On the soot combustion mechanism using 3DOM ceria catalysts.

CeO 2 catalysts have been prepared with conventional (Ref) and three dimensionally order macroporous (3DOM) structures, and the effect of the structure on the soot combustion mechanism has been studied in detail. Isotopic exchange experiments showed that the CeO 2 -3DOM catalyst produces more active oxygen upon O 2 chemisorption than the counterpart CeO 2 -Ref catalyst, and this active oxygen is transferred more efficiently to soot due to the macroporous structure. CeO 2 -3DOM and CeO 2 -Ref also accelerate the oxidation of NO to NO 2 , and their activity is equal. However, CeO 2 -3DOM utilizes NO 2 more efficiently than CeO 2 -Ref for soot combustion. NO 2 has two roles in the soot combustion mechanism: i) reacts with soot and ii) is chemisorbed on ceria and produces active oxygen, which is more oxidizing than NO 2 . In ceria catalysts with a conventional structure, the main role of NO 2 is the direct oxidation of soot, because active oxygen has restrictions to be transferred from catalyst to soot due to the poor soot-catalyst solid-solid contact. However, the 3DOM structure improves the transfer of active oxygen, and therefore, an additional benefit is obtained from NO 2 , that is, NO 2 contributes to active oxygen production and the 3DOM structure allows its efficient transference to soot. [ABSTRACT FROM AUTHOR]