Impact of sulfur on the performance of vehicle-aged palladium monoliths

Abstract A commercially prepared catalyst which uses Pd technology and which had been vehicle-aged for 56 000 miles was characterized for three-way catalytic performance in a laboratory reactor under conditions simulating the operation of the catalyst in a vehicle. The tests were conducted with the concentration of SO 2 in the simulated exhaust feedstream set at 1 ppm, 5 ppm and 30 ppm (corresponding to 15, 75 and 450 ppm in fuel, respectively) to evaluate the magnitude and reversibility of the effect of sulfur on HC, CO and NO x activity. Tests were conducted using a propene/propane mixture as a surrogate for the hydrocarbon mixture in exhaust. The lightoff and warmed-up activities, particularly for HC and NO x , were found to be deteriorated when SO 2 was added to the simulated exhaust feedstream, in agreement with previous work on the impact of sulfur on three-way catalysts conducted in this laboratory. In addition, the impact on lightoff and warmed-up activity of NO x and HC was found to be generally non-linear with sulfur concentration. The impact of sulfur on activity was found to be partially non-reversible at temperatures below 650°C, but the original activity could be restored when the catalyst was operated at temperatures above 650°C. Consistent with this result, the impact of sulfur on activity was found to be minimal for operation above 700°C.