Durability of Ultra Thin Wall Catalyst Solutions at Similar Restriction and Precious Metal Loading 2000-01-2881
FTP emissions from a 2.2L four cylinder vehicle are measured from six different converters. These converters have been designed to have both similar flow restriction and to have similar platinum group metals. The durability of these six converters is evaluated after dynamometer aging of both 125 and 250 hours of RATsm aging. These catalytic converters use various combinations of 400/3.5 (400 cells/in2/3.5mil wall), 400/4.5, 400/6.5, 600/3.5, 600/4.5, and 900/2.5 ceramic substrates in order to meet a restriction target and to maximize converter geometric surface area. Total catalyst volume of the converters varies from 1.9 to 0.82 liters. Catalyst frontal area varies from 68 cm2 to 88 cm2. Five of the six converters use two catalyst bricks. The front catalyst brick uses either a three-way Pd washcoat technology containing ceria or a non-ceria Pd washcoat technology. To minimize dependence on palladium the rear brick uses a Pt/Rh washcoat at a loading of 0.06 Toz and a ratio of 5/0/1. Pd loadings are 0.1 troy oz. of Pd. Two independent sets of converters are aged for 125 and 250 hours of RATsm-820 prior to the emission evaluations. FTP results show that washcoat technology and catalyst substrate can have a significant impact on the durability of HC and NOx emissions. Larger catalyst volumes are more robust to high temperature aging. Various combinations of ultra-thinwall substrate demonstrate the potential of reducing catalyst volume by 50% at similar converter restriction and PGM loadings. Converters with ceria containing Pd front brick catalysts have better emission performance after 125 hours of aging than the converters that used non-ceria Pd catalysts. However, both of the ceria and non-ceria Pd containing converters have similar performance after 250 hours of severe thermal aging. 900 cpsi substrates with three-way Pd catalyst demonstrated excellent NOx light-off durability and may be recommended as part of a LEV-II emission solution.