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Two series of (0-4 wt%) potassium doped oxide catalysts based on iron and manganese spinel were prepared. The synthesized materials were characterized in terms of their structure (XRD, Raman spectroscopy) and surface electronic properties (work function measurements). The catalytic activity towards soot combustion was determined by temperature programmed oxidation of a physical mixture of soot and catalyst in tight contact in gas oxygen mixtures with and without NO addition. For iron spinel based materials, where potassium is localized at the surface, the catalytic activity correlates with the work function lowering upon K doping, while for manganese spinel based materials, where potassium is incorporated into the bulk (formation of KMn 4 O 8 or KMn 8 O 16 ), the correlation was not found. The presence of NO in the gas mixture leads to a systematic decrease of soot ignition temperature for all samples.

A series of potassium-promoted spinels (Mn, Fe, Co) were prepared with various K ? promoter locations: on the surface (surface promotion) or in the bulk (formation of new layered and tunneled nanostructures via solid state reaction). All prepared samples were characterized by means of X-ray diffraction, Raman spectroscopy, X-ray fluorescence and N 2 -BET specific surface area analysis. Catalytic activity in soot combustion in different reaction conditions was investigated (tight contact, loose contact, loose contact with NO addition). It was shown that in all cases the nanostructuration is more effective than the surface promotion, with the layered structures of KCo 4 O 8 , KMn 4 O 8 being the most catalytically active phases, lowering the soot combustion down to 250°C. The difference in activity between tight and loose contacts can be bridged in the presence of NO due to its transformation into NO 2 , which acts as the oxygen carrier from the catalyst surface into soot particles, eliminating the soot-catalyst contact difference.

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The effect of surface and bulk potassium promotion on the transition metal oxides (Mn, Fe, Co) catalytic activity in catalytic soot oxidation was investigated. The surface promotion was obtained via incipient wetness impregnation, whereas the bulk promotion-nanostructuration-was obtained via wet chemical synthesis or solid state reaction leading to mixed oxide materials. The introduction of potassium into the transition metal oxide matrix results in the formation of tunneled or layered structures, which enable high potassium mobility. The structure of the obtained materials was verified by powder X-ray diffraction and Raman spectroscopy and the catalytic activity in soot oxidation was determined by TPO-QMS and TGA. It was found that the surface promotion does not alter the metal oxide structure and leads to either enhancement (Mn, Fe) or deterioration (Co) of the catalytic activity. Simultaneously, the catalytic activity in soot combustion of the potassium structured oxides is strongly enhanced. The most active, cobalt oxide based catalyst significantly lowers the temperature of 50 % of soot conversion by *350°C comparing to the non-catalyzed process. The study allows for the establishment of rational guidelines for designing robust materials for DPF applications based on ternary metal oxides.