A preferential CO oxidation device consisting of an array of 26 parallel microchannel reactors with each a 5 wt% Cu/CeO2-x catalytic coating was designed for application with a 100 We fuel cell system. The reactor device is able to reduce the carbon monoxide concentration in a realistic reformate gas from 1.5 vol.% to 10 ppm at an inlet oxygen to carbon monoxide ratio of 1.5, a WHSV of 240 L g-1 h-1, and within the temperature range of 230–240 °C. The device outperformes similar reactor designs as presented in the literature