Electrochemical and X-ray absorption techniques have been used to determine the influence of complexation processes on the catalytic properties of heat-treated systems composed by the mixture of one polymer and Co acetate. Three non-nitrogenous polymers were studied : poly(methyl vinyl ketone) (PVK), poly(acrylic acid) (PAA); and polystyrene (PE). The catalysts composed by PE and PAA presented very low activity for the O-2 reduction; a maximum of activity was found for the PVK catalyst at 1000 degrees C. XAFS experiments at the Co, N, C, and O K edges showed that complexation between Co ions and the polymer yields a good dispersion of the Co ions and formation of small Co clusters during the thermal treatment. The absence of complexation leads to very poor activity, as in the case of PE and PAA.