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The deactivation of automotive catalysts by engine oil-derived components of phosphorus and zinc can occur by the formation of an amorphous zinc pyrophosphate (Zn2P2O7) that is impervious to gas diffusion. The catalyst poison, derived from antiwear oil additive zinc dialkyl dithiophosphate (ZDP) in low-temperature exhaust environments, appears as glassy, amorphous deposits on catalysts as shown by scanning electron microscopy (SEM). Laboratory studies were performed to understand the effects of exhaust stoichiometry, temperature, rate of oil burn, and chemical form of P and Zn compounds on glaze formation. The formation of the amorphous deposits using a laboratory pulsator apparatus showed that noncombusted ZDP causes the glaze formation. Electron microprobe studies indicated the association of P with Zn on precious metal films exposed to ZDP combustion products. Secondary ion mass spectrometry (SIMS) confirmed a similar P to Zn correspondence on the vehicle-aged catalysts.

The thermal deactivation of current automotive three-way catalysts (TWCs) was studied under various high temperature conditions to determine which were most damaging. The catalysts were aged on an engine dynamometer simulating the U.S. emission durability cycle with additional periodic exposure to high temperatures. The deactivation was measured as a function of the duration, temperature and air-fuel ratio during the high temperature exposure. With lean air-fuel ratios during the high temperature exposure, TWC performance as measured at 600 F was most susceptible to deactivation showing appreciable loss of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) conversions after 20 minutes of aging at 1600 F. The TWC performance as measured at 800 F had comparable loss only after 60 minutes of aging at 2200 F. With rich air-fuel ratios the TWC performance remained nearly unaffected by aging up to 2000 F, but it dropped substantially after aging at 2200 F.

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.

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.

A copper chromite ZrO2 honeycomb catalyst has been evaluated in the laboratory and to a limited extent on vehicles. When 650-850 grams of this catalyst (1.4-1.9 lbs) is dispersed on two honeycombs and used to catalytically treat the exhaust of a 4500 lb, 400 in3 Torino, the percent oxidation of CO and hydrocarbons during the Federal Test Procedure are close to, but less than that produced by present noble metal production catalysts. The total active catalyst surface area available with copper chromite ZrO2 catalyst is somewhat marginal and this leads to pronounced susceptibility to lead deactivation during durability even at very low lead levels if the peak catalyst operating temperature is high (900°C). It is desirable to operate below 700-750°C.

The sulfur dioxide to sulfur trioxide conversion has been measured for three different automotive exhaust catalysts. Two of the catalysts were 1975 production catalysts (Engelhard IIB and Matthey-Bishop 3C) and the third is a palladium catalyst on a monolith support. The carbon monoxide and propylene conversions were also measured so that the activity of the three catalysts for these gases could be compared to their sulfur dioxide activity. The measurements were made using a flow reactor with simulated exhaust gas and show that, while the carbon monoxide and propylene conversions were very similar for all three catalysts, there was a wide range of sulfur dioxide conversions. At 525°C and 73,000 hr-1 space velocity the sulfur dioxide conversion was 70% for the Engelhard IIB, 40% for the Matthey-Bishop 3C and from 25 to 70% for the palladium catalyst. The palladium catalyst has a range of conversions under these conditions which are associated with different states of the catalyst.