A series of carbon-supported platinum catalysts with different metallic dispersions (from 0.05 to 0.68) was tested for the n-heptane aromatization reaction. The influence of a basic function (MgO) on the catalytic behaviour was also examined. It is found that, as the metal particle size decreases, the turnover frequency for hydrogenolysis increases, while those for isomerization and aromatization remain unchanged. Moreover, the selectivities for isomerization and hydrogenolysis change with the metal dispersion while that for aromatization remains constant. In addition, no modification in catalytic properties is observed by adding base sites to a Pt/carbon catalyst. These results suggest that aromatization is a structure-insensitive reaction and that it is independent of the other reactions.