The mechanism of the CO2 reforming of methane reaction over the Pt/ZrO2 catalyst was investigated using a temporal analysis of products (TAP) reactor system. For comparative purposes, the reaction pathway using a Pt/Al2O3 catalyst was also examined. A reaction sequence is suggested for both catalysts. Over both catalysts, methane decomposition takes place over platinum. The main difference between the two catalysts concerns the carbon dioxide dissociation. Over Pt/Al2O3 this step is assisted by hydrogen. Over Pt/ZrO2 this step takes place over the zirconia support and involves surface vacancies. Moreover, large pools of formate and carbonate species are present on the zirconia. Transient studies conducted to determine the origin of carbon species accumulated during CO2 reforming revealed that more than 99% of the carbon was derived from the methane molecule over both catalysts. Over the Pt/ZrO2 catalyst, only a single very reactive carbon species was detected, while over the Pt/Al2O3 a second less active species was also formed. (c) 2006 Elsevier B.V. All rights reserved.