NOVELTY - A reactor includes a carbon monoxide (CO)-sorption material coating a portion of substrate and absorbs CO to reduce the CO content of a reformate stream flowing through flow channels when the reactor is operating in a first mode; and a CO-catalyst coating a potion of substrate and enables a preferential oxidation reaction of CO to reduce the CO content of the reformate stream when the reactor is operating in a second mode.    USE - For reducing carbon monoxide content in a reformate stream (claimed) of fuel cell, e.g. proton exchange membrane fuel cell, for electrical vehicular power plants.    ADVANTAGE - The reactor enables quicker light-off during start-up to limit unacceptable levels of CO being released to the fuel cell stack, thus providing a cleaner reformate stream to the fuel stack. It provides easy transition between start-up and normal operation.    DETAILED DESCRIPTION - A reactor includes a support assembly including substrates configured for providing flow channels; carbon monoxide-sorption material coating a portion of each substrate; and a CO-catalyst coating a potion of each substrate. The CO-sorption material is active for adsorbing CO to reduce the CO content of the reformate stream flowing through the flow channels when the reactor is operating in a first mode. The CO-catalyst enables a preferential oxidation reaction of CO to reduce the CO content of the reformate stream when the reactor is operating in a second mode.    An INDEPENDENT CLAIM is also included for treating a reformate stream for reducing a carbon monoxide content by providing a substrate having a CO-sorption material and a CO-catalyst, and in fluid communication with a reformate stream; adsorbing CO from the reformate stream into the CO-sorption material to reduce the CO content during a first mode; and oxidizing CO from the reformate stream with the CO-catalyst to reduce the CO content during a second mode.    DESCRIPTION OF DRAWING(S) - The figure is a partial perspective view of the internal portion of the oxidation reactor.    Internal portion (22)    Substrate (24)    Separator (26)    Flow channel (28, 30)    Substrate surface (32, 34)