A non-thermal plasma (NTP) reactor was coupled with a three-function catalyst in order to verify the nature of the effect of the plasma on the catalytic process. A mixture of NO/O2/hydrocarbons in N2 was used as a lean model exhaust gas composition. The plasma was found to perform two of the three functions defined in the catalysis model when coupling the plasma reactor to the catalytic deNOx: NO oxidation to NO2 and hydrocarbon activation through the partial oxidation to aldehyde and/or alcohol were observed. The NOx conversion is higher than 20% between 200 and 360°C, 40% being obtained at 300°C. This behaviour clearly demonstrates the role of the NTP as a promoter of the deNOx reaction which is in full accordance with the proposed model. It can be seen that the NTP is activating the lowtemperature deNOx function of alumina while providing a wide operating temperature window for deNOx reaction.