Deactivation of Soot Combustion Catalysts by Perovskite Structure Formation

Deactivation of Soot Combustion Catalysts by Perovskite Structure Formation 

The formation of perovskite structures does not always have a positive effect on the soot combustion activity of mixed oxides, and a few examples of catalyst deactivation due to perovskite structure formation have been reported. The stability of Ba, I /Ce02 catalysts, which have been shown to be very active in soot combustion, was studied. This catalyst was thermally stable after 30 h at 800 °C, but above 830 °C catalyst deactivation due to BaCe03 perovskite structure formation was observed [46]. Ba/Mn-Ce catalysts were also tested for soot oxidation in the presence of NO,c concluding that the formation of perovskite-type oxides after the high-temperature calcination caused the loss of NO storage capacity and a small increase in soot oxidation temperature, but did not seem to affect the NO oxidation activity [47]. 

The literature available related to the utilization of perovskites as soot combustion catalysts has been reviewed in this chapter, and some general conclusions can be summarized. 

The general formula of perovskites is ABO3, and soot combustion perovskite catalysts with many different cations have been reported for both A and B positions. The most studied formulations include transition metals that are able to accomplish redox cycles, such as Mn, Ni, Cu, Co, and Fe among others. The partial substitution of one of the cations usually has a positive effect on the perovskite activity, and alkali metals seem to be the most studied dopants. 

However, the excess of dopant or an inappropriate synthesis method can lead to the segregation of phases and this could decrease the activity. 

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