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A comprehensive laboratory evaluation was carried out on recent three-way catalyst formulations. The evaluation of selectivity characteristics was made in a synthetic exhaust mixture where “window” widths and positions for three-way conversion and their change after durability runs were determined. The durability runs were made in combusted gases from laboratory pulse-flame exhaust generators using both contaminant-free fuel and fuels with 1975 levels of Pb, P and S. A thorough evaluation of the “oxygen-storage” capability of the catalysts was performed and the results correlated with engine dynamometer experiments designed to utilize this property of three-way catalysts which allows a wider A/F ratio tolerance. A new technique which involves intentional modulation of the A/F ratio was found to extend the usefulness of such catalysts.

This is a continuation of our earlier paper on the laboratory evaluation of three-way catalysts, SAE 76201. A number of recent 3-way catalyst formulations were evaluated in a laboratory flow-reactor when fresh, after 25,000 simulated miles on a pulse-flame reactor and after 100 or 200 hours of accelerated AMA dynamometer durability. A comparison was made of the effects of contaminant levels on the performance of pulsator - and dynamometer-aged selected catalysts. The 4-fold decrease in contaminant (lead and phosphorus) levels in 76/77 certification fuel compared with the 75/76 fuel significantly improved the durability of 3-way catalysts. The problems of increased NH3 formation on pulsator - and dynamometer-aged catalysts which contain base-metal oxides as oxygen-storage or water-gas shift components is attributed to S-poisoning. An inverse relationship between NH3 formation and the amount of rhodium on aged 3-way catalysts was noted.