Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis

4 years ago

Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a Layered Double Hydroxide Precursor and Their Application in Oxidation Catalysis

Heiko Wende, Wolfgang Schuhmann, Malte Behrens, Martin Muhler, Justus Heese, Corina Andronescu, Joachim Landers, Fatih Özcan, Soma Salamon, Klaus Friedel Ortega, Thomas Lunkenbein, Sven Anke

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, (FeIICoII)2/3FeIII1/3(OH)2(CO3)1/6⋅m H2O, and the target spinel CoFe2O4 can be obtained in the precursor. During calcination, the remaining FeII fraction of the LDH is oxidized to FeIII 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∥[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. Topotactic: Porous, crystalline, mosaic platelets of the cobalt ferrite spinel, CoFe2O4, were synthesized by thermal decomposition of a layered double hydroxide precursor. Interesting chemical properties were observed compared to commercial spinel, and were demonstrated by 2-propanol oxidation catalysis and oxygen evolution reaction catalysis.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702248