Comparative Behaviour of Standard Pt/Rh and of Newly Developed Pd-only and Pd/Rh Three-Way Catalysts under Dynamic Operation of Hybrid Vehicles

摘要

The suitability of newly developed non-promoted and ceria-promoted palladium and palladium-rhodium three-way catalysis for the exhaust gas control of a hybrid drive system has been tested with periodic changes of the feed stoichiometry (lambda-cycling) and pulsed-flow operation. The performance of the catalysts under dynamic operating conditions has been compared to the behaviour of analogue samples based on standard platinum-rhodium-technology. Combined use of mass spectrometry and time-resolved FTIR spectroscopy allowed simultaneous monitoring of the exhaust components. The air plug preceding the exhaust pulse in the intermittent operation of the combustion engine had a crucial impact on the performance of the catalysis. The air pulse transfers the catalyst into a defined state, which corresponds to a fully oxidized surface. Controlled application of appropriate lambda-cycling allows to compensate the negative effect of the air plug and to achieve sufficient conversion of NO_x as well as CO and HC to harmless compounds. For application in the hybrid vehicle, ceria-promoted palladium catalysts proved to be superior to the standard platinum-rhodium technology.