CoO x /ZrO 2 samples, prepared by adsorption from cobalt solutions or by impregnation, were characterized by means of DRS, XPS, FTIR and volumetric CO adsorption. In samples prepared by adsorption the maximum Co-uptake was 2.2 atoms nm - 2 . XPS evidenced cobalt dispersion up to about 2 atoms nm - 2 . DRS evidenced Co 3 O 4 above 2 atoms nm - 2 . Volumetric CO adsorption, combined with FTIR, showed that cobalt was highly dispersed on the ZrO 2 surface in samples containing 0.4 and 0.9 atoms nm - 2 . The selective catalytic reduction (SCR) of NO with C 3 H 6 in the presence of excess O 2 was studied on samples containing up to 4.8 Co atoms nm - 2 with a reactant mixture containing NO=4000ppm, C 3 H 6 =2000ppm, O 2 =2%. Isolated cobalt in CoO x /ZrO 2 containing up to about 2 atoms nm - 2 is active and selective for NO reduction in the presence of excess O 2 . Aggregated cobalt present as Co 3 O 4 in more concentrated samples is active for C 3 H 6 combustion, thus rendering the relevant CoO x /ZrO 2 samples non-selective.