Catalytic ammonia decomposition has been of increasing interests as a means of supplying pure hydrogen for fuel cells. In this study, Ru catalysts supported on different carbons were used for catalytic ammonia decomposition. The influences of the porous and graphitic structures of carbon supports on the activities of the catalysts were examined. The catalytic activity over supported Ru catalysts is ranked as Ru/GC (graphitic carbon) > Ru/CNTs (carbon nanotube) > Ru/CB-S (carbon black) > Ru/CB-C > Ru/CMK-3 approximate to Ru/AC. The samples are characterized by XRD, N-2 adsorption, Raman spectra and H-2 chemisorption. Ru particles are highly dispersed on carbon supports. The optimum range of Ru particle sizes is around 3-4 nm. On the support side, the graphitic structure of the carbons is critical to the activity of the supported Ru catalyst, while the surface area of carbons is less important. (c) 2007 Elsevier B.V. All rights reserved.