A Study of Active and Passive Regeneration Using Laboratory Generated Soot on a Variety of SiC Diesel Particulate Filter Formulations 2010-01-0533

In this study an attempt to understand and demonstrate the effects of various washcoat technologies under active and passive regeneration conditions was performed. Six different formulations, on 1.0" D. x 3.0" L. SiC wall flow filters at the laboratory level were used at various test conditions, including variable NO₂/NO

ratios and O₂ concentrations. Samples were regenerated using active and passive conditions to evaluate regeneration rates and the potential impact of regeneration at the vehicle level. Results were applied to vehicle operating conditions to determine passive functionality and potential benefits. Active regenerations at 2% O₂ and 5% O₂ showed no significant difference in time to complete regeneration and soot burn rates. Active regenerations performed at 1% O₂ and 5% O₂ concentration showed that the regeneration temperature was shifted by approximately 50°C. Active soot burn rates were mainly governed by the higher inlet temperature and showed minor differences between Pt-containing washcoats and non-Pt-containing samples. Pt-containing samples provided a much cleaner reaction in that even a low loading of Pt converted ≻ 99% of the soot to CO₂. The Pd-only washcoat also was able to achieve mostly CO₂ as a product. For both non-PGM-containing washcoats and blank substrate there was a 60:40 ratio of CO:CO₂. Overall, a Cu/zeolite-containing sample showed similar results to the blank substrate, in that the regeneration capability was approximately equal to a blank substrate. The significant difference was observed when comparing the soot burn rates from the low- and high-soot-loaded samples. As the soot loading was nearly doubled for each sample the soot burn rate increased by nearly the same value under active conditions only. Comparing the passive regeneration rates for the different cases, the 0.5 blend of NO₂/NO

was on average 2.5 faster then what was observed for the standard or lower NO₂/NO

ratio of 0.15. Results show that if operating in an appropriate temperature range with an inadequate amount of NO₂, the Pt-containing DPF can produce NO₂ from NO and improve the burn rate of the soot to a small degree. Increasing O₂ concentration in exhaust stream and holding the NO only concentration at the inlet led to an increase in NO₂ production for Pt-containing samples. The formation of HNCO was observed over soot-loaded filters containing no washcoat. The HNCO formation resulted from the reaction of gas phase NH₃ and CO generated from the partial oxidation of soot. The presence of NO₂ assisted in increasing the formation HNCO at lower temperatures. One must account for CO, CO₂, and HNCO when calculating the regeneration rate of soot-loaded filters containing no catalyst washcoat.