Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 23, Issue 51, Pages 12443-12449Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201702248
Keywords
cobalt ferrite; layered double hydroxide; selective alcohol oxidation; topotactic transformations; water oxidation
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Funding
- Stiftung Mercator (MERCUR)
- DFG [WE2623/7-1, BE4767/2-2, WE2623/13]
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Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe2O4, can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe2+, Co2+, and Fe3+ during co-precipitation, a mixture of LDH, ((FeCoII)-Co-II)(2/3)Fe-1/3(III)(OH)(2)(CO3)(1/6)mH(2)O, and the target spinel CoFe2O4 can be obtained in the precursor. During calcination, the remaining Fe-II fraction of the LDH is oxidized to Fe-III leading to an overall Co2+:Fe3+ ratio of 1:2 as required for spinel crystallization. This pre-adjustment of the spinel composition in the LDH precursor suggests a topotactic crystallization of cobalt ferrite and yields phase pure spinel in unusual anisotropic platelet morphology. The preferred topotactic relationship in most particles is [111](Spinel)vertical bar[001](LDH). Due to the anion decomposition, holes are formed throughout the quasi monocrystalline platelets. This synthesis approach can be used for different ferrites and the unique microstructure leads to unusual chemical properties as shown by the application of the ex-LDH cobalt ferrite as catalyst in the selective oxidation of 2-propanol. Compared to commercial cobalt ferrite, which mainly catalyzes the oxidative dehydrogenation to acetone, the main reaction over the novel ex-LDH cobalt is dehydration to propene. Moreover, the oxygen evolution reaction (OER) activity of the ex-LDH catalyst was markedly higher compared to the commercial material.
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