Axial characterization of lightoff and underfloor catalytic converters vehicle-aged on a 5.8 L Corvette

Catalysts taken from the lightoff and underfloor converters of two 1986 Corvette exhaust systems which had been vehicle-aged for 100,000+ miles were cut into 1 inch thick sections along their axis and characterized for lean lightoff and warmed-up performance using a laboratory reactor. Sections were then treated to remove the poisons, and the characterization was repeated. An axial gradient in both lightoff and warmed-up conversion efficiency for HC and CO was, detected within the first 2 inches of both lightoff converters for both vehicles. This activity gradient is in agreement with the gradient in the phosphorus and zinc concentrations found in the front 2--3 inch sections of the lightoff converters. Comparison of these data sets with those obtained after removal of the P and Zn poisons led the authors to conclude that a significant part of the total deterioration of activity can be attributed to phosphorus and zinc poisoning for the front 1 inch (and to a lesser extent for the second 1 inch section) of the lightoff converters.