Catalytic Filter Systems with Direct and Indirect Soot Oxidation Activity

Importance of the oxygen bond strength for catalytic activity in soot oxidation

“…TEM studies by Gardini et al [15] on Ag/soot mixtures have indicated that tight contact corresponds to an extensive interface between primary particles of catalyst and soot, whereas loose contact corresponds to fewer contact points at the interface between coagulates of catalyst particles and coagulates of soot particles. In several experiments [11,[16][17][18][19][20] with oxidation of soot particles filtered from gas streams by a catalytic filter part of the soot oxidation has been observed to peak at a relatively low temperature in the range characteristic of tight contact with the catalyst, while another part of the soot oxidation has been observed to peak at a higher temperature more characteristic of loose contact with the catalyst. Hence an understanding of both tight and loose contact oxidation may be relevant for real filter applications.…”

Visualizing the mobility of silver during catalytic soot oxidation

“…In tests where soot and catalyst are crushed together (so-called tight contact), the oxidation occurs at a significantly lower temperature, compared to when soot and catalyst are stirred together with a spatula (so-called loose contact) [11]. Several experiments with diesel soot filters [10,[12][13][14][15] have indicated the presence of both contact types. An explanation of this may come from the environmental scanning electron microscopy experiments by Kameya and Lee [16], who observed that the catalytic oxidation at the interface between the bottom of the soot cake and the catalyst containing filter caused the soot cake to crack, leading to a delamination and subsequent diminishment or even loss of soot/catalyst contact [16].…”

Update on the Science and Technology of Diesel Particulate Filters

“…The double peak is therefore a direct manifestation of the importance that catalyst layer geometry plays in establishing different modes of contact between the deposited soot particles and the catalytic coating. It is not possible to explain this double peak structure of the soot oxidation curves with a model based only on chemistry, since uncatalyzed soot oxidation exhibits a single peak and the same is true for mixtures of soot-catalyst powders 67) . An example of application of the two-layer model to analyze the soot conversion on a catalytic filter is shown in Fig.…”

“…The problem of soot-catalyst contact in diesel emission control systems was recognized in the 1980s 63) as a barrier for active catalytic filter development, and it has become popularized in more recent laboratory studies of powdered carbon blackcatalyst mixtures, with the introduction of so-called "loose" and "tight" contact 64,65) samples. Direct demonstration of soot-catalyst contact effects on diesel soot oxidation in filters has been published in 67) . A mathematical description of the incomplete sootcatalyst contact, the so-called "Two-Layer Model" was introduced a decade ago, and it has been since incorporated into state-of-the-art DPF simulators 68,69,70,71) .…”

“…The effect of Pe on the soot deposit microstructure, soot-catalyst contact and reactivity is addressed in 72) . CDPF development has to address two key areas 67) :…”