FeOx/ZrO2 samples, prepared by impregnation with Fe(NO3)(3), were characterised by means of DRS, XRD, FTIR, redox cycles and volumetric CO adsorption. Volumetric CO adsorption, combined with FTIR, showed that 45% of iron in the sample containing 2.8 Fe atoms nm(-2) was capable of forming iron carbonyls. DRS evidenced Fe2O3 on samples with Fe-content greater than or equal to 2.8 atoms nm(-2). The selective catalytic reduction of NO with C3H6 in the presence of O-2 was studied with a reactant mixture containing NO = 4000 ppm, C3H6 = 4000 ppm, O-2 = 2%. The dependence on iron-content suggests that only isolated iron, prevailing in dilute FeOx/ZrO2, is active for NO reduction, whereas iron on the surface of small oxide particles, prevailing in concentrated FeOx/ZrO2, is active for C3H6 combustion.