Conducting polymers, polypyrrole and polyaniline, were used as supports for Pd in order to obtain catalysts with higher performances than a classical Pd/Al2O3 catalyst for application in water treatment. The supports and the catalysts were characterized by elemental analysis, Fourier transformed infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD) and by their activity in nitrite reduction. It was demonstrated that these conducting polymers can be advantageously used as support for noble metals such as palladium. Indeed, the redox properties of these supports allow the deposition of a part of palladium directly in the reduced state and also a direct reduction of nitrite, even if this reduction is not complete. The Pd/polyaniline and Pd/polypyrrole catalysts are much more active than the classical Pd/Al2O3 catalyst with less ammonium ions. These better performances were explained by the redox and ionexchange properties of the conducting polymers allowing the exchange between the hydroxides produced and the dopant anion of the conducting polymer. The ion-exchange property of the polymer depends on its oxidation state which is directly linked to the polymerization conditions and then can be easily modulated. (C) 2007 Elsevier B.V. All rights reserved.