Fe-ZSM5 catalysts were prepared at room temperature. Iron was incorporated into H-ZSM5 in organic media (toluene) using iron acetyl acetonate. In order to elucidate the catalytic performance of this Fe-ZSM5, reference catalysts were prepared by chemical vapour deposition (CVD) and impregnation in aqueous media (IMW). The various catalysts were characterized structurally and morphologically. Materials prepared in organic media and CVD showed fibrous iron particles, with radius between 10 and 40 angstrom, highly dispersed on the external zeolite surface. Fractal dimension values suggest that iron particles grow dendritically when iron is incorporated into zeolite by impregnation in organic media. Nuclear magnetic resonance of Xe-129 adsorbed on catalysts shows that dendrites can penetrate into the zeolite channels. The dispersion of the iron species on the external surface of the zeolite and the presence of iron inside the channels explain the good catalytic performance in the Selective Catalytic Reduction (SCR) of NO. Ammonia and n-decane were employed as reducing agents. The highest NO to N-2 conversion (approximate to 100% at 430 degrees C) was obtained when ammonia was used. In contrast, n-decane is unable to reach Fe species in channels, and the inner active surface is thus lost.