The hydrothermal synthesis of Cu-modified ZSM-5 by introducing Cu ions during zeolite synthesis (Cu/ZSM-5 in ) and by conventional impregnation (Cu/ZSM-5 imp ) has been compared. The catalysts were characterized by X-ray diffraction (XRD), FTIR spectroscopy in the T-O-T vibrations rang, scanning electron microscope (SEM), FTIR of pyridine adsorption and N 2 adsorption. They were subjected to FTIR of NO adsorption for evaluating reactivity of Cu species changed with preparation method. The heterogeneous nature of Cu/ZSM-5 imp is stressed with preponderance of CuO particles on the external zeolite surface. Contrary to this result, Cu/ZSM-5 in showed evidence for highly dispersed and isolated Cu 2+ centers in coordination with lattice oxygen of zeolite. Results of NO-FTIR experiments showed a clear performance for direct NO dissociation where Cu/ZSM-5 in is favored over Cu/ZSM-5 imp . This result, however, appears to correlate with the nature of Cu ions in the samples. The tetrahedral geometry of Cu 2+ ions in the lattice of Cu/ZSM-5 in served in a noticeable development of BrΓΆnsted acid sites (BAS) compared with analogies on Cu/ZSM-5 imp . The nitrosyl complexes observed over Cu/ZSM-5 in were N 2 O, NO-Cu 2+ , O-NO Ξ΄+ , NO 2 -and mono-and bidentate NO 3 -. Similar species were observed on Cu/ZSM-5 imp , together with evidence for concurrent appearance of two spectral features due to stable NO 3 -species at 1713 and 1327 cm -1 . When these results are compared with those obtained over parent ZSM-5 and Cu/ZSM-5 in , the latter species is associated mainly with the Cu 2+ ions in discrete CuO phase which led to deactivation of Cu/ZSM-5 imp .