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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.

Post-mortem analyses of 50,000 mi (80,000 km) vehicle-aged catalysts revealed that the use of 0.125g Mn/gal (33 mg/L) as MMT (methyl-cyclopentadienyl manganese tricarbonyl) significantly reduces phosphorus and zinc retention levels at the catalyst inlets by ~20-fold and ~5-fold, respectively. In subsequent laboratory pulsator experiments the presence of 0.016 to 0.157g Mn (as MMT)/gal (4 to 41 mg/L) isooctane fuel containing a 10-fold excess of ZDP (zinc dialkyldithiophosphate, source of oil P and Zn) similarly reduced the retention of P and Zn on TWCs by proportional amounts, while the TWCs maintained significantly higher 3-way conversions than in the absence of MMT. The combustion of Mn from MMT to very stable Mn3O4 probably serves as a scavenger in the exhaust for transporting away fuel- and oil-derived catalyst poisons such as P, Zn, and Pb. The utility of the laboratory results will require verification in vehicle studies.

Poisoning of a typical platinum-rhodium (Pt-Rh) automotive three-way catalyst (TWC) was determined as a function of lead (Pb), sulfur (S) and phosphorus (P) fuel levels, thermal aging and sulfur dioxide (SO2) content in the evaluation fuel. In laboratory studies catalysts were durability tested in pulse-flame reactors followed by flow-reactor activity measurements. Engine dynamometer-aged catalysts were evaluated on a slave vehicle. For Pt-Rh TWCs the activities for nitric oxide (NO), carbon monoxide (CO) and hydrocarbon (HC) conversions were poisoned by trace levels of 1-6 mg Pb/gal (0.3 - 1.6 g/m3). When the peak temperature in the aging cycle was increased from 730 to 870°C (1346 to 1598°F), the activities improved significantly. In an attempt to mimic the effect on TWCs of misfueling with Pb levels typical of commercially available leaded fuels, TWC activities were severely poisoned.