This study focuses on the behaviour of the diesel oxidation catalyst in order to improve the efficiency of an ammonia SCR system on an after-treatment line composed by a DOC + DPF + SCR. The studied catalyst is a commercial diesel oxidation catalyst (Pt/Pd/Al2O3) provided by Renault. For this study, the catalytic phase was extracted from a monolith and different ageings in temperature were performed. The catalysts were characterized by elementary analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled by EDS and X-ray photoelectrons spectroscopy (XPS). The specific surface area was also calculated using a specific apparatus. Main physicochemical properties and elementary analysis of the catalysts were performed in order to determine the noble metal contents. The catalytic measurements consisted on temperature programmed surface reaction (TPSR). The heating rate was chosen equal to 10 degrees C min(-1). The TPSR were used to determine light off temperature of each pollutant present in the exhaust gases. To be close to industrial conditions, our experimental setup is composed by a heater where the gases are heated up to 500 degrees C. The goal of this study is to study the hysteresis effect with different gas composition and with different catalysts state (ageing, sample/powder). (c) 2012 Elsevier B.V. All rights reserved.