Abstract
Iron-manganese oxide catalysts are known to influence the production of short chain hydrocarbons in the Fischer-Tropsch-synthesis process. XRD, XRF, gravity measurements and Mössbauer-effect spectroscopy has been used to study a catalytic precursor made by coprecipitation of iron and manganese oxides. The sample is characterized as a mixture of two compounds with the same iron to manganese ratio. The two compounds are cubic spinels with the same crystallographic parameters, however, one compound is a defect spinel while the other is not. In the Mössbauer studies the defect spinel shows superparamagnetic relaxation behavior—fluctuations of the magnetization vector along two opposite easy directions, while the non-defect spinel shows evidence of collective excitations—fluctuations of the magnetization vector in directions close to the easy direction. These properties are related to the particle sizes.
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Hearne, G.R., Pollak, H. Catalytic precursors: (Fe, Mn)3O4 and γ-(Fe, Mn)2O3 . Hyperfine Interact 67, 559–563 (1991). https://doi.org/10.1007/BF02398200
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DOI: https://doi.org/10.1007/BF02398200