A preferential oxidation reactor (PrOx) is provided including a plurality
of substrates defining a plurality of channels, through which a reformate
stream flows. A CO-sorption layer and a CO-catalyst layer coat a surface
of each substrate support member. The PrOx operates in a first mode,
generally at a temperature below 100 .degree. C., whereby the CO-sorption
material adsorbs CO from the reformate stream. After operation in the
first mode, the PrOx operates in a second mode, generally at a
temperature above 100.degree. C., whereby the CO-catalyst material
enables a preferential oxidation reaction of CO in the reformate stream
with a supply of oxygen and desorption of the CO previously absorbed by
the CO-sorption layer for an overall reduction in the CO content of the
reformate stream.