Steady-state tracing and transient techniques, as well in situ FTIR spectroscopy have been applied to investigate mechanistic aspects of the reforming reaction of CH4 with CO2 over Rh/Al2O3 catalyst. It is found that surface coverage of active carbon-containing species, which are in the reaction pathway to CO formation, is of the order of 0.2 while the surface coverage of active oxygen-containing species which lead to the formation of CO is very small. Three kinds of carbonaceous species (CxHy,ycongruent to0) are found by TPH and TPO techniques to accumulate on the catalyst surface during reaction. The total as well as the relative quantities of the different species were found to depend on temperature and time of exposure. It was also found, by isotopic experiments, that this carbon mostly originates from the CO2 molecule, while the contribution of CH4 is small. (C) 2003 Elsevier B.V. All rights reserved.