A Study of the Soot Combustion Efficiency of an SCRF^® Catalyst vs a CSF During Active Regeneration

The soot combustion efficiency of a Pt-based catalyzed soot filter (CSF) was compared to a Cu-SCR catalyst-coated soot filter (SCRF^® catalyst) under active regeneration conditions. The CSF was found to have a significantly higher soot combustion efficiency compared to the SCRF^® catalyst under typical active regeneration conditions (550–600 °C). Despite the thermodynamic equilibrium limitation of the NO oxidation reaction at high temperatures and the relatively small quantity of NO_x in diesel exhaust compared to O₂, there is sufficient NO₂ production capacity in a CSF where the impact of NO₂ to the overall soot combustion efficiency under active regeneration conditions is significant. The differences between a standard porosity filter typically used for a CSF vs a high-porosity filter used for an SCRF^® catalyst can only account for a minor portion of the difference in the soot combustion efficiency observed between the CSF and SCRF^® catalyst. The fast consumption of the NO₂ produced in situ in the CSF by soot may be driving the thermodynamic equilibrium of the NO oxidation reaction to continuously produce more NO₂ for further soot combustion during active regeneration, resulting in a significant increase in the soot combustion efficiency in a CSF compared to an SCRF^® catalyst or an uncoated filter.