Comparison of Vehicle Aged SCR Catalyst on a Particulate Filter (SCRF) with Oven Aged Equivalent

Abstract

To meet forthcoming Euro 6 Diesel engines NOx emissions legislation; highly efficient after-treatment systems are required. The use of urea or ammonia SCR is a well-established solution for high NOx abatement for diesel engines. The combination of a Cu-Zeolite SCR catalyst and a diesel particulate filter has been widely investigated in recent years to respond to the European NOx emissions regulations especially for those on light-duty vehicles. The after-treatment systems are preferred to be durable during the entirety of vehicle use. Indeed, the SCRF system must withstand the temperature resulting from the active regeneration of the particulate filter continuously. A 160,000 km vehicle aged SCRF catalyst which has endured more than 91 hours at temperatures superior to 600°C during the regeneration of the particulate filter was compared to an SCRF catalyst aged in the laboratory oven for 16 hours at 800°C with 10% H₂O. The vehicle aged SCR has not only been exposed to the hydrothermal ageing generated by the diesel particulate regeneration but also has seen chemical elements from urea decomposition, soot accumulation, engine oil and fuel residues. In this paper, deeper comprehension of the behaviour the SCRF catalyst during vehicle ageing was exposed. It is evident that the loss of NOx activity is not only due to the regeneration of the particulate filter but also to the possible contamination from the urea injection and the elements present in the diesel fuel and engine oil. XRF results demonstrate that the concentrations of poisoning elements coming from the engine oil or fuel are concentrated mainly at the outlet of vehicle aged SCRF catalyst. Also, results reveal that the poisoning elements have affected the SCR activity of the vehicle aged SCRF catalyst. Finally, it was possible to establish a correlation between a 160,000 km vehicle aged SCRF catalyst and an equivalent SCRF aged for 16 hours at 800°C.