Behavior of Non-Promoted and Ceria-Promoted Pt/Rh and Pd/Rh Three-Way Catalysts under Steady State and Dynamic Operation of Hybrid Vehicles

Abstract

The suitability of newly developed non-promoted and ceria-promoted palladium−rhodium automotive catalysts for the exhaust gas control of a hybrid drive system has been tested by light-off experiments with steady and cycling feed stoichiometry, and pulsed-flow operation. The dynamic behavior of the honeycomb-type catalysts has been compared to the performance of standard honeycomb platinum−rhodium catalysts. Light-off tests carried out in the range 150−500 °C indicated significant differences in the conversion of NOx, CO, and hydrocarbons during warm-up, depending on the catalyst composition and whether λ-cycling was applied or not. Appropriate λ-cycling substantially improved the behavior of all catalysts in the lower light-off region. At higher temperatures cycling afforded lower conversions of all target components. Under pulsed-flow operation with an air pulse preceding the exhaust pulse (filling of the cylinder with air), asymmetric λ-cycling with longer rich half-cycles resulted in CO and HC conversions as well as N2 yields similar to or higher than those without an air pulse for the ceria-promoted catalysts. The catalytic tests suggest that ceria-promoted palladium is competitive to Pt−Rh−Ce in a hybrid vehicle application.