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

Abstract

Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe O , can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe , Co , and Fe during co-precipitation, a mixture of LDH, (Fe Co ) Fe (OH) (CO ) ⋅m H O, and the target spinel CoFe O can be obtained in the precursor. During calcination, the remaining Fe fraction of the LDH is oxidized to Fe leading to an overall Co :Fe 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] ∥[001] . 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.

Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

“…The temperature corresponding to 50 % CO conversion (T 50 ) decreased from 273 to 188 K by substitution of 15 % Fe and remained similar up to 25 % Fe. Besides total oxidation, Co−Fe‐based spinel catalysts also showed excellent activity in selective oxidation, in particular of 2‐propanol in the gas phase [19–21] . For example, monocrystalline CoFe 2 O 4 synthesized by thermal decomposition of a layered double hydroxide was very active in dehydration yielding propene, while commercial CoFe 2 O 4 primarily catalyzed the oxidative dehydrogenation to acetone [19] .…”

“…Besides total oxidation, Co−Fe‐based spinel catalysts also showed excellent activity in selective oxidation, in particular of 2‐propanol in the gas phase [19–21] . For example, monocrystalline CoFe 2 O 4 synthesized by thermal decomposition of a layered double hydroxide was very active in dehydration yielding propene, while commercial CoFe 2 O 4 primarily catalyzed the oxidative dehydrogenation to acetone [19] . Further, Co 3 O 4 selectively catalyzed the oxidative dehydrogenation reaching nearly full conversion with 100 % selectivity to acetone at 430 K [21] .…”

Construction of stable core–shell imprinted Ag-(poly-o-phenylenediamine)/CoFe2O4 photocatalyst endowed with the specific recognition capability for selective photodegradation of ciprofloxacin

“…[43][44][45] CoFe 2 O 4 , as a widely used magnetic material, can be easily collected using a magnet without additional centrifugation or ltration and maintains a very good recyclability. [46][47][48][49][50][51] CoFe 2 O 4 can be used not only as a carrier to improve the specic surface area of composite materials, but also can reduce the costs to improve the economic viability of composite materials.…”

Continuous Hydrothermal Flow Synthesis of Co1–xNixFe2O4 (x = 0–0.8) Nanoparticles and Their Catalytic Properties for CO Oxidation and Oxygen Evolution Reaction

“…This material was synthesized by pH‐controlled (pH = 8.5) coprecipitation of a layered double hydroxide precursor followed by calcination at 600 °C for 3 h in air yielding CoFe 2 O 4 with a unique microstructure consisting of holely platelets. This material was recently shown to be a more active catalyst in the OER compared to commercial CoFe 2 O 4 and more selective to propene in the oxidative dehydration of 2‐propanol . However, it can be seen that at all temperatures the CO conversion rate was lower with this type of CoFe 2 O 4 particles.…”