Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy-decarboxylation (R-n-COOH + O-2 --> Rn-1-COOH +CO2) yielding essentially CO2 (route A). It may also be oxidized after C-C bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO2 (route B). Pt/CeO2 is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via C-C bond splitting is much more marked on Ru/CeO2. The catalyst characterization indicates that both noble metal and CeO2 particles remain stable during the reaction. (C) 2004 Elsevier B.V. All rights reserved.