Mechanism Understanding for NOx storage, release and reduction on Pt doped Ceria based Catalysts

The introduction of increasingly more stringent regulations for tailpipe emissions of lean-burn gasoline and diesel engines presents the need for further optimisation of existing aftertreatment technologies. These legislations focus primarily on the reduction of NOx at low temperature, i.e., during the cold start period of engine operation. High surface area ceria is successfully employed as an excellent support of PGMs in commercial catalytic LNT (Lean NOx Trap) systems for automotive emission control. Platinum supported on ceria shows enhanced NOx storage at low temperatures (150-300˚C), together with improved hydrocarbons light-offs. The OSC (Oxygen Storage Capacity) of ceria can be further enhanced using dopants. Their main function is to allow the catalyst to function outside of the normal working temperature range and widen the operating conditions to increase catalyst efficiency. To this end, Samarium was selected as the doping element because of its reported effect on Pt reducibility and the Pt-ceria interaction, which allow for higher storage capacity during lean operation as well as enhanced activation during rich purge. Sm doped catalysts (10 wt.%) were synthesised on a range of ceriabased catalysts with increasing loadings of Pt (0-1 wt.%). The objective of this study was to investigate the effect of the dopant on the performance of the different catalysts, and, to correlate their reactivity with the morphological changes observed on the surface.