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 (NO 2 ) occurred in both combinations. The selective catalytic reduction (SCR) system was also installed for NO and NO 2 abatement, and NO and NO 2 were evaluated based on the conversion efficiency. The fast SCR reaction, which involves both NO and NO 2 , was dominantly activated at the SCR inlet temperature of 380 °C because the NO 2 /NO X 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 (N 2 O), which has 298 times more global warming potential than carbon dioxide, was also investigated mainly over the SCR. N 2 O has increased dozens of times over the SCR, and a lower ratio of N 2 O emission after the SCR to the NO X at the SCR inlet was obtained in the Pt-reduced combination than in the non-reduction combination.