Reduction by CO of NO x species stored onto Pt–K/Al 2O 3 and Pt–Ba/Al 2O 3 lean NO x traps

Abstract

In this paper the results obtained in our previous studies on the reduction of nitrates by CO over Pt–K/Al 2O 3 and Pt–Ba/Al 2O 3 catalysts are compared and discussed in order to define the chemistry that leads to nitrogen evolution during the regeneration of the different lean NO x traps. The reaction mechanisms and pathways leading to N 2 formation under dry conditions are investigated by complementary transient dynamic experiments and FT-IR analyses. In both cases, the reduction of stored NO x by CO occurs according to a Pt catalyzed surface pathway that does not involve the release of NO x 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 NO x to give nitrogen. This is the exclusive route for nitrogen formation.