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A study of the application of base-metal- and precious-metal-doped base metal direct soot oxidation materials to the remediation of diesel particulate matter has been performed. The study has addressed the impact of reactive gas environment on the de-coupling of catalyst to soot contact, the control of secondary emissions of CO, HC and NOx and the impact of "dilution" of the washcoat by the substrate mass. These studies have confirmed previous findings regarding the toxic effect of NO₂ generation at the catalyst-soot interface but also demonstrate that under ideal circumstances propagation of the exotherm related to CO and (especially) HC light-off can result in an "exotherm cascade" capable of providing soot ignition at T ≺ 250°C.

The reduction of diesel emissions will remain a major challenge in the near future. Based on the expected emissions legislation for Europe and NAFTA, respectively, two main routes to approach this challenge are possible. Especially for the NAFTA market the use of a NOx emission control system is highly probable due to the established low limit for NOx emissions. From today's point of view only two systems - the NOx storage catalyst and the SCR catalyst system - have the potential to reach these limits. In Europe the expected Euro5 NOx limit can most likely be reached by engine measures only. Nevertheless both markets have the common understanding that besides the further improvement by internal engine measures the diesel oxidation catalyst (DOC) as well as the catalysed diesel particulate (DPF) filter will play an essential role in diesel emissions reduction.

This paper will discuss a number of different matters relating to the regeneration of catalyst coated diesel particulate filters such as: impact of the catalyst on the soot ignition temperature, soot combustion rate and NO2 generation. If catalytic coatings prove to be sufficient compared to certain fuel additives they could be used in second generation diesel particulate aftertreatment systems. Examples will be shown on how catalytic diesel particulate filters (“DPF”) can operate on a common rail passenger car diesel engine. Furthermore, an outlook is given on the future combination of particulate - and NOx - emission control for diesel passenger cars.