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A Cu/ZSM-5 catalyst has been tested in both the laboratory and in a gasoline-fueled, lean-burn car. This catalyst is generally believed to be the current “state of the art” for removing NOx from lean engine exhaust. The laboratory tests showed that the HC species was the exhaust component which reduced the NOx. This catalyst actually produced CO, but the CO had no impact on the NOx reduction. The NOx conversion was inhibited by oxygen at oxygen levels below 4%, but was also modestly inhibited by oxygen levels above 4%. The NOx, conversion of these catalysts was less affected by SO2 than were the HC and CO conversions. These catalysts showed very poor thermal durability, losing much of their activity after aging under conditions milder than those typically used for three-way catalysts. The vehicle tests of the fresh Cu/ZSM-5 catalyst showed between 30 and 40% average NOx conversion.

A variety of lightoff and sweep tests were developed to characterize the performance of three-way catalysts using a computer-controlled laboratory reactor. Both fresh and thermally aged pelleted catalysts were characterized using these lightoff and sweep tests. For all of the lightoff and sweep tests, the aged catalyst showed a loss of performance when compared to the fresh catalyst. Although the tests which use a cycled environment show better agreement with engine dynamometer tests, the non-cycled tests were generally better able to distinguish between fresh and thermally aged catalysts. These results imply that while the laboratory reactor can perform tests which closely simulate the dynamic behavior of engine exhaust under closed-loop control, non-cycled tests may be more useful in ranking catalysts for durability.