Steam reforming of ethanol over an Ir/CeO2 catalyst has been studied with regard to the reaction mechanism and the stability of the catalyst. it was found that ethanol dehydrogenation to acetaldehyde was the primary reaction, and acetaldehyde was then decomposed to methane and CO and/or converted to acetone at low temperatures. Methane was further reformed to H-2 and CO, and acetone was directly converted into H-2 and CO2. Addition of CO, CO2, and CH4 to the water/ethanol mixture proved that steam reforming of methane and the water gas shift were the major reactions at high temperatures. The Ir/CeO2 catalyst displayed rather stable performance in the steam reforming of ethanol at 650 degrees C even with a stoichiometric feed composition of water/ethanol, and the effluent gas composition remained constant for 300 h on-stream. The CeO2 in the catalyst prevented the highly dispersed Ir particles from sintering and facilitated coke gasification through strong Ir-CeO2 interaction. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.