Catalysts based on Na-mordenite (symbolized as 'M') exchanged with 5, 10 and 15 wt. % of Ag were characterized by XPS, EXAFS, XANES and UV-Vis DRS spectroscopic techniques in order to investigate the effect of different treatments on the chemical state and surface concentration of silver species. The Ag x M catalysts were analyzed in oxidizing (O 2 ) or reducing (H 2 /Ar) atmospheres and also after being used in the selective catalytic reduction of NOx or in successive cycles of toluene adsorption/desorption.In calcined samples, EXAFS profiles showed two types of Ag-O spheres of coordination, one due to a dispersed phase of silver oxide and the other, to Ag + ions in interaction with the oxygen of the zeolite framework. The UV-Vis DRS spectra showed the coexistence of isolated Ag + , Ag n δ+ (n < 10) cationic clusters and Ag x O particles. In addition, through the modified Auger parameter (α'), calculated from XPS measurements, it was possible to identify Ag + ions at exchange sites (α'~722 eV) and Ag x O (α'~725 eV) highly dispersed on the surface. Both species constitute stable active centers for the SCR of NOx under severe reaction conditions. However, during the adsorption-desorption of toluene, the reduction of silver oxides produces Ag(0) due to thermal hydrocarbon decomposition.