The effect of Pd additive on the catalytic performance of Pt/Al2O3 for the total oxidation of a mixture of n-decane and 1-methylnaphthalene as model hydrocarbons was investigated to develop a highly active diesel oxidation catalyst. Bimetallic Pt-Pd diesel oxidation catalyst showed higher catalytic activity for the total oxidation of hydrocarbons even after high temperature ageing than monometallic Pt and Pd catalysts. The optimum Pt/Pd weight ratio was 3/1. Catalyst characterizations such as XRD, CO-TPR and FT-IR spectroscopy following CO adsorption revealed that an enrichment of Pt on the surface of alloyed Pt-Pd particles in PtPd/Al2O3 is responsible for high hydrocarbon oxidation activity. The catalytic activity of PtPd/Al2O3 was also found to be effectively improved by modification of Al2O with 1 wt% WO3 as acidic additives. The role of WO3 additive was considered to create strong Lewis acidic sites by interaction with Al2O3, leading to a stabilization of PtPd sites in highly active metallic state. (C) 2014 Elsevier B.V. All rights reserved.