Performance of Palladium Automotive Catalysts

Automotive exhaust catalyst applications usually use various precious metals. The strengths and weaknesses of the various precious metal use strategies have been widely discussed. Recently there is a great interest in the use of palladium because of cost, availability, and performance advantages under certain operating conditions relative to more expensive precious metals.

The main reason why a Pd catalyst is not applied to three-way catalysts is the fact that under reducing conditions Pd has a poor NOx reduction capability because of the self-poisoning of hydrocarbon. We have found that NOx reduction activity is improved by both the periodic operation effect and the addition of lanthana to the Pd catalyst. This paper reviews the performance of Pd catalyst in both engine and simulated exhaust gases under reducing conditions.