Biomass is probably the only realistic green and sustainable carbonaceous alternative to fossil fuels. By degradation and fermentation, it can be converted into bioethanol, which is a chemical with a range of possible applications. In this study, the catalytic steam-reforming of ethanol for the production of hydrogen is investigated, along with quantitative and qualitative determinations of carbon formation on the catalysts by TPO and TEM experiments. A Ru/MgAl₂O₄ catalyst, a Ni/MgAl₂O₄ catalyst as well as Ag- and K-promoted Ni/MgAl₂O₄ catalysts were studied. The operating temperature was between 673 and 873 K, and a 25 vol% ethanol–water mixture was employed. Deactivation of the catalysts by carbon formation is the main obstacle for industrial use of this process. Carbon formation was found to be highly affected by the operating temperature and the choice of catalyst. The effect of Ag addition was a rapid deactivation of the catalyst due to an enhanced gum carbon formation on the Ni crystals. Contrary to this, the effect of K addition was a prolonged resistance against carbon formation and therefore against deactivation. The Ru catalyst operates better than all the Ni catalysts, especially at lower temperatures.