1994-03-01

Performance and Durability of Palladium Only Metallic Three-Way Catalyst 940935

The paper introduces a new catalytic formulation to improve the performance of 3-way catalyst. This new palladium-only catalyst concept (K4) was designed specifically for low temperature light-off and high temperature applications.The catalysts employed in this study were prepared on metallic substrates of nominal cell density of 78 cells/cm2 (cpscm). To assess the effect of the cell density on the performance, the cell densities of 47 - 186 cpscm were also used.The catalysts were evaluated after the engine dynamometer aging and the on-road aging for 80.000 km. Several physical and chemical methods were used to analyse the washcoat layer. The elements and distribution of the poisons in the catalyst were analysed. The catalytic activities of both fresh and aged samples were measured also in laboratory tests.Pd-only K4 three-way washcoat technology is proved to exhibit superior hydrocarbon conversions compared to the usual Pt-Rh catalysts in extensive dynamometer and vehicle aging studies. Only the NOx efficiency was lower than that of Pt-Rh 3-way converters. The performance of the K4 catalyst can further be optimized by calibrating the lambda-control system exactly for this washcoat chemistry.

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