Durability of an UF HC Trap/SCR Catalyst System Applied to a 4-Cylinder PZEV Calibrated Vehicle 2018-01-0336
A 1.0 L underfloor converter of a 1.4 L PZEV calibrated vehicle was replaced with a 1.26 L HC trap and a 1.26 L SCR catalyst. The HC trap consisted of a zeolitic storage layer beneath a three-way catalyst layer. A newly developed catalyzed HC trap technology containing Pd/Rh was used in the current study. Increased trapping efficiency and conversion was assigned to rapid and efficient polymerization of small alkenes and aromatics coupled with more efficient combustion before release. The new trap features include the presence of strong Brønsted acidity, precious metals such as Pd and a base Mn+ redox active metal. The HC trap was followed by an SCR catalyst for NOx clean-up. The production close-coupled catalyst and replacement underfloor catalysts (HC trap and SCR) were aged on a combination of rural and highway roads for 150,000 miles. Peak bed temperatures during road aging of the HC Trap and SCR catalyst were approximately 600 °C. Vehicle FTP and US-06 tests were conducted at 9 intervals between 2,000 and 150,000 miles. In general, the FTP emissions did not change significantly with mileage. At 150,000 miles, FTP nMHC and NOx emissions were 6 and 22 mg’s/mile, respectively. At 150,000 miles, the HC Trap reduced HC and NOx emissions by 6 and 19 mg/mile, respectively. US-06 nMHC + NOx emissions were consistently below 10 mg/mile. Due to the effectiveness of the HC trap on this application, the SCR had no significant impact on HC emissions, and a small benefit for NOx.