Effect of K₂O on a Pd-Containing Catalytic Converter for Removing CO and HC Emissions from a Two-Stroke Motorcycle

Noble metals (Pt, Pd, and Eh) supported on Al₂O₃, K₂O/Al₂O₃, CeO₂/Al₂O₃, and K₂O/CeO₂/Al₂O₃ were prepared and characterized with respect to surface area, pore volume, and temperature- programmed desorption of CO₂. The effects of K₂O on the noble-metal catalysts for carbon monoxide and hydrocarbon oxidation were investigated. The reactions were carried out under the stoichiometric and oxygen-deficient conditions. Under the stoichiometric point, the Pd- containing catalysts exhibit higher activity than the Pt-containing catalysts for both CO and C₃H₆ oxidation. Moreover, Pd/K₂O/CeO₂/Al₂O₃ is the most active catalyst among the powder catalysts in this study. Under the oxygen-deficient conditions and in the presence of water, the CO conversions on Pd/Al₂O₃ and Pd/CeO₂/Al₂O₃ are significantly lower than those on Pt/Al₂O₃ and Pt/CeO₂/Al₂O₃, respectively. In contrast, the Pd-containing catalysts exhibit higher C₃H₆ conversion than the Pt-containing catalysts. However, the CO conversions on the Pd-containing catalysts can be promoted by the addition of K₂O. On the other hand, the test results of the monolithic catalysts revealed 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. PtRh/Al₂O₃-CeO₂ is the typical composition of catalytic converters for two-stroke motorcycles. It infers that PdRh/K₂O/Al₂O₃-CeO₂ is a promising catalytic converter for a two- stroke motorcycle.