The reaction pathways of N-2 and N2O formation in the direct decomposition and reduction of NO by NH3 were investigated over a polycrystalline Pt catalyst between 323 and 973 K by transient experiments using the temporal analysis of products (TAP-2) reactor. The interaction between nitric oxide and ammonia was studied in the sequential pulse mode applying (NO)-N-15. Differently labelled nitrogen and nitrous oxide molecules were detected. In both, direct NO decomposition and NH3-NO interaction, N2O formation was most marked between 573 and 673 K, whereas N-2, formation dominated at higher temperatures. An unusual interruption of nitrogen formation in the (NO)-N-15 pulse at 473 K was caused by an inhibiting effect of adsorbed NO species. The detailed analysis of the product distribution at this temperature clearly indicates different reaction pathways leading to the product formation. Nitrogen formation occurs via recombination of nitrogen atoms formed by dissociation of nitric oxide or/and complete dehydrogenation of ammonia. N2O is formed via recombination of adsorbed NO molecules. Additionally, both products are formed via interactions between adsorbed ammonia fragments and nitric oxide. (c) 2006 Elsevier B.V. All rights reserved.