Catalytic wet oxidation carried out in a continual three-phase trickle-bed reactor contributes to the sustainability of chemical technology. It was found that the hydrodynamics and the mass-transfer or reactants could have a significant impact on the performance of the tickle-bed reactor, An aqueous phenol oxidation was tested at different temperatures and Liquid feed rates and thc activities of both the CuO-supported catalyst and the extruded active carbon were compared. To avoid the impact of liquid maldistribution, a bed of catalyst particles diluted with fine glass spheres was also used. Rate-limited conditions of both liquid- and,eas-phase presented reactants were determined. Under the conditions of gas component transfer limitation, a better wetting of the diluted catalyst bed can lead to a worsening in the reactor performance due to the lower overall reaction rates.