Post Mortem of an Aged Tier 2 Light-Duty Diesel Truck Aftertreatment System

A 2005 prototype diesel aftertreatment system consisting of diesel oxidation catalysts (DOC), Cu/zeolite Selective Catalytic Reduction (SCR) catalyst, and Catalyzed Diesel Particulate Filter (CDPF) was aged to an equivalent of 120k mi on an engine dynamometer using an aging cycle that incorporated both city and highway driving modes. The program demonstrated durable reduction in particulate matter (PM) and nitrogen oxides (NOx) emissions to federal Tier 2 levels on a 6000 lbs light-duty truck application. Very low sulfur diesel fuel (∼15 ppm) enabled lower PM emissions, reduced the fuel penalty associated with the emission control system, and improved long-term system durability. A total of 643 filter regenerations occurred during the aging that raised the entire catalyst system to high temperatures on a regular basis. After testing the aged system on a 6000 lbs light-duty diesel truck, a post mortem analysis was completed on core samples taken from the DOC, SCR catalyst, and filter. It was found that the outlet of the DOC and the inlet of the SCR were deteriorated most significantly. Known catalyst poisons such as P were found in the DOC and SCR washcoats. The filter contained residual ash that was composed mainly of Ca, P and Zn compounds. The inlet of the SCR catalyst contained Pt that degraded the NOx conversion in that portion of the catalyst. Overall, the system was still quite functional and delivered 74% NOx conversion on the U.S. Federal Test Procedure (FTP-75) for light-duty vehicles