3-WAY CATALYSTS IN A HYBRID DRIVE SYSTEM .1. EXPERIMENTAL-STUDY OF DYNAMIC BEHAVIOR

The suitability of nonpromoted and ceria-promoted Pt-Rh/Al2O3 catalysts 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 tests indicate that ceria-promoted Pt-Rh/Al2O3 is more suitable for these operating conditions. With the ceria-containing catalyst lambda-cycling frequencies up to 3 times lower could be used without any loss of performance. The benefits of lambda-cycling were higher C3H8 and NO(x) conversions and lower N2O production at temperatures below 350-degrees-C. Exposure of both catalysts to air, as occurs during engine startup (filling of cylinder with air), resulted in low NO(x) and C3H8 conversions which were maintained under subsequent stoichiometric operation. Conversions were only improved after exposure of the oxygen-loaded catalyst to a fuel-rich exhaust gas.