Optimized microwave susceptible catalytic diesel soot trap

The wall-flow diesel particulate filter (DPF) is currently the usual post-treatment system in diesel engines for soot particle abatement in passenger, heavy-duty and non-road vehicles. It consists in alternately plugged parallel square channels, in order to force the exhaust gases to flow through the porous inner walls: soot is so collected on the surface and in the porosity of the channel walls, progressively blocking the pores, making mandatory the filter regeneration. In this work we realised a specific pre-treatment procedure in order to modify the porosimetric characteristics of the bare support, with the aim of increasing the active species load and simultaneously keeping the pressure drop and the filtration efficiency of the final catalytic system in the same range of an uncatalysed DPF. The pre-treatment is based on a controlled chemical erosion of the SiC porous structure with a HF:HNO3 acid solution. The results showed that, if compared with the analogues prepared without acid treatment, the pre-treated samples resulted with a modified pores distribution, with an increased average pore diameter. This important result allowed us to obtain new catalytic filters with higher catalyst load, higher regeneration activity and simultaneously keeping the pressure drop at similar values of the uncatalysed filters. As a consequence of these improved performances, a decrease in the frequency and duration of the regeneration step will be possible without affecting the filtration efficiency, as verified from the deposition and on-line microwave assisted regeneration tests. In particular, the results showed that the simultaneous porosity modification and the higher catalyst loading (30%wt of copper ferrite) allowed to decrease the threshold catalyst temperature to about 350 °C, but more importantly allowed to decrease the regeneration step duration from about 22 to about 15 min. Moreover, the addition of K to the catalyst formulation had the important effect of further decreasing the regeneration time to about 8 min, even if it had no effect on the threshold temperature. So, very positive effects on the performances of the final catalysed filter prepared on the carrier with a modified porosity with the proposed procedure are observed on the energy needed to regenerate the filter: the comparison of the microwave energy supplied, considering the same filter volume (about 0.35 liters), during the microwave assisted regeneration phase of all the filter typologies considered in this work, compared to the traditional fuel post-injection, showed that just the addition of the catalyst allows an energy saving of about 60%, that increased up to 75% after the K addition to copper ferrite to a filter with modified porosity.