Reduction by CO of NOx species stored onto Pt–K/Al2O3 and Pt–Ba/Al2O3 lean NOx traps

In this paper the results obtained in our previous studies on the reduction of nitrates by CO over Pt–K/Al2O3 and Pt–Ba/Al2O3 catalysts are compared and discussed in order to define the chemistry that leads to nitrogen evolution during the regeneration of the different lean NOx traps. The reaction mechanisms and pathways leading to N2 formation under dry conditions are investigated by complementary transient dynamic experiments and FT-IR analyses. In both cases, the reduction of stored NOx by CO occurs according to a Pt catalyzed surface pathway that does not involve the release of NOx in the gas phase as a first step, is effective already at low temperature and leads to nitrogen. The proposed reaction scheme implies the formation of surface isocyanate species followed by their reaction with residual stored NOx to give nitrogen. This is the exclusive route for nitrogen formation.