Influence of Potassium and NO Addition on Catalytic Activity in Soot Combustion and Surface Properties of Iron and Manganese Spinels

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 KMn4O8 or KMn8O16), 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.