Development of Thermal-Resistant Rhodium Catalysts 800843
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. The (Rh/ZrO2)/γ-Al2O3 catalyst maintains significant nitric oxide, carbon monoxide, and hydrocarbon activity after thermal treatment at 1100°C in air, while under identical conditions the Rh/γ-Al2O3 catalyst is severely deactivated. The (Rh/ZrO2)/γ-Al2O3 catalyst maintains substantially better durability than Rh/γ-Al2O3 in a simulated exhaust environment at peak temperatures of 950°C with excess oxygen. At comparable surface areas, the (Rh/ZrO2)/γ-Al2O3, catalyst is as resistant to lead poisoning as Rh/γ-Al2O3, and both are more durable than Rh supported on low surface area α-Al2O3.