NOx and PM Reduction from Diesel Exhaust Using Vanadia SCRF
Future heavy-duty diesel (HDD) engines are designed to have higher engine out NOx, for improved fuel economy, while reduction of the emission control technology footprint is also desired. Consequently, higher NOx reduction across compact emission control systems is required. Selective catalytic reduction (SCR) catalyst coating combined with a wall flow particulate filter (SCRF®1) is a technology that enables abatement of NOx emissions in addition to oxidation of soot from diesel engine exhausts. Vanadia based-SCR is well known for NOx reduction and is active for hydrocarbon (HC) and particulate matter (PM) oxidation. This dual functionality (oxidation and reduction reactions) of the V.SCR catalysts plus the filtration achieved by the filter substrate can help certain diesel engine applications achieve the legislative limits with a reduced packaging volume.
In this work, the NOx reduction and PM oxidation over filters coated with V.SCR coating (V.SCR-DPF) were studied independently and simultaneously. The effect of various parameters such as washcoat loading, filter type, ANR, and NO2/NOx were investigated on engine. The V.SCR-DPF catalyst was tested with a diesel oxidation catalyst (DOC) upstream. The results confirm that significant NOx and PM reduction can be obtained over transient cycles and at steady state conditions. In general, more than 70% NOx conversion was obtained over a degreened V.SCR-DPF on hot NRTC (Average Temperature = 300°C) and more than 90% NOx conversion when it is coupled with a V.SCR catalyst and ammonia slip catalyst (ASC). After aging at 550°C for 50 hours, a slight improvement in NO conversion was obtained over the SCR-DPF. Passive filter regeneration was investigated starting with both a clean and a soot loaded (3g/L) V.SCR-DPF. Good passive regeneration was obtained for both cases during consecutive NRTC test cycles, where the backpressure stabilized after ca. 20 cycles. In addition, good particle number (PN) filtration was obtained over V.SCR-DPF while meeting expected 2019 EU regulation targets for non-road applications.
Furthermore, computational modeling tools were developed, which are able to predict NOx reduction and passive regeneration for this technology over different engine test conditions. The model was developed by combining kinetics for a V.SCR catalyst, originally developed for a flow through monolith, with a physical model for a coated particulate filter. The reaction kinetics were developed using reactor data. The model has been successfully validated against engine data.