We have investigated the effect of supporting rhodium on several different types of graphite nanofibers (GNFs) for the ethylene hydroformylation reaction at temperatures over the range 180-300 degreesC. The performance of these systems was compared with that of a catalyst where the same metal loading was dispersed on silica. It was found that in general, while the activity of all the catalyst systems was similar, the GNF supported rhodium catalysts exhibited a higher selectivity for the formation of propionaldehyde than the corresponding silica supported system. Furthermore, among the various rhodium/GNF catalysts, the ribbon type nanofibers appeared to give the highest selectivity to the desired product. The optimum temperature for the hydroformylation reaction was found to be 240 degreesC, since at this condition one was able to achieve the combination of maximum activity with acceptable selectivity. Based on many experiments in which the ratio of gaseous reactants was systematically varied it was evident that high partial pressures of CO and C2H4, and a concomitant low partial pressure of H-2 gave the optimum performance. It is believed that the morphological characteristics: acquired by rhodium when dispersed on the GNF edges is a critical factor rather than the size of the individual crystallites. (C) 2001 Published by Elsevier Science B.V.