IR spectroscopic studies of NH3 and CO adsorption were applied to establish the status of Ag0 and Ag+ in silver loaded zeolites Y and USY. The nature of the silver particles and ions and their dispersion were found to be influenced by the type of support. Application of zeolite USY as support allowed to operate such catalysts at low temperatures with high selectivity to nitrogen (95%). Zeolite USY as support guaranteed a high concentration of uniformly dispersed metallic silver species and Ag+ cations with strong electron acceptor properties. The silver species of defined nature together with the highly acidic centres in AgUSY protected NH4+ ions against oxidation thus high selectivity to nitrogen was observed.