An experimental investigation is performed into the cleanup of CO in hydrogen for proton exchange membrane fuel cell (PEMFC) using Pt/Al2O3 and Ru/Al2O3 catalysts. Additionally, the effects of adding the transition metals Co and Fe to a Ru/Al2O3 catalyst are examined. The results show that as the level of Pt addition is increased, the maximum CO conversion rate is achieved at a lower temperature. With Ru/Al2O3 catalysts, the CO conversion rate increases significantly with increasing Ru addition at temperatures lower than 80 degrees C For both catalysts, the methane yield increases with increasing temperature and increasing noble metal addition. At temperatures in the range of 100-140 degrees C, the CO conversion rate and methane yield of the Pt-and Ru-based preferential oxidation (PROX) reactions are both insensitive to the density of the honeycomb carrier. The CO conversion rate is significantly improved by the addition of Fe at temperatures lower than 160 degrees C and by the addition of Co at temperatures higher than 200 C. Of the two metals, Fe results in a greater reduction of the methane yield at high temperatures. Finally, both catalysts achieve a stable cleanup performance over the course of a 12-h stability test and suppress the CO concentration to an acceptable level for PEMFC applications. (C) 2007 Elsevier B.V. All rights reserved.