The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V2O5/Al2O3 catalysts was investigated. The Pd/V2O5/Al2O3 catalysts were more active than V2O5/Al2O3 and Pd/Al2O3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V4+ species were more active, the Pd particle size effect was responsible for the higher activity. (C) 2004 Published by Elsevier B.V.