The partial oxidation of methane over supported (ZrO2, CeO2-ZrO2) rhodium catalysts was investigated at atmospheric pressure. The effect of temperature, CH4/O-2 ratio, catalyst composition and pre-treatment was studied. Ceria doping of the support material resulted in significant improvements concerning the methane conversion and syngas selectivity, which could be related to a higher noble metal dispersion on the Rh/CeO2-ZrO2 catalyst. In addition, the light-off temperature was decreased by 128 degrees C when using CeO2-ZrO2, as support. X-ray photoelectron spectroscopy revealed the presence of different Rh oxidation states depending on catalyst composition and pre-treatment. A stabilization of partially oxidized (Rh delta+) species by ceria could be detected. An active and stable catalyst behavior could be observed for Rh/CeO2-ZrO2, irrespectively of catalyst pre-treatment, whereas an activation period was required for stabilizing the activity of the Rh/ZrO2 catalyst. The activity tests indicate that the indirect reaction mechanism, consisting of methane combustion followed by steam and dry reforming, prevails under the experimental conditions studied. (c) 2007 Elsevier B.V. All rights reserved.