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A method for improving three-way catalyst (TWC) performance by superimposing a low frequency lean air-to-fuel ratio (AFR)bias perturbation onto the standard AFR oscillations is described. This observation of Catalyst Regeneration (CatRegen) has been attributed to a reactivation of poisoned precious metal sites on the catalyst surface. Preliminary tests under steady-state conditions show that there is a gradual reduction in TWC activity for NOx after a lean-rich transition, suggesting a temporary poisoning of the active precious metal sites on the TWC under rich conditions. This deactivation can be prevented by periodically exposing the catalyst to lean exhaust gas; which has led to the development of the CatRegen system.

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.