The formation and stability of surface species generated in the interaction of ethanol and ethanol-water mixture with Al2O3 and CeO2-supported noble metal catalysts were studied by FT-IR, TPD and TPR methods. It was found that water enhanced the stability of ethoxide surface species formed in the dissociation of ethanol. Dehydrogenation of molecularly adsorbed ethanol was proposed as a key reaction step. The TPD spectra of ethanol adsorbed on supported noble metals exhibited a high temperature desorption stage which was explained by the formation and decomposition of surface acetate species. Ethylene (product of the dehydration of ethanol) was mainly formed on Al2O3-supported noble metals, while on CeO2-supported noble metals significant amount of acetaldehyde (originated from the dehydrogenation of ethanol) was also formed. In the steam reforming of ethanol the selectivity of H-2 formation decreased but that of C2H4 increased in time, while the conversions were stable on alumina-supported noble metals. These observations were explained by the inhibiting effect of surface acetate species. (C) 2006 Elsevier B.V. All rights reserved.