15 N nuclear magnetic resonance studies of the NO–O 2 –NH 3 reaction over ZSM-5 zeolites

15 N nuclear magnetic resonance spectra produced by adsorption on ZSM-5 zeolites of NO alone or together with O2 and NH3 have been examined. N2 and N2O as products of NO disproportionation were identified by their 15N NMR spectra. Cationic and acidic centres were suggested to be responsible for the catalytic activity of zeolites in this reaction. The 14N–15N isotopic exchange between reaction components indicates the formation of the intermediate complexes between NH3 and NxOy· M+ species in the adsorbed state.