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In order to simulate the aging of the emission control system over the life of a vehicle, a variety of engine dynamometer cycles has been developed that accelerate the catalyst aging processes. This paper investigates the sensitivity of automotive emission control catalysts to their aging and testing environments. To show the effects of aging conditions on catalytic performance, three engine stand dynamometer aging cycles were utilized. These aged catalysts were then tested on two test vehicles: one featured multi-point fuel injection; the other, sequential electronic fuel injection. The performance results indicate the sensitivity of a catalyst to aging conditions as well as the various parameters of its operating environment. This sensitivity varied for the two catalyst formulations.

As legislation tightens in the Heavy Duty Diesel (HDD) area it is essential to develop systems with high activity and excellent durability for both Particulate Matter (PM) and NOx control. The Continuously Regenerating Trap (CRT™) system controls hydrocarbon (HC), CO and PM emissions from HDD vehicles with efficiencies of over 90%, and has demonstrated very good field durability over distances exceeding 700,000 km. The system is widely used in Europe, and is demonstrating the same high performance and excellent durability within field applications in North America. The Continuously Regenerating Trap (CRT™) system has been developed and patented by Johnson Matthey [1]. Throughout this paper this system will be referred to as the Continuously Regenerating Diesel Particulate Filter, CR-DPF. The CR-DPF comprises an oxidation catalyst, optimised for NO2 generation from the engine-out NOx, and a downstream DPF.

The effective use of a catalyst to initiate regeneration of a diesel particulate trap has traditionally been based on the concept that the catalyst coated onto the trap adsorbs particulate, and activates oxygen in the exhaust causing initiation of particulate combustion. Reported regeneration temperatures generally lie in the range of 350°C and above. This paper reports on a new mechanism of diesel particulate combustion involving activation of oxygen over a catalyst to form NO2, which is then capable of adsorbing on diesel particulate trapped in a filter and initiating combustion at lower temperatures. Diesel particulate has been combusted on a wire mesh trap at temperatures as low as 265°C, and this regeneration capability has been maintained over hundreds of hours of operation. However, the most active catalysts for low temperature activation of diesel particulate are also high sulfate producers.

The primary topic of this paper is the evolution of the early oxidation catalysts of the 1960's to present-day sophisticated three-way catalysts. Early catalyst formulations are described, along with the chemistry of catalytic emission control for automobiles. The evolution in catalyst formulations and engine control strategy is discussed at length. Precious metal supply and world emission regulations are discussed briefly. The scope of this paper is primarily limited to the U.S. automotive industry and the U.S. standards.