Honeycomb Auto Exhaust Catalysts Containing Copper Chromite and Palladium

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. Catalyst operating temperatures greater than 550-600°C are necessary to suppress sulfur deactivation without special operating procedures so that this leaves only a narrow temperature range of operation if the catalyst activity is to be preserved.

Catalysts containing a low level of palladium appear to offer a competitive alternate to the use of a high catalyst loading base metal catalyst. The problem of a limited total active catalyst surface area and susceptibility to lead are still present but other constraints are eased.