Ru loaded zirconia catalysts (Ru/ZrO2) were found to be active in the catalytic wet air oxidation (CWAO) of 2-chlorophenol (2-CP) at relatively mild temperature. To optimize the reaction conditions, the effects of different operating parameters, such as the rotation speed, the reaction temperature, the total pressure, the initial concentration and the pH of the initial 2-CP solution on the catalytic activity of 3 wt.% Ru/ZrO2 were evaluated. The activation energy for the CWAO of 2-CP over Ru/ZrO2 was calculated to be 36 kJ mol(-1). The 2-CP removal rate is zero order with respect to the initial 2-CP concentration. The CWAO of 2-CP changes from first order (oxygen diffusion control) to zero order (kinetic control) with respect to the oxygen partial pressure when the total pressure is higher than 4 MPa. The conversion of 2-CP increases with the pH of the initial 2-CP solution. The dechlorination reaction is promoted at higher pH. However, too high pH limits the total mineralization of 2-CP because the adsorption of the reaction intermediates is hindered. It was also confirmed that Ru(NO)(NO3)(3) is better than RuCl3 to act as a ruthenium precursor. (C) 2006 Elsevier B.V. All rights reserved.