Methanol is considered as a good hydrogen carrier for mobile application of fuel cells. In such systems, the exhaust gas of the anode is a multicomponent gas composed of hydrogen and carbon dioxide as main constituents and methanol, carbon monoxide, and steam as minor species. It is necessary to burn out these gases in order to prevent emissions of combustibles and to increase the overall efficiency of the fuel cell. A study on the characteristics of a catalytic monolith reactor to oxidize such a fuel gas in near-adiabatic conditions is performed. Emissions and reactor wall temperature distributions are measured during the combustion of several fuel gas mixtures corresponding to design and off-design fuel cell conditions, in a large range of excess air ratios. The high surface reactivity and diffusion properties of hydrogen are seen to greatly enhance the combustion of the other species, by bringing the wall at temperatures sometimes greater than the expected adiabatic. Ultralow emissions of carbon monoxi...