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On a global basis there is a resurgence of interest in the use of palladium in automotive emission control catalysts because of cost, availability and performance advan­tages under certain operating con­ditions relative to more expensive noble metals. This paper reviews a variety of potential vehicle applic­ations for the use of palladium containing catalysts. Included in the study are for the replacement of platinum by palladium in conventional platinum/rhodium systems, palladium-only three-way catalysts, palladium-only dual bed catalysts and two-stroke and lean-burn engine applications.

Rhodium supported catalysts capable of withstanding temperatures above 600°C under oxidizing conditions while maintaining a resistance to chemical poisons have been developed by reducing the undesirable interaction of Rh2O3, with γ-alumina support material. The impregnation of Rh on a zirconia (ZrO2) washcoat provides a well dispersed, thermally-stable active phase. When the Rh/ZrO2 phase is in turn supported on a high surface area γ-Al2O3 washcoated monolith, the resulting (Rh/ZrO2)/γ-Al2O3 catalyst also has sufficient surface area for dispersion of other active metals, as well as to provide a sink for fuel-and oil-derived contaminants. Upon heating at 850°C in air, the Rh area is decreased by 95% when supported on γ-Al2O3 but is lowered only by 15% when ZrO2 is used to separate Rh from γ-Al2O3.