A study of the soot burning efficiency of an SCRF® catalyst vs a CSF during active regeneration events

Lasitha  Cumaranatunge, Johnson Matthey Inc.

Modern diesel engine after-treatment systems contain a precious metal Catalyzed Soot Filter (CSF) to reduce particulate atter (PM) emitted from the engine. This is typically followed by a Selective Catalytic Reduction (SCR) catalyst that mitigates the NOx emissions from the engine. SCRF® technology combines the PM and NOx reduction functions into a single component, which not only enables the reduction of the packaging envelope of after-treatment systems, but also allows for higher NOx conversions due to the warmer temperatures in the SCRF® catalyst compared to an SCR catalyst located downstream of the filter component.

The soot management in the filter component is done either via the continuous combustion of soot under normal operating conditions by the NO2-soot reaction (known as passive regeneration) or by triggering a periodic high temperature event with additional fuel injection, also known as active regeneration. It is well known that the NO2 reaction with soot during passive regeneration is significantly higher on a CSF compared to an SCRF® catalyst. In an SCRF® catalyst, there is competition for the NO2 formed over the upstream DOC between the soot combustion reaction and the SCR reaction. In addition to the NO2 formed over the upstream DOC, a CSF also oxidizes NO to NO2 within the filter component due to the PGM coating and hence has more NO2 available for the soot combustion reaction compared to an SCRF® catalyst. However, the NO oxidation reaction is thermodynamically equilibrium limited at the typical active regeneration temperatures (550-650oC). Therefore, the NO2-soot reaction is expected to have less of an impact on the overall soot combustion efficiency compared to the O2-soot reaction that is believed to be the dominating soot combustion reaction under active regeneration conditions.

This study will compare the soot combustion efficiencies of a CSF vs an SCRF® catalyst under active regeneration conditions to determine the factors impacting the soot combustion efficiencies for the two different technologies.

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