Performance Studies and Correlation between Vehicle- and Rapid- Aged Commercial Lean NO_x Trap Catalysts

摘要

Even though substantial improvements have been made for the lean NO_x trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NO_x storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, and one reason for this could be limited NO oxidation. In addition, the oven-aged sample was found to be well correlated to the vehicle-aged catalyst. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance under real driving conditions and monitor the gradual deterioration of the vehicle-aged catalyst during the vehicle aging testing.