Cordierite monolith-supported and powder Fe-K/Al 2 O 3 catalysts were prepared and thoroughly characterized by bulk (XRD, Raman spectroscopy, XRF, ICP-OES, TPR) and surface (XPS, IR, N 2-BET, NO x-TPD, K-TPD) sensitive methods. The catalytic activity was tested in TPO (temperature programmed oxidation) of model soot.

This paper describes the investigations of the catalytic activity in soot oxidation over well-defined iron oxide based materials. The nanostructuration of iron oxide by potassium into tunnelled (KFeO 2 ) and layered (K 2 Fe 22 O 34 ) ferrites and the surface promotion with CeO 2 results in the marked increase in the catalytic activity (decrease of the ignition temperature down to 210°C and T 10 % to 310°C). The measurements of the catalysts work function showed that both nanostructuration and surface promotion with ceria of the best KFeO 2 phase led to increase of the electron availability (decrease of the work function). Strong correlation of the catalytic activity in soot combustion of the Ce-K-Fe-O systems with the work function value was revealed for the first time in the model studies, and can be used as a guideline for optimisation of the real catalytic filters.

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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.