Honda diesel engine vehicles that go on the market in 2018 will be equipped with a newly developed silver (Ag)-type catalyzed diesel particulate filter (cDPF). Ag has high particulate matter (PM) oxidation performance, but conventional catalyst-carrying methods cause weak contact property between PM and Ag; therefore, the newly Ag-type cDPF was developed on the concept of enhancing the property of contact between PM and the catalyst to realize contact property enhancement at the macro, meso, and nano scales. As a result, the newly developed catalyst showed an enhancement of T90 performance by a factor of approximately 2 relative to the conventional Ag-type catalyst in fresh condition.
Durability in the environment of an automobile in use was examined through hydrothermal aging, lean-rich (L/R) aging, sulfur (S) poisoning, and ash deposition. The results have confirmed that hydrothermal aging is the greatest factor in deterioration. The reason is that Ag sintering diminishes the PM-catalyst contact property. Therefore, in order to enhance hydrothermal durability, an examination was made on additives that would inhibit Ag sintering. It was found that adding neodymium (Nd) had the effect of enhancing Ag dispersion and inhibiting sintering, yielding an enhancement of approximately 10% in PM oxidation performance after hydrothermal aging.
Hydrogen sulfide (H2S) removal performance, which is a feature of the Ag catalyst, is also maintained at a level equal to or better than the cDPF deployed in 2015. The 2018 after-treatment system is compact and does not require placement of a separate catalyst for H2S removal. In addition, peak oxidation temperature that is unusual temperature rise can be limited by controlling the catalyst coating along the axial direction.
The enhancement of the developed catalyst was also confirmed by its durability in actual operation. It reduced the regeneration time 32% shorter than the cDPF deployed in 2015.
This Ag-type PM oxidation catalyst is expected to ameliorate four issues faced with diesel particulate filter (DPF) regeneration: (1) deterioration in fuel consumption, (2) increase in carbon monoxide (CO) and hydrocarbon (HC) emissions, (3) thermal deterioration in upstream oxidation catalyst, and (4) oil dilution.
