This study shows that the air oxidation treatment of an activated carbon originates drastic changes in its chemical surface composition leading to the formation of a less acidic surface with thermally stable oxygenated groups, mainly hydroxyl and carbonyl groups. The oxidation treatment also induces changes in the textural properties, although less pronounced than the extent of the chemical changes. The degree of oxidation was characterized by temperature programmed desorption (TPD). Pt/AC catalysts were prepared on the activated carbon supports by organometallic chemical vapor deposition (OMCVD). Another set of catalysts was prepared on the same supports by the classical incipient wetness impregnation method. The platinum loading of each sample was kept fixed at 1 wt.%. These Pt/AC catalysts were characterized by H-2 adsorption, temperature programmed reduction (TPR), electron microscopy (TEM), infrared spectroscopy (DRIFTS) and tested for their activity in benzene hydrogenation. The changes in the physical and chemical structures of the activated carbons have pronounced effects on the characteristics of both impregnated and OMCVD samples. The results revealed that the preparation by OMCVD on the air oxidized support leads to a drastic increase in both Pt dispersion and catalytic activity. No pronounced differences were observed between the dispersion and activity of impregnated and OMCVD samples that were prepared on the non-oxidized activated carbon.