Samarium doped Ceria as an active catalyst for emission control

The introduction of the Euro 7 standards for tailpipe emissions of light-duty vehicles (cars and vans) presents the need for further optimisation of the existing after-treatment technologies. New rules propose a 35% reduction for NOx emissions from these vehicle types compared to Euro 6 standards. Lean NOx Trap (LNT) catalysts are a commonly used for NOx emission control in lean-burn engines, however, their function during cold-start engine operation is a target area for improvement. They consist of PGM(s) supported on ceria or other mixed oxides. Ceria’s redox property allows it to store NOx at low temperatures (<300˚C), independently from exhaust gas conditions. The NOx storage and reduction properties of ceria can be further enhanced using dopants. Rare earth (RE) elements such as Samarium are commonly used in these systems to their reported increase in oxygen vacancies and defect densities as well an altered Pt reducibility and Pt-ceria interaction. These in turn allow for higher NOx storage capacity during lean operation as well as enhanced activation during rich purge. Sm doped catalysts (10 wt.%) were synthesised on a range of ceria and alumina-based catalysts with increasing loadings of Pt (0-1 wt.%). The objective of this study was to investigate the effect that doping had on the catalyst structure and how this in turn affected the performance of the catalyst in realistic conditions. Morphological changes were observed, using many characterisation techniques (H2-TPR, XPS, EELS & Raman Spectroscopy), and oxidation and storage activities were measured in cold-start conditions (150-300˚C).