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Alumina-supported manganese catalysts with cryptomelane and/or birnessite structure have been prepared using a simple method based on the thermal decomposition of potassium permanganate. The samples have been characterized by XRD, FTIR, TGA, DSC, N 2 adsorption at −196 °C, SEM, H 2 -TPR and XPS, and their catalytic activity for soot combustion has been tested and compared to that of a reference Pt/alumina catalyst. The thermal decomposition of alumina-supported KMnO 4 yields a mixture of supported birnessite and potassium manganate which is the most effective, among those prepared, to lower the soot combustion temperature. However, this material is not useful for soot combustion because the accelerating effect is not based on a catalytic process but on the oxidation of soot by potassium manganate. A suitable soot combustion catalyst is obtained after potassium manganate is removed by water washing, yielding only the birnessite phase OPEN ACCESSCatalysts 2012, 2 353 on the γ-Al 2 O 3 support. This birnessite phase can be transformed into cryptomelane by calcination at 600 °C. These two samples, γ-Al 2 O 3 -supported birnessite and cryptomelane are suitable catalysts for soot combustion in NO x /O 2 mixtures, as their catalytic activity is based on the NO 2 -assited mechanism, that is, both catalysts accelerate the oxidation of NO to NO 2 and NO 2 promotes soot oxidation. The soot combustion temperatures obtained with these birnessite/cryptomelane alumina-supported catalysts are similar to that obtained with the reference Pt/alumina catalyst.

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