The effect of the palladium precursor on the CO and NO adsorption capacity of Pd–MoO 3 /Al 2 O 3 catalysts was studied. TPR and IR analysis showed that the palladium addition promoted the reduction of Mo 6+ to Mo 4+ . The presence of a higher amount of molybdenum oxide partially reduced improved the NO dissociation to N 2 and N 2 O on Pd–Mo/Al 2 O 3 catalysts. This behavior was attributed to the formation of a lower fraction of inactive adsorbed nitrogen species on molybdenum oxide partially reduced. The catalytic behavior of the Pd–Mo/Al 2 O 3 catalysts on the NO+CO reaction could be explained by a bifunctional mechanism. After adsorption and dissociation of NO on Mo 4+ , the oxygen dissociated is transferred to the Pd. The CO adsorbed on the Pd surface reacts to CO 2 .