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Given the substantial differences in geometrical properties between foams and honeycombs a direct comparison with equal coating thickness, amount and precious metal amount is not feasible. We present however systematic comparisons with known precious metal amounts while pointing out important differences in the wash coating characteristics. ...We present however systematic comparisons with known precious metal amounts while pointing out important differences in the wash coating characteristics. As strongly affected, crucial operational characteristics we comment on, are the pressure drop and the homogenizing properties of the substrates on the temperature distribution. ...The comparison of two differently coated foam DOCs have given insights in the conversion dependencies on the coating parameters and have shown further optimization directions.

Most commonly, ash is mixed with fibers deriving from the gasket on the DPF inlet surface, fibers from the intumescing mat around the DPF and the diesel oxidation catalyst (DOC) upstream the DPF, as well as with newly formed V-O long-prismatic nanocrystals originating from the catalytic coating layer. SEM images reveal the presence of a 130-170 μm thick soot cake on the filter walls of RME20- and RME0-DPF. ...EDX analyses of the layer deposited on the channel walls underneath the soot reveal the following elements: Ca, P, Zn, Mg, S, Na (typical ash elements), V, Ti, W (deriving from the catalytic coating) and Fe, Cu from engine wear. The size distribution of individual soot particles in the soot aggregates (average diameter: 21 nm), together with the nanostructure of soot particles obtained by high resolution transmission electron microscopy (HRTEM) indicate that the RME100 soot is relatively more reactive compared to diesel soot.

Other sources are the metallic additives to the lube oil, metallic additives in the fuel, and debris from the catalytic coatings in the exhaust-gas emission control devices. The formation process results in extremely fine particles, typically smaller than 50 nm.