC) catalyst in the wet oxidation (CWO) of phenol (T-R, 150degreesC; P-R, 12 atm), with reference to a CuZnAlOx commercial system, has been investigated using a semi-batch "slurry" reactor with continuous feeding of oxygen. The role of homogeneous catalysis by leached Cu2+ ions on the activity pattern of solid catalysts is addressed. Thermal and chemical ("acid washing") treatments of the CuCeOx catalyst induce marked modifications on the structure and redox properties also altering its CWO activity-selectivity pattern. The whole set of experimental findings leads to infer that the CWO of phenol on Cu-based catalysts proceeds via a homogeneous-heterogeneous path promoted by the leaching of Cu2+ ions. (C) 2003 Elsevier Science B.V. All rights reserved.