Formulations Based on Metal-Doped Ceria

The synergetic interaction between ceria and other metals, when solid solutions are not formed, can also result in very active and resistant catalysts. Several catalyst formulations containing supported transition 

CeriorBased Formulations for Catalysis for Diesel Soot Combustion 591 

Sample Aging temperature ( C) Soot/catalyst ratio (type of contact) O2 (%) 7 (°C) Reference 

A detailed elaboration of the previous mechanism was later suggested by the same group,who proposed a mechanism for soot oxidation that includes the reduction and oxidation of ceria and the formation of potassium carbonate, which decomposes to COg. A key step in the proposed mechanism was the formation of peroxide or superoxide species on the surface of the ceria, which react with soot promoting the transformation of KNO3 to KgCOg and nitrites. 

This mechanism, which does not rely on the redox of ceria, is in agreement with the fact that the action of alkali metals seems to be independent of the type of support. Milt et al found for example that potassium promotes the activity of LagOg thus decreasing the temperature of soot oxidation to the range 350-400 and attributed the increase of activity to the dynamic of formation and the decomposition of carbonate-type intermediates. 

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