Performance and Durability of Pt- and PtPd-DOC in Diesel Particulate Filter Applications with Active Regeneration 2016-01-0926
The tightening pollutant emission limits require the use of active aftertreatment methods for NOx and particulate matter (PM). Diesel particulate filter (DPF) is a part of commercial aftertreatment system (ATS). PM accumulated in DPF is continuously passively or periodically actively regenerated with the assistance of efficient diesel oxidation catalysts (DOC) having a high efficiency and durability in hydrocarbon (HC), NO and CO oxidation reactions. A high HC concentration during fuel feeding in active regeneration is demanding for DOC. The deactivation in air, hydrothermal, sulfation and active regeneration conditions were evaluated with platinum (Pt-) and platinum-palladium (PtPd)-DOCs by laboratory simulations using the ageing temperature and time as primary variables. The oxidizing conditions with a high oxygen concentration without HCs were deactivating DOCs clearly more than active regeneration conditions with a low oxygen and high HC concentration at 700-800°C. It was found a correlation to between rapid aged laboratory samples and a DOC field-aged for 2000 hours in an actively regenerated DOC+DPF system. These rapid ageing principles with a confirmed correlation can be applied for the development of real applications.
The addition of a small amount of Pd on Pt-DOC (Pt → Pt:Pd = 4:1, 2:1) improved significantly the HC oxidation efficiency of aged DOC in the active regeneration with high HC feed concentration (C1 0.6-1.2%). In normal diesel exhaust with a low HC concentration (500 ppm C1), Pt-only was still slightly better as sulfated. It was concluded that the role of Pd on the PtPd-DOC performance in active regeneration conditions is more the promotion in high HC feed conditions than the thermal stabilization. The oxidation selectivity of various diesel HCs (propene, propane, toluene, decane) was also analyzed on Pt- and PtPd-DOCs. In addition, active regeneration with fuel injection and higher temperatures was able to regenerate the sulfated Pt- and PtPd-DOCs.