Effect of additives on Pd/Al₂O₃ for CO and propylene oxidation at oxygen-deficient conditions

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°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.