Enhancement of Diesel Soot Combustion with Oxygen on Particulate Filters After Injection of Dicyclopentadienyl Iron (Ferrocene) in the Exhaust Pipe

For the regeneration of diesel particulate filters with oxygen, temperatures above 550°C are normally required. The increase of the exhaust gas temperature to temperatures above 500°C demands a large amount of energy, so that strategies to reduce the regeneration temperature have to be considered. One option is the injection of a catalyst, which reduces the required regeneration temperature. Hence, a system was developed at HJS Emission Technology GmbH to inject catalyst-precursor into the exhaust gas pipe, whereby the catalysts are generated due to decomposition of the precursor in the hot exhaust gas. A technique based on the calculation of apparent activation energies was developed to characterize the soot combustion on the filter. In the first step metal oxide catalysts, like cerium(IV)oxide, manganese-oxide and iron(III)oxide were investigated after injection of their nitrate precursors dissolved in water. These catalysts showed poor activities, by the reason of the low specific surfaces of the catalyst particles, which were achieved from the decomposition of the nitrate precursors. In the next step, ferrocene (dicyclopentadienyl iron) dissolved in toluene was used as a precursor for the generation of the iron(III)oxide catalyst. The advantage of dicyclopentadienyl iron is the fact that it sublimes into the gas phase at temperatures above 90°C. The catalyst is then generated from gaseous ferrocene in the exhaust pipe, whereby catalyst particles far below 1 µm can be achieved. Experiments revealed much higher activities of the iron(III)oxide catalysts generated from dicyclopentadienyl iron compared to the nitrate precursor. Additionally the dependency of the catalyst performance on the catalyst-soot ratio was investigated in detail. An iron(III)oxide-soot ratio of 4 wt% was determined to be a reasonable value for the regeneration of the diesel particulate filter.