CO present in H-2 provided as fuel for polymer electrolyte membrane fuel cells (PEMFC) can degrade the electrochemical performance and needs efficient removal, which can be accomplished by CO preferential oxidation (PROX). PROX catalytic activities in a H-2-rich stream were tested and compared using ruthenium (Ru) nanoparticles supported on two different nanotubularly structured materials, carbon nanotubes (CNTs) and halloysite nanotubes (HNTs). In both of the support materials the morphology remains unchanged after Ru deposition and reduction, demonstrating that their tubular structure is thermally-stable. The catalytic results show that the Ru/HNTs perform better than Ru/CNTs at temperatures below about 110 degrees C, owing to the easier reducibility of Ru particles over the former than the latter. However, Ru/HNTs can only reach a maximum CO conversion of 55%, with an O-2 selectivity of around 27% applying an O-2/CO mole ratio = 1 at 123 degrees C, which is insufficient for PROX applications. CNTs, on the other hand, provide larger surface area and have functional groups with stronger interaction with Ru nanoparticles, presenting a better Ru dispersion, which accounts for the superior catalytic activity at higher reaction temperature. Ru/CNTs catalyst exhibits a CO conversion over 90% and O-2 selectivity of around 50% applying the same O-2/CO mole ratio at temperatures above 120 degrees C. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.