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Lean NOx traps (LNT) are currently the technology of choice for treating the NOx emissions from lean burn gasoline engines. With the help of the newly established low sulfur fuel to be introduced in the European and the U.S. markets, the widespread application of LNT technology becomes more promising. However, we found that the sulfur tolerance of aged LNTs is much lower than that of the fresh LNTs. Moreover, the aged LNTs are more difficult to be desulfated relative to the fresh ones. The robustness of the LNT still needs to be improved. This work is focused on understanding the fundamental processes of sulfur poisoning and desulfation as the trap ages. Three LNT samples were selected from different suppliers. These samples were subject to different aging conditions. Flow reactor and pulse flame combustor tests were conducted on the samples to evaluate their performances with regard to sulfur poisoning and desulfation.

Concern in Europe about the environmental impact of the car has lead to ever more stringent emission legislation, and in the near future, conformance to this emission legislation to extended mileage, typically 50,000 miles, will be required. Vehicle manufacturers prove out this conformance by emission testing vehicles at this extended mileage. Mileage accumulation takes several months, so there is a clear need to develop a process which replicates this vehicle aging in a much reduced time frame and cost. This paper describes an engine dynamometer based catalyst aging process and the correlation to European ‘worst case’ 50,000 miles vehicle aged catalysts. Correlations have been achieved for close-coupled catalysts taken from a 1.3 8V and 1.25 16V B-Car sized vehicle. The significance of this correlation allows representative vehicle aged catalysts to be delivered in hours as opposed to months.

The effect of changing catalyst precious metal ratios and loadings on close coupled catalytic converter efficiencies has been studied. The three precious metals were platinum, palladium and rhodium. The specific matrix used for the development of response surface models is a central composite design and provides the capability of visually optimising the precious metal loadings. Catalysts were evaluated using perturbed scans. lightoff curves from the dynamometer aged, and vehicle emission tests. These scans show percent conversion efficiencies of the three legislated gases; HC, CO and NOx, over a range of Air Fuel Ratios (λ). Whilst lean and rich lightoff curves provide indications of conversion efficiencies at varying temperatures. Prior to testing the catalysts were aged, using an accelerated dynamometer ageing process, to 80K simulated kilometres. The catalysts were then fitted to a vehicle and chassis roll emission tests conducted.