The influence of the support and the presence of oxygen were investigated in the steam reforming of acetic acid, a bio-oil model compound, over Pt/ZrO2 and Pt/CeO2 catalysts. In the absence of oxygen, all catalysts suffered from deactivation. Acetone, formed via condensation/dehydration of acetic acid, is a coke precursor and causes catalyst deactivation. The use of a support with red-ox properties and the presence of oxygen improved the stability of the Pt/CeO2 catalyst tremendously. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) characterization of coke indicates that the presence of oxygen prevents extensive oligomerization/coke forming reactions and that the resulting specie are more easily combusted. (C) 2009 Elsevier B.V. All rights reserved.