NO, NO2 and N2O emissions over a SCR using DOC and DPF systems with Pt reduction

Abstract

A Pt-reduced diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) combination was used to evaluate the influences of Pt reduction on the oxidation performance in a nonroad diesel engine. For the Pt-reduced combination, a mass fraction of 1.5% Pt in the DOC was lower than a DOC of a non-reduction combination. These DOCs were composed of Pt only. The DPF in the Pt-reduced combination was composed of Pt and Pd with a 2:1 ratio, i.e., Pd was substituted for Pt. Whereas the DPF in the non-reduction combination was Pt only. The oxidation performance in the DOC and DPF systems of the Pt-reduced combination was relatively consistent with the non-reduction combination. The behavior of the undesirable oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) occurred in both combinations. The selective catalytic reduction (SCR) system was also installed for NO and NO2 abatement, and NO and NO2 were evaluated based on the conversion efficiency. The fast SCR reaction, which involves both NO and NO2, was dominantly activated at the SCR inlet temperature of 380 °C because the NO2/NOX ratio is approximately 60%. The fast SCR reaction competed with the standard SCR reaction above 380 °C, and then the standard SCR reaction became the prevailing reaction as the temperatures increased. Nitrous oxide (N2O), which has 298 times more global warming potential than carbon dioxide, was also investigated mainly over the SCR. N2O has increased dozens of times over the SCR, and a lower ratio of N2O emission after the SCR to the NOX at the SCR inlet was obtained in the Pt-reduced combination than in the non-reduction combination.