Durability of Automotive Catalysts for European Applications

The durability of automotive three-way catalysts (TWCs) for European applications were investigated as a function of higher temperatures encountered in autobahn driving modes over extended periods of time, potentially higher residual lead (Pb) levels anticipated in European marketed unleaded fuels, and occasional misfueling with leaded fuels. In laboratory durability and dynamometer aging studies, platinum-rhodium (Pt-Rh) TWCs at higher loadings than currently used in US applications maintained substantial three-way conversions when aged under rich conditions (λ ∼ 0.9) at maximum temperatures of ∼ 900 to 1000°C with 3 mg Pb/L fuel levels. Increasing maximum catalyst aging temperatures from 730°C to 1000°C resulted in ∼50% reduction in BET surface area which increased stoichiometric hydrocarbon light-off temperatures, but improved net NO and HC conversions after light-off due to lower Pb retention on the TWC. Increasing residual Pb levels in the range from 3 to 10 mg Pb/L when aging in pulse-flame reactors at 1000°C substantially decreased TWC performance, and the TWC was poisoned for saturated hydrocarbon oxidation in <6400 simulated km (4000 mi). Results of experiments designed to simulate occasional misfueling with Pb levels typical of commercial leaded fuels are discussed.