Performance of Copper Base Metal Catalysts in Stoichiometric Automotive Exhausts

Durability performance characteristics of copper-containing base metal catalysts and base metal/low noble metal catalysts have been determined in laboratory and engine aging conditions under well controlled stoichiometric closed-loop A/F operation.

Cu-Cr base metal formulations yield significant HC and CO conversions under stoichiometric operation after aging at 620°C, but deteriorate rapidly at high-temperature (750°C inlet) stoichiometric operation. Incorporation of Rh into the base metal formulation substantially improved NOx performance, a major weakness of base metal catalysts. The addition of Cu-Cr base metals substantially improves CO oxidation over Pt, Pd, and Rh catalysts but was accompanied by some loss of HC conversion over Pt and Rh. A Cu-Cr/Pd catalyst, however, also had better HC conversions as well as significantly improved light-off performance when compared to a Pd-only catalyst.

The stoichiometric operating strategy and performance envelope for base metal catalysts were probed in engine dynamometer and vehicle studies. The aged performance of the Cu containing catalysts is significantly lowered by lean A/F preconditioning due probably to sulfur poisoning of Cu at low-temperature lean operating conditions.