Soot oxidation catalysts

Several researchers have focused their attention on the application of oxide materials to lower the oxidation temperature of soot particulates. It was reported that active soot oxidation catalysts are PbO, C03O4, V2O5, M0O3, CuO, and perovskite type oxides[3]. 

An exploratory study was carried out with respect to the performance of molten salts as diesel soot oxidation catalyst. The activity of two binary eutectic salts, with a low melting point, was measured and compared with the activity of two very active solid single oxides. Also the influence of NO on the oxidation rate was investigated. 

A number of metal oxides was screened upon catalytic activity for soot oxidation by means of TGA/DSC. Several metal oxides appeared to be active soot oxidation catalysts. Contact between catalyst and soot was found to play a major role in this solid-solid-gas reaction varying this contact, activities for several catalysts ranged from active to hardly any activity. It is fUrther tentatively suggested that contact of soot, deposited on catalytic coated particulate filters, is poor, which has major implications for the development of soot oxidation catalysts under diesel operation conditions. 

Tlie objective of tliis study is to investigate tlie influence of above mentioned intrinsic parameters of catalyst and soot on tlie catalytic combustion of soot. In order to be able to study these parameters, first the activity of different soot oxidation catalysts has to be defined properly. The screening of catalyst materials, as presented in this paper, aims to fulfil tliis need. 

DPFs to increase the oxidation rate, prevent uncontrollable soot combustion, and decrease instrumental and energetic loads for the regeneration process. There have been excellent reviews concerning research on catalytic soot oxidation since 1980, when R D of DPFs started. Therefore, after a brief explanation of the commonly used methods for soot oxidation catalyst evaluation, we will classify the recently investigated catalysts into several types, mostly those introduced since 2000, and give detailed explanations of their reaction mechanisms, materials, and situations for practical application. 

Figure 2.3. Experimental configuration of the temperature-programmed reaction (TPR) used to evaluate soot oxidation catalysts.

Numerous soot oxidation catalysts have been reported since the 1980s, because soot oxidation is fundamentally a simple complete oxidation reaction (carbonaceous compounds CO2 + H2O), so that sophisticated catalysts with high selectivity are not required. However, there is a critical problem in establishing contact and interaction, directly or indirectly, between the reactant (soot) and the catalyst, both of which are solid materials. Therefore, soot oxidation catalysts reported to date can be classified according to the assumed working mechanism that solves this problem. In this review the authors classify the catalysts into the four types shown in Fig. 2.5, based on the mediator for the oxidation reaction that connects the active sites of catalyst and soot surfaces mobile catalysts, mobile oxygen catalysts, NO2 mediating... 

Practical Application and Improvement of Soot Oxidation Catalysts... 

Several examples of practical applications and improvement of soot oxidation catalysts, based on the mechanisms discussed, will be explained in this section. 

Furthermore, as clearly demonstrated by the three-way catalytic system for gasoline vehicles and DPNR explained in this chapter, the automobile exhaust gas treatment catalysts do not function alone, but rather require a highly controlled engine system. It is therefore necessary to further develop technologies to functionally integrate engine and after-treatment devices in which the soot oxidation catalyst is a component. 

Tikhomirov, K., Krocher, O. and Wokaun, A. (2006). Influence of Potassium Doping on the Activity and the Sulfur Poisoning Resistance of Soot Oxidation Catalysts, Catal. Lett, 109,... 

Example 9.2-3 A combinatorial approach for the discovery of low-temperature soot oxidation catalysts (Olong et al, 2007). 

Olong, N.E., Stoewe, K. and Maier, W.F. (2007). A combinatorial approach for the discovery of low-temperatue soot oxidation catalysts. Appl. Catal. B Environmental 74,1-2,19-25. 

---