Pd-Y- and Pd-Zr-Y-zeolite catalysts were prepared by the ion-exchange of parent NH3-Y-zeolite, thermally pre-treated Y-zeolite and hydrothermally pre-treated Y-zeolite. The activity of the catalysts was studied in conversion of gas mixtures simulating the flue gases from the combustion of biofuels and natural gas driven vehicles (NGVs) at temperature ranges of 120-800 degreesC. The effect of sulphur-poisoning was examined by the addition of 5 ppm SO2 into the feed gas mixtures. High activity in the removal of the model pollutants was obtained over the fresh catalysts. De-activation was observed as a result of catalyst ageing in the reactants' flow (800degreesC, 6h) or steam treatment (850degreesC, 12 vol.% H2O, 16h). The de-activation was attributed to the de-alumination as well as to the migration of Pd2+ cations. The catalysts were characterised by XRD, SEM-EDXA, N-2-physisorption, O-2/SO2/NH3/naphthalene-TPD, XRF and DCP.