Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

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.