Manganese-Iron Mixed Oxides of Spinel Structure as Soot Combustion Catalysts

Background: An abatement of emission of particulate matter (mainly soot) is a challenge for the scientific community. An active and cheap catalytic system for soot combustion can help solve this problem. Objective: The aim of this study was to investigate the influence of the composition of a series of Mn3-xFexO4 (x = 0 - 3) oxides of spinel structure on their catalytic properties in soot combustion. Methods: Samples were synthesized by coprecipitation followed by a consecutive thermal treatment. Their structure was verified by X-ray diffraction and Raman spectroscopy. The obtained catalysts were tested in model soot oxidation (Printex U) in both tight and loose contact modes. Results: It was found that different mechanisms of soot combustion occurred dependently on a chosen contact mode. Conclusion: It was confirmed that in the case of tight contact (TC), a coexistence of divalent manganese and iron species was decisive for the catalytic activity, whereas a presence of trivalent manganese centers was crucial in the case of loose contact (LC). Mn1.2Fe1.8O4 was found to be the most active catalyst.