The integration of DeNOx functionality into wall flow filters for the after treatment of diesel engine exhaust gases is a field of technology to which many publications in the recent years have drawn their attention. To integrate the needed amount of catalyst, high porous substrate materials have been developed. A drawback of the high porosity levels of 60% and higher is a significant reduction in mechanical strength. The aim of this work is to provide a new solution based on a high porous SiC material which is treated by a dual layer coating. The first layer is a nanoparticle coating which enhances the mechanical strength of the substrate. It can also be used to improve the catalytic performance and to finally decrease the loading of the second coating layer which is the active catalyst for selective catalytic reduction (SCR) of NOx with ammonia.
Three different types of catalysts have been investigated as the second layer: a Fe-β-zeolite, a mixed metal oxide based on ceria and zirconia and a composition based on titania and vanadia. The impact on the pore structure and the resulting back pressure was investigated as well as the SCR functionality. The results demonstrate that the combination of the initial nanoparticle layer with the different catalyst layers has led to high SCR efficiencies at low catalyst loadings.
Engine bench tests on filters in the size of 5.66″×8″ have been performed to verify the high particle number (PN) filtration efficiency which is required for Euro 6/VI applications and the NOx reduction efficiency by using a diesel oxidation catalyst (DOC) for adjusting the NO2/NOx ratio. The results demonstrate that a new type of a diesel particle filter (DPF) has been developed, in which various types of SCR catalysts can be integrated. This new filter with integrated SCR functionality can be used in the design of exhaust systems with reduced volume, weight and costs, which still meet the Euro 6/VI requirements in respect to NOx and PN reduction for petrol and diesel engines.
