Durability of palladium automotive catalysts: effects of trace lead levels, exhaust composition, and misfueling

The activity and durability of Pd catalysts were investigated as a function of trace Pb levels in fuel, exhaust composition and misfueling with leaded fuels to determine their potential as automotive emission three-way catalysts. In laboratory durability studies, Pd catalysts showed significant improvement for nitric oxide (NO) and hydrocarbon (HC) conversions as trace Pb levels decreased in the range 12 mg of Pb/gal to Pb-sterile fuel. Lean exhaust gas compositions during catalyst aging significantly improved the performance of the Pd catalyst for NO conversions near stoichiometry, improved HC conversions during rich excursions and substantially lowered HC light-off temp. Results on Pd catalysts of experiments designed to mimic misfueling with Pb levels typical of commercial leaded fuels are discussed. The practical implications of these results toward the design of future automotive emission systems are considered. 22 ref.--AA