The oxidation of model soot by NO2 and O-2 in the presence of a Ru/Na-Y catalyst under conditions close to automotive exhaust gas after-treatment systems is investigated. Isothermal oxidation experiments of a physical mixture of carbon black and catalyst were performed ill a temperature range of 300-400 degrees C. A remarkable increase of the oxidation rate by NO2 and O-2 in the presence of the Ru/Na-Y catalyst was observed. An overall mechanism involving oxygen transfer from the Ru catalyst to the carbon surface leading to an increase of C(O) complexes is proposed. These C(O) complexes are destabilized in the presence of NO2 increasing the carbon oxidation rate.