Technical Paper
The Effectiveness of Pd for Converting Hydrocarbons in TWC Catalysts
1993-03-01
930253
The relative effectiveness of Pt and Pd in TWC catalysts for converting hydrocarbon (HC) species was investigated using engine dynamometer and vehicle FTP evaluations. An engine-aged Pd/Rh TWC catalyst showed higher HC conversions in Bag-1 than a comparably aged Pt/Rh TWC catalyst even though light-off activity for the Pt/Rh was approximately 40 °C lower than for the Pd/Rh. Analysis of the Bag-1 HC species by capillary gas-chromatography suggested that Pd was more effective in oxidizing both C2-C5 paraffins and aromatic HCs. In Bag-2 and -3, where Pd/Rh HC conversions were lower than those of the Pt/Rh, the Pd/Rh was superior to the Pt/Rh in converting the aromatic HCs. A Pt/Rh at the front (upstream location) and the Pd/Rh at the rear position was found effective for lowering HC emissions in comparison to the Pt/Rh-Pt/Rh converter system while maintaining CO and NOx conversion performances.
