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A new laboratory test for measuring catalyst oxygen storage capacity has been developed. The test accurately predicts catalyst performance on the vehicle during transient A/F excursions and correlates well with vehicle CO and Nox tailpipe emissions. The test was subsequently used to facilitate improved oxygen storage capacity for new Pd-only washcoat formulations.

In joint partnership with its catalyst suppliers, Ford has made significant advances in the performance of Pd-only three way catalyst (TWC) technology through improvements in catalyst oxygen storage. The following manuscript describes in detail the performance advancement of Ford's Pd-only washcoat technology through the use of laboratory, engine dynamometer, and vehicle emission data.

The effect of MMT on the OBD-II catalyst efficiency monitor has been investigated. The results conclusively show that manganese which is deposited onto the catalyst during the combustion of MMT- containing fuel provides for an increased level of catalyst oxygen storage capacity. This added oxygen storage was found to result in a reduced rear EGO sensor response and caused malfunctioning catalysts to be incorrectly diagnosed by the OBD-II catalyst efficiency monitor.

Measurements of oxygen storage capacity (OSC) and HC conversion efficiency for 17 catalysts were carried out in the laboratory. All catalysts with steady state HC efficiency below 90% were found to have roughly equivalent and very low capacities to store oxygen. However, catalyst oxygen storage capacity was seen to rise sharply with HC conversion efficiency in excess of 90 percent. These results parallel the trends which are observed between rear HEGO/EGO indexes for OBD-II catalyst monitoring and HC conversion efficiency. In addition, temperature programed reduction (TPR) was found to lend insight into the relationship between catalyst OSC and HC conversion efficiency by providing a qualitative understanding of the mechanisms by which OSC deteriorates. TPR profiles showed that most of the usable oxygen storage is derived from surface ceria which is interacted with precious metals.