Catalytic activity and CO2 selectivity over carbon black-supported Pd with the addition of Zn (Zn-Pd/C) was comparable to those of Pd/ZnO in methanol steam reforming. From the characterization of fresh Zn-Pd/C after H-2 reduction pretreatment by means of BET surface area, XRD, TEM and the measurement of CO adsorption, Pd-Zn alloy particles were detected on Zn-Pd/C. This is also supported by high CO2 selectivity in methanol steam reforming over Zn-Pd/C as well as Pd/ZnO. In addition, Zn-Pd/C exhibited higher stability than Pd/ZnO in methanol steam reforming. After the reaction for the life test, the formation of zinc carbonate hydroxide such as Zn4CO3(OH)(6) . H2O was clearly observed on Pd/ZnO. It is expected that the deactivation is caused by covering active Pd-Zn alloy particles with zinc carbonate hydroxide. Although this phenomenon can also occur on Zn-Pd/C, the deactivation rate was much lower than Pd/ZnO because the amount of free ZnO is much smaller on Zn-Pd/C. (C) 2004 Elsevier B.V. All rights reserved.