CO preferential oxidation on a novel Ru catalyst greatly improved in activity and selectivity over a wide temperature range by the pre-treatment of H-2 reduction was characterized. The high performance was obtained by increasing the population of surface Ru(0) which improved O-2 activation at low temperatures. Methanation of CO on the catalyst can also contribute to the final CO clean-up from ca. 100 to < 1 ppm at low temperatures where the influence of CO2 methanation can be ignored. (C) 2004 Elsevier B.V. All rights reserved.