Temperature-programmed self de-coking tests were carried out to study the factors in forming CO and CO2 over Ni-gadolinia-doped ceria (GDC), Fe-GDC, and Ni-Fe-GDC cermet catalysts with relation to direct methane SOFCs. It was found that the bulk lattice oxygen plays a very important role in forming CO and CO2. CO formation is generally associated with 0 species coming from the bulk lattice oxygen while CO2 formation generally is associated with the surface OH species. With Ni:GDC = 3:5 in weight, a very large amount of CO is formed with relatively negligible CO2 formation. With 1 wt% Ni, preferential CO2 formation can be realized below 700 degrees C. The activity of CH4 decomposition over Fe is much lower than that over Ni, but CO, formation is favored over Fe. A large promotion of the CO2 formation activity appears with the addition of 0.1 wt% Fe into 1 wt% Ni and a synergistic effect is demonstrated. In general, CO2 formation is favored below 700 degrees C while CO formation favored above 800 degrees C. However, with Fe addition, CO2 formation can be favored over Ni-GDC at 1000 degrees C due to the high-temperature redox property of the Fe species. Thus, for preferential CO2 formation, highly dispersive Ni distribution with Fe addition is recommended for the anode cermet of intemediate-temperature SOFCs. (c) 2006 Elsevier B.V. All rights reserved.