Pathways for N2 and N2O Formation during the Reduction of NO x over Pt–Ba/Al2O3 LNT Catalysts Investigated by Labeling Isotopic Experiments

Mechanistic aspects involved in the formation of N2 and of N2O during the reduction of gas-phase NO and of NO x stored over a model PtBa/Al2O3 NSR catalyst are investigated using unlabeled ammonia and labeled NO. The reduction of the stored NO x species (labeled nitrites and nitrates) with NH3 leads to the selective formation of N2 as a major product and of small amounts of nitrous oxide. Based on the nitrogen isotopic distribution, it appears that N2 formation occurs primarily through the statistical coupling of N-atoms formed by dissociation of NO x - and NH3-related surface intermediates, although an SCR-pathway (involving the coupling of NH3- and NO-derived ad-species) is also likely to occur. It appears as well that the formation of nitrous oxide involves either the coupling of two adsorbed NO molecules or the recombination of an adsorbed NO molecule with an adsorbed NH x fragment.