The effect of graphitization of carbon nanotubes (CNTs) on the oxidative dehydrogenation of ethylbenzene to styrene was studied. An elimination of functional groups was observed by treating the catalyst under inert gas at temperatures below 1100 degrees C, while its microstructure and reactivity in TPO experiments did not change significantly. A decrease in the initial catalytic performances was observed, but the functional groups can be regenerated during the catalytic reaction, thus leading to a significant improvement in the catalytic activity. Annealing CNTs above 1500 degrees C leads to a well graphitisized wall structure of CNTs with a nearly oxygen-free surface with a low number of defects. The obtained samples show low but stable catalytic performances, indicating that the oxygenated active sites cannot be regenerated on this well-organized and low defective surface. (C) 2009 Elsevier B.V. All rights reserved.