The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO3/Al2O3 catalyst than on the Pd/CeO2/Al2O3 and Pd/Nb2O5/Al2O3 catalysts. The explanation for the very high N-2 production on Pd-Mo catalyst. during the TPD analysis may be attributed to the NO + Medelta+ stoichiometric reaction. The promoting effect of a reducible oxide for the NO + CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N-2 selectivity.