Selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over Ru-based catalysts. Ru metal loading and crystallite size were shown to affect catalyst activity and selectivity. Even operating at a gas-hourly-space-velocity as high as 13,500 h(-1), a 3% Ru/Al2O3 catalyst with a 34.2 nm crystallite was shown to be capable of reducing CO in a reformate to less than 100 ppm over a wide temperature range front 240 to 280 degrees C, while keeping hydrogen consumption below 10%. We present the effects of metal loading, preparation method, and crystallite size on performance for Ru-based catalysts in the selective methanation of CO in the presence of H-2 and CO2. (C) 2007 Elsevier B.V. All rights reserved.