Device for treating exhaust gas of a diesel vehicle including an exhaust purification element

Exhaust gas treatment device for a diesel vehicle exhaust line comprising a filter element (20). In this device, the pollution control conversion element comprises a material for temporary storage of nitrogen oxide NOx on walls (20P) ensuring the treatment of exhaust gases in the pollution control conversion element. This material is configured on the walls of the pollution control conversion element to ensure said temporary storage during a diesel engine cold start phase in lean mixture and to ensure desorption by reduction of nitrogen oxide NOx by the reducing compounds of the exhaust gases in standard operating mode of the diesel engine in stoichiometric mixture. Powertrain assembly for a motor vehicle, comprising a diesel engine and an exhaust line having such an exhaust gas treatment device. Method of operation of such a powertrain assembly.