Ocampo, F., Ohtake, N., and Southward, B., "Recent Developments for CeBa Hybrid Materials with Enhanced Properties for BS-6 NOx Storage Applications," SAE Technical Paper 2017-26-0123, 2017, doi:10.4271/2017-26-0123.
In order to achieve NOx tailpipe targets of current diesel regulation standards two main catalytic technologies have been employed, specifically NH3-SCR and LNT. However both of these technologies face challenges with the implementation of newer / colder test cycles such as “Real Driving Emissions” (RDE), combined with CO2 targets (95 g/km is 2020 target in Europe). These cycles will require higher NOx Storage Capacity (NSC) in the low temperature region (120-350°C). Conversely, lean-burn Gasoline vehicles, with their higher operational temperatures, will require improved NSC over a broader temperature range (200-500°C). Therefore, the development of NSC materials to meet these opposing requirements is an area of extensive study by Original Equipment Manufacturers (OEMs), washcoaters, and raw materials suppliers. Today, ceria is a key component in the formulation of active NSC washcoats. It is often combined with barium in order to improve its high temperature NSC, but this also leads to a significant loss of specific surface area and thus a decrease in overall performance at low temperature. This paper reports recent progress made on NSC materials, with the aim to enlarge their operational temperature window. In this regard, Solvay has developed an innovative solution: rare earth and barium hybrid compounds as advanced NSC materials, the details of the development and optimisation being described herein. Synthetic gas bench tests were performed on powder model catalysts and show a significant increase in NSC at low temperatures and a significant benefit in NSC at high temperatures in comparison to a current commercial reference, Solvay ‘High Stability Ceria’ doped with Barium (or ‘Basic Ceria’). A range of hybrid products were developed with different acido-basic properties in order to optimize the trade-off between stability, NOx performance and desulfation capacity depending on the application specific needs.