Abstract The effects of additives, CeO 2 and K 2O, on Pd/Al 2O 3 for CO and C 3H 6 oxidation under oxygen-deficient conditions were investigated. The unpromoted Pd/Al 2O 3 exhibits the highest C 3H 6 conversion among the Pd catalysts, but its CO conversion is very low and even negative at the higher temperature (>500°C). Nevertheless, the CO conversion on Pd/Al 2O 3 can be significantly promoted by the addition of CeO 2 and K 2O. When water participates in the reaction, the CO conversions on the promoted Pd/Al 2O 3 catalysts can be further increased. The promotional extent of CO conversion on the Pd catalysts is in the order: Pd-K 2O-CeO 2/Al 2O 3>Pd-K 2O/Al 2O 3>Pd-CeO 2/Al 2O 3>Pd/Al 2O 3. Moreover, Pd-K 2O-CeO 2/Al 2O 3 exhibits the highest CO conversion among the Pd catalysts. In addition, the test results of the monolithic catalysts also reveal that the CO conversion on PdRh/K 2O/Al 2O 3-CeO 2 is quite close to that on PtRh/Al 2O 3-CeO 2 under the simulative gases and the ECE-40 mode driving cycle test. However, PdRh/K 2O/Al 2O 3-CeO 2 exhibits lower HC conversion due to the lower activity for alkane oxidation.