The effects of additives, CeO2 and K2O, on Pd/Al2O3 for CO and C3H6 oxidation under oxygen-deficient conditions were investigated. The unpromoted Pd/Al2O3 exhibits the highest C3H6 conversion among the Pd catalysts, but its CO conversion is very low and even negative at the higher temperature (> 500 degrees C). Nevertheless, the CO conversion on Pd/Al2O3 can be significantly promoted by the addition of CeO2 and K2O. When water participates in the reaction, the CO conversions on the promoted Pd/Al2O3 catalysts can be further increased. The promotional extent of CO conversion on the Pd catalysts is in the order: Pd-K2O-CeO2/Al2O3 > Pd-K2O/Al2O3 > Pd-CeO2/Al2O3 > Pd/Al2O3. Moreover, Pd-K2O-CeO2/Al2O3 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/K2O/Al2O3-CeO2 is quite close to that on PtRh/Al2O3-CeO2 under the simulative gases and the ECE-40 mode driving cycle test. However, PdRh/K2O/Al2O3-CeO2 exhibits lower HC conversion due to the lower activity for alkane oxidation. (C) 1998 Elsevier Science B.V. All rights reserved.