The effect of sodium promoter on cobalt-zinc oxide catalysts was studied. Catalysts with different sodium contents (up to 1% (w/w)) were prepared by a coprecipitation method. They were studied in the steam reforming of ethanol between 523 and 723 K and characterized by transmission electron microscopy, X-ray diffraction, Raman and infrared spectroscopies, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared spectroscopy. A high segregation of sodium on the surface of catalysts took place. The sodium addition had a positive effect on the steam-reforming reaction of ethanol. Under total conversion and in the 623-723 K temperature range, the production of hydrogen from an ethanol-water (C2H5 OH:H2O = 1: 13 molar) mixture (bioethanol) increased (5-8%) with sodium content. In addition, the incorporation of sodium resulted in the stabilization of the catalysts toward deactivation. In particular, the sodium-promoter effect was related to a decrease in carbon deposition, as evidenced by transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. (C) 2003 Elsevier Inc. All rights reserved.