The conversion of methylcyclohexane (MCH), n-hexane (nH) or a 1/1 mixture of the two hydrocarbons was studied over alumina-supported Pt, Ir and Ru catalysts with metal dispersions varying from 10 to 100%, and prepared from the acetylacetonate precursors. The reaction was carried out between 410 and 650 K. The conversion of nH is strongly inhibited in the presence of MCH, which remains the most abundant reactant adsorbed on the metal particles. Neither the activity, nor the selectivity for MCH conversion, were modified by the presence of nH in the feed. During MCH conversion, the dehydrogenation to toluene is the only reaction observed on Pt catalysts. On Ir and Ru catalysts, ring opening and deep hydrogenolysis to lower alkanes operate, the extent of which depends on the metal and the size of the particles.