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

Article abstract of DOI:10.1002/chem.201702248

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, (Fe^IICo^II)_2/3Fe^III_1/3(OH)₂(CO₃)_1/6?m H₂O, 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∥[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.

Full text of DOI:10.1002/chem.201702248

A Journal of
Accepted Article
Title: Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a
Layered Double Hydroxide Precursor and their Application in
Oxidation Catalysis
Authors: Klaus Friedel Ortega, Sven Anke, Fatih Özcan, Soma
Salamon, Jsutus Heese, Corina Andronescu, Joachim
Landers, Heiko Wende, Wolfgang Schuhmann, Martin Muhler,
Thomas Lunkenbein, and Malte Behrens
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201702248
Link to VoR: http://dx.doi.org/10.1002/chem.201702248
Supported by

10.1002/chem.201702248
Chemistry - A European Journal
COMMUNICATION
Topotactic Synthesis of Porous Cobalt Ferrite Platelets from a
Layered Double Hydroxide Precursor and their Application in
Oxidation Catalysis
Klaus Friedel Ortega,[a] Sven Anke,[b] Soma Salamon,[c] Fatih Özcan,[a] Justus Heese,[a] Corina
Andronescu,[d] Joachim Landers,[c] Heiko Wende,[c] Wolfgang Schuhmann,[d] Martin Muhler,[b] Thomas
Lunkenbein,*[e] and Malte Behrens*[a,f]
Abstract: Monocrystalline, yet porous mosaic platelets of cobalt
ferrite, CoFe2O4, can be synthesized from layered double
propene. Moreover, the OER activity of the ex-LDH catalyst was
markedly higher compared to the commercial material.
a
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 ñ 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
Cobalt ferrite, CoFe2O4, is a highly interesting compound due its
ferrimagnetic properties,[1] (electro-)chemical reactivity[2] and
catalytic activity.[3] For example, recent reports have highlighted
the potential of cobalt ferrite as component in multiferroic
ceramics,[4] as electrode material in Lithium batteries,[5] and as
water oxidation catalyst in electrolysis.[6] Cobalt ferrite is a
hopping semi-conductor and crystallizes in an inverse spinel
structure, which, due to its cubic symmetry is highly isotropic.
The typical habitus of spinel-type crystals are small (truncated)
octahedra or cubes. All of the above-mentioned applications can
be affected by the morphology and/or size of the cobalt ferrite
crystals possibly leading to small diffusion paths,[7] stable
magnetic suspensions,[8] or exposure of distinct crystal facets. It
is thus interesting to control the size and shape of cobalt ferrite
crystals during its synthesis. Size control of ferrites has been
practiced for instance by micelle approaches leading to small
crystallite sizes, but typically isotropic shapes.[9]
One effective way to manipulate the shape of oxide particles is
their synthesis through the mild thermal decomposition of an
anisotropic precursor compound. Oxide particles can be
obtained as pseudo-morphs of the decomposable precursor.
Important examples are layered double hydroxides (LDH), also
called hydrotalcite-like materials. LDHs typically crystallize in
form of thin hexagonal platelets due to their 2D layered crystal
structure and can be easily synthesized with carbonate anions
[a]
Dr. Klaus Friedel Ortega, Fatih Özcan, Justus Heese, Prof. Dr.
Malte Behrens
Faculty of Chemistry and Center for Nanointegration Duisburg-
Essen (CENIDE)
University of Duisburg-Essen
Universitätsstr. 7, 45114 Essen, Germany
E-mail: malte.behrens@uni-due.de
Sven Anke, Prof. Dr. Martin Muhler
Laboratory of Industrial Chemistry
Ruhr-University Bochum
[b]
[c]
[d]
[e]
by co-precipitation. Carbonate-LDH have the general
III
composition MII
M
x(OH)2(CO3)x/2ñmH2O. They consist of
1-x
Universitätsstr. 150, 44801 Bochum, Germany
Soma Salamon, Dr. Joachim Landers, Prof. Dr. Heiko Wende
Faculty of Physics and CENIDE
brucite-like layers MII/III(OH)2 with edge-sharing MO6 octahedra.
The excess positive charges of the MIII cations are compensated
by the carbonate anions in the inter-layer space, where also the
crystal water molecules reside. Upon mild calcination of an LDH
precursor, the anions decompose at moderate temperature and
the resulting oxide particles often retain the anisotropic platelet
morphology irrespective of the usually preferred habitus. LDHs
can incorporate many different M2+ and M3+ cations and are
widely applied in materials chemistry[10] and catalysis,[11] for
instance as basic catalysts,[12] electrocatalysts,[13] catalyst
precursor materials,[14] or flame retardants.[15]
University of Duisburg-Essen
Lotharstr. 1, 47057 Duisburg, Germany
Corina Andronescu, Prof. Dr. Wolfgang Schuhmann
Analytical Chemistry – Center for Electrochemical Sciences (CES)
Ruhr-Universität Bochum
Universitätsstr. 150; 44780 Bochum, Germany
Dr. Thomas Lunkenbein
Department of Inorganic Chemistry
Fritz-Haber-Institut der Max-Planck-Gesellschaft
Faradayweg 4-6, 14195 Berlin, Germany
E-mail: lunkenbein@fhi-berlin.mpg.de
Prof. Dr. Malte Behrens,
Ertl Center for Electrochemistry and Catalysis
Gwangju Institute of Science (GIST)
123 Cheomdan-gwagiro (Oryang-dong), Buk-gu, Gwangju 500-712,
South Korea
[f]
Generally, the formation of a phase-pure spinel from a single
LDH precursor is hindered by the compositional incompatibility
between precursor and target compound. Stable LDHs require a
MII/MIII ratio between approximately 2:1 and 4:1 (0.20 ≤ x ≤ 0.33).
Spinels MIIMIII2O4, however, usually need a MII/MIII ratio of 1:2.
Thus, typically poorly crystalline mixtures of spinel and additional
Supporting information for this article is given via a link at the end of
the document.
1
This article is protected by copyright. All rights reserved.

10.1002/chem.201702248
Chemistry - A European Journal
COMMUNICATION
MIIO are obtained by LDH calcination, often in form of a
nanoscale composite of isotropic primary particles aggregated in
form of platelets as for example described in detail for
ZnO/ZnAl2O4 mixed oxides derived from Zn,Al-LDH.[16] Herein,
we report the formation of phase-pure cobalt ferrite from an
detected,[17] which might be a result of the instability of FeII
during the relatively long storage time between synthesis and
the Mössbauer measurements.
Upon calcination in air, all FeII is oxidized to FeIII, thus fully
changing the overall MII/MIII ratio from initially 2:1
([FeII+CoII]/[FeIII]) to 1:2 required for spinel crystallization
LDH-containing precursor precipitate in
a unique form of
monocrystalline, but porous platelets and demonstrate the
potential of this new material in the catalytic oxidation of alcohols
and water. By comparison with conventional commercial cobalt
ferrite, it is shown that the novel ex-LDH cobalt ferrite exhibits
unique and interesting properties.
In the proposed co-precipitation synthesis, the above-mentioned
compositional constraint was overcome by using a mixture of
Fe2+ and Fe3+ for the synthesis of the LDH precursor at constant
pH value and under the exclusion of air (Fig. S1). The target
([CoII]/[2FeIII]). Calcination at 873
K leads to a complete
decomposition of the precursor (Fig. S4) and indeed yields a
phase-pure cobalt ferrite according to XRD (Fig. 1b). Based on a
Rietveld refinement of the calcined material, additional
crystalline phases can be excluded and the lattice parameter of
the CoFe2O4 was determined as 8.385(13) Å in good agreement
with the literature value and the spinel fraction in the precursor
(Fig. S5, Tab. S1, S2). Raman spectroscopy, which is highly
sensitive for hematite, also did not show any indication for the
presence of impurities (Fig. S6). The superparamagnetic
contribution has vanished from the room temperature
Mössbauer spectrum indicating CoFe2O4 crystallite sizes beyond
the superparamagnetic limit as a result of calcination (Fig. S3).
At low temperature and high field, the expected subspectra of
the spinel structure can be distinguished[18] due to a much lower
spin-canting compared to the precursor suggesting improved
crystallinity of CoFe2O4. Magnetometry shows the usual
behavior of CoFe2O4 with an increase in the saturation
magnetization and coercive field compared to the precursor
likely due to the increasing phase fraction and crystallinity as a
result of calcination (Fig S7).
composition
of
the
co-precipitate
was
FeII1/3CoII1/3FeIII1/3(OH)2(CO3)1/6ñmH2O in accordance with the
MII/MIII requirement of 2:1 (x = 0.33) for LDHs. The presence of
the LDH structure was confirmed by XRD, however a substantial
fraction of a spinel by-phase was also detected (Fig. 1a).
Rietveld refinement did not show any indication for an additional
phase (Tab. S1, S2). The phase composition was 45% LDH and
55% spinel. The lattice parameter of the spinel phase was
8.381(4) Å and thus very close to 8.3806 Å, a value expected for
CoFe2O4, (ICSD No. 98553) as compared to 8.0850 Å for Co3O4,
(ICSD No. 63165) or 8.3941 Å for Fe3O4 (ICSD No. 26410).
SEM investigation of the calcination product show the presence
of rather uniform aggregated platelets, which are pseudo-
morphs of the LDH precursor (Fig. 2a and Fig. S2b).
Interestingly, the SEM image clearly shows the presence of
intra-particular pores or holes in the individual platelets. These
likely have formed during the decomposition of the hydroxide
and carbonate anions leading to a shrinkage of the solid. Such
“slice of Swiss cheese” morphology is untypical for LDH
decomposition into mixtures of MIIMIII2O4 and MIIO in other
systems. While the retention of the platelet morphology is
common, shrinkage usually leads to a uniform size reduction of
the platelets, and not to the formation of holes. The specific
surface area of the ex-LDH CoFe2O4 amounts to 31 m2g-1 with
pore sizes between 2 and 38 nm in good agreement with Fig. 2
(Fig. S8). It is noted that the small particles assigned to the by-
phase are still seen as brighter spots in Fig. 2b, but in the SEM
images (Fig. 2a and S2b), they are no longer as clearly
observed after calcination, which might indicate that the smaller
nanoparticles have partially reacted with the larger cobalt ferrite
platelets upon heating to 873 K.
The HAADF-STEM image in Figure 2b shows the hexagonal
shape of a single platelet inherited from the LDH precursor with
the holes formed during decomposition and crystallization of the
spinel-type cobalt ferrite. Interestingly, high resolution (HR)TEM
and selected area electron diffraction (SAED) investigation
revealed that individual parts of the holey platelets, which are
not covered by spinel impurities are monocrystalline (Fig. 3). In
contrast, SAED patterns of aggregates of multiple platelets
appear polycrystalline. For single platelets that are covered by
spinel nanoparticles, additional spots arise in the otherwise
monocrystalline diffraction pattern (Fig. S9a,b). On the
nanoscale, the HRTEM images in Fig. 4 show that the porous
crystals are composed of a concerted arrangement of mosaic
block-like domains that are formed by aligned lattice defects.
a)
b)
Figure 1. XRD patterns and Rietveld fits of the precursor co-precipitate (a) and
of the calcined material (b). The co-precipitate consists of the phase-mixture of
45% LDH and 55% spinel. The calcination product is phase-pure CoFe2O4
(black: experimental data; red: calculated pattern; blue: difference;
orange/green: Bragg peak position of LDH/CoFe2O4).
We thus conclude that during co-precipitation, washing and
drying a significant amount of LDH has already been pre-
maturely transformed into the target spinel phase – likely a result
of the imperfect exclusion of air during the two latter steps.
Thorough washing was required to remove Na impurities below
a level of 0.05% as determined by AAS (see SI). SEM
micrographs of the co-precipitate further suggest the presence
of two different types of material. In addition to the platelet
particles of the LDH phase, which exhibit lateral sizes around
0.5-1 µm and a thickness of about a few tens of nanometers,
also smaller and roundish particles can be observed, tentatively
assigned to the spinel by-phase (Fig. S2a). Mössbauer spectra
of the precursor support the presence of CoFe2O4 (Fig. S3). In
addition to magnetically ordered CoFe2O4, a contribution of
superparamagnetic CoFe2O4 crystallites and/or FeIII from the
LDH was also detected. At low temperature and high field there
is complete magnetic ordering, but strong spin canting indicates
low crystallinity of the pre-maturely formed small CoFe2O4
particles. No clear indication of paramagnetic FeII was
2
This article is protected by copyright. All rights reserved.

10.1002/chem.201702248
Chemistry - A European Journal
COMMUNICATION
These defects add strain to the sample and may alter their
catalytic performance.[19]
crystallization from brucite-type Co(OH)2 precursors and found
to be highly interesting electrode materials for lithium ion
batteries.[21] We highlight that our synthesis procedure yields
binary mixed spinels and is based on the utilization of mixed
Fe2+ and Fe3+ solutions and that it should be generally applicable
for the synthesis of many kinds of ferrite spinels by combination
of Fe2+/Fe3+ with various LDH-forming cations M2+. For instance,
we have recently reported ex-LDH MgFe2O4 spinels as
precursors for Fe-based catalysts in ammonia synthesis and
decomposition.[22]
If
synthesized
from
a
FeII1/3Mg1/3FeIII1/3(OH)2(CO3)1/6ñmH2O LDH precursor, holey
platelets of the resulting MgFe2O4 can be found by SEM also in
this material (Fig. S10), showing the versatility of the proposed
synthesis approach.
Figure 2. SEM micrograph of the calcined LDH precursor showing aggregates
of porous platelets (a) and HAADF-STEM image of one individual platelet (b).
Careful inspection of the HRTEM images shows that the
crystalline orientation of the cobalt ferrite platelets remained
unchanged even when being interrupted by a pore hole (Fig. 4).
In addition, the pore edges as well as the 2D lattice defects are
oriented with respect to each other at distinct angles (e.g., 0°,
60° or 120°), which strengthens the picture of a monocrystalline
particle rather than a polycrystalline aggregate. Based on the
zone axis of the SAED and the indexing of the Fourier
Transform (FT) patterns (Fig. 3, insets), the viewing direction
perpendicular to the lateral dimensions is identified as [111] of
the spinel lattice for most crystals studied suggesting that 111
facets are the major surface termination. However, at one
occasion a [110] zone axis was also observed (Fig. S9c).
The majority of these observations indicate that the thermal
decomposition proceeds via a topotactical crystallization of the
cobalt ferrite, where the [111] zone axis is preferably related to
the c-axis of the LDH, which is the stacking axis of the layers
oriented perpendicular to the lateral dimensions of the platelets:
[111]Spinel||[001]LDH. A topotactic crystallization mechanism of
oxides formed from LDHs during calcination has been
proposed.[20] However, due to poor crystallinity and multiple
phases of the decomposition product, it turned out to be difficult
to establish a clear topotactic crystallization in a straightforward
manner for other LDH precursors.
We propose that the unique microstructure and morphology of
the ex-LDH CoFe2O4 is related to the successful pre-adjustment
of the cationic composition in the precursor. Using the LDH
approach, the cations are initially located in an atomically perfect
distribution in the solid solution type precursor. Upon oxidation of
FeII, also the proper ratio of MII/MIII is pre-adjusted throughout
the whole solid. Under these conditions, not met in conventional
LDHs without oxidizable FeII, crystallization of the CoFe2O4
requires hardly any solid-state diffusion of the cations and can
Figure 3. TEM image of a porous CoFe2O4 platelet (a) and corresponding
SAED pattern (inset), HRTEM image of the edge region of such a platelet (b)
and corresponding FT with indexing of the cubic spinel structure and zone axis
[111] (inset).
To demonstrate that the unique structural properties of the ex-
LDH CoFe2O4 are related to interesting chemical properties, we
here briefly introduce two application examples to compare the
new material to commercial CoFe2O4 (purchased from Sigma-
Aldrich). Cobalt ferrite is known as an oxidation catalyst showing
high activity, e.g., in the electrocatalytic oxygen evolution
reaction (OER),[23] in the gas phase oxidation of CO[3] or in the
selective oxidation of terpenes.[24] We have used the ex-LDH
CoFe2O4 and commercial CoFe2O4 in the temperature-
programmed oxidation of 2-propanol and in the OER. It is noted
that neither XRD nor N2 physisorption revealed major
differences in the crystallinity or specific surface area of the two
proceed readily in
a topotactic manner preferably under
retention of the orientation of the close-packed oxygen layers in
(001) in the trigonal LDH and (111) in the cubic spinel,
respectively. In particular, no phase segregation is required as a
single oxide phase can be formed. This easy crystallization of
the thermally stable spinel phase presumably leads to the early
formation of an oxide backbone in the typically not favored
anisotropic platelet form and to the formation of holey pores as
the anions decompose and H2O and CO2 diffuse out of the solid.
It is noted that mesoporous single crystals of spinel-type Co3O4
are accessible via
a closely related route by topotactic
3
This article is protected by copyright. All rights reserved.

10.1002/chem.201702248
Chemistry - A European Journal
COMMUNICATION
catalysts that could easily explain large differences in catalysis
(Fig. S8, S11).
Figure S9c and show high crystallinity not suggesting severe
surface segregation.
The results of the 2-propanol oxidation experiments are shown
in Figure 5 and Table S3. The commercial catalyst exhibits a
higher activity at low temperatures in the first heating cycle.
Upon cooling back down, however, the temperature profile of the
2-propanol conversion is very similar for both catalysts (gray
open symbols in Fig. 5) in agreement with the similar specific
surface area. It remained almost unchanged in further heating
cycles (Fig. S12). Interestingly, at 573 K the conversion in 2-
propanol is similar for both catalysts, while the oxygen
conversion and the product selectivity are markedly different.
The commercial material is highly selective to acetone indicating
that the oxidative dehydrogenation (1) is the major reaction over
this catalyst. This agrees with the conversion in oxygen reaching
similar values like that in alcohol. Contrarily, the major product
over the ex-LDH catalyst is propene (52% selectivity), indicating
that the dehydration reaction (2) is favored over this catalyst.
The selectivity to acetone was 40%, which corresponds roughly
to the conversion in oxygen. Only little total oxidation (3) was
observed in both cases and the extent was lesser for the ex-
LDH catalyst.
2 C3H7OH + O2
C3H7OH (+ O2)
2 C3H7OH + 9 O2
→
→
2 C3H6O + 2H2O
C3H6 + H2O
(1)
(2)
(3)
→
6 CO2 + 8 H2O
These findings suggest differences in acid-base or redox
properties of the cobalt ferrite surface in the two catalysts. The
dehydration activity of 2-propanol over metal oxides towards
propylene is affected by the number, the nature, and the
strength of acid sites.[25] In contrast, the dehydrogenation
pathway yielding acetone through a concerted mechanism over
acid-base pairs proceeds independent of their intrinsic strength.
Furthermore, the nature of the metal oxide and the carrier gas
type can modify the product selectivities.[26] In case of NiFe2O4,
significant differences in the product distribution have been
linked to variations in the Ni/Fe surface ratio.[27]
Figure 4. HRTEM image of a CoFe2O4 platelet showing a region with many
aligned lattice defects and the distorted hexagonal shape of the holey pores.
The zoom in the lower panel (b) shows the crystalline surrounding of one pore
and the undisturbed monocrystalline ordering at both sides of the hole
(compare FT 1 and 2).
The OER experiments for the ex-LDH and commercial CoFe2O4
are presented in Figure 6. The ex-LDH CoFe2O4 shows higher
catalytic activity towards OER, a current density of 10 mA cm-2
being reached at just 0.43 V overpotential, while for the
commercial CoFe2O4, 0.59 mV overpotential is required to reach
the same current density. Ex-LDH CoFe2O4 shows also a lower
Tafel slope (57 mV/dec) as compared with the commercial
material (128 mV/dec) which indicates that the electron transfer
is facilitated in the case of the ex-LDH material. The slope of the
current curve in Figure 6a suggests a higher conductivity of the
mono-crystalline platelets, which likely is an important
contribution
to
the
electocatalytic
activity.
Stability
measurements (Fig. S13) did not indicate decay of the activity or
severe structural changes of the particles at the electrode during
OER (Fig. S14).
For a full explanation of the different catalytic performances, a
detailed study of the surface chemistry is required, which is
beyond the scope of the present communication. In addition to
the preferred 111 termination and the unique morphology, also
alkaline residues such as surface OH groups or surface
segregation might play a role here. However, first HR scanning
TEM images of the surface region of the ex-LDH are shown in
Figure 5. Conversions (upper panels) and yields (lower panels) of the
commercial CoFe2O4 (left hand panels) and ex-LDH CoFe2O4 (right hand
panels) upon heating (closed symbols) and cooling (open symbols) in the
oxidation of 2-propanol as a function of temperature.
4
This article is protected by copyright. All rights reserved.

10.1002/chem.201702248
Chemistry - A European Journal
COMMUNICATION
[3]
[4]
[5]
[6]
[7]
[8]
[9]
C. A. Chagas, E. F. De Souza, M. C. N. A. De Carvalho, R. L. Martins,
M. Schmal, Applied Catalysis A: General 2016, 519, 139-145.
M. Etier, Y. Gao, V. V. Shvartsman, A. Elsukova, J. Landers, H. Wende,
D. C. Lupascu, Ferroelectrics 2012, 438, 115-122.
S. Permien, S. Indris, U. Schürmann, L. Kienle, S. Zander, S. Doyle, W.
Bensch, Chemistry of Materials 2016, 28, 434-444.
T. Grewe, X. Deng, H. Tüysüz, Chemistry of Materials 2014, 26, 3162-
3168.
In summary, the synthetic approach reported herein provides
access to porous ferrites with for well-crystalline spinels
relatively high porosity. In catalysis, such anisotropic materials
may bridge the gap between model catalysts with low surface
area and structurally highly complex real-world catalysts. They,
therefore, exhibit potential to contribute to
a
better
understanding in heterogeneous oxidation catalysis. To a first
approximation, the differences in catalytic properties reported
here seem to be best explained by different acid/base properties,
surface terminations and conductivity, but further work on these
questions is required, and is currently under way in our labs.
One specific aim is to fully control the topotacticity. In addition to
heterogeneous oxidation catalysis, these novel materials may
also play an important role in many other fields of materials
chemistry, in which ferrites are used, acting as a promising
materials basis for studying the role of particle anisotropy.[21d]
P. G. Bruce, B. Scrosati, J.-M. Tarascon, Angewandte Chemie 2008,
120, 2972-2989.
S. Amiri, H. Shokrollahi, Materials Science and Engineering: C 2013, 33,
1-8.
A. H. Lu, E. L. Salabas, F. Schüth, Angewandte Chemie - International
Edition 2007, 46, 1222-1244.
[10] a) D. G. Evans, X. Duan, Chemical Communications 2006, 485-496; b)
V. Rives, M. del Arco, C. Martín, Applied Clay Science 2014, 88-89,
239-269.
[11] C. Li, M. Wei, D. G. Evans, X. Duan, Small 2014, 10, 4469-4486.
[12] G. Fan, F. Li, D. G. Evans, X. Duan, Chemical Society Reviews 2014,
43, 7040-7066.
[13] F. Yang, K. Sliozberg, I. Sinev, H. Antoni, A. Bähr, K. Ollegott, W. Xia, J.
Masa, W. Grünert, B. R. Cuenya, W. Schuhmann, M. Muhler,
ChemSusChem 2017, 10, 156-165.
[14] a) M. Behrens, I. Kasatkin, S. Kühl, G. Weinberg, Chemistry of
Materials 2010, 22, 386-397; b) K. Mette, S. Kühl, H. Düdder, K. Kähler,
A. Tarasov, M. Muhler, M. Behrens, ChemCatChem 2014, 6, 100-104.
[15] A. Edenharter, P. Feicht, B. Diar-Bakerly, G. Beyer, J. Breu, Polymer
(United Kingdom) 2016, 91, 41-49.
a)
b)
[16] X. Zhao, F. Zhang, S. Xu, D. G. Evans, X. Duan, Chemistry of Materials
2010, 22, 3933-3942.
Figure 6. Linear sweep voltammograms (a) and Tafel slopes (b) of commercial
CoFe2O4 (red) and ex-LDH CoFe2O4 (black) recorded in O2-saturated KOH
(1 M) at a scan rate of 5 mV s-1 and 1600 rpm.
[17] L. Simon, M. François, P. Refait, G. Renaudin, M. Lelaurain, J.-M. R.
Génin, Solid State Sciences 2003, 5, 327-334.
[18] A. Bouhas, M. Amzal, B. Zouranen, Materials Chemistry and Physics
1993, 33, 80-84.
[19] K. Amakawa, L. Sun, C. Guo, M. Hävecker, P. Kube, I. E. Wachs, S.
Lwin, A. I. Frenkel, A. Patlolla, K. Hermann, R. Schlögl, A. Trunschke,
Angewandte Chemie International Edition 2013, 52, 13553-13557.
[20] a) D. G. Costa, A. B. Rocha, W. F. Souza, S. S. X. Chiaro, A. A. Leitão,
Journal of Physical Chemistry C 2012, 116, 13679-13687; b) S. Zhang,
Y. Dou, J. Zhou, M. Pu, H. Yan, M. Wei, D. G. Evans, X. Duan,
ChemPhysChem 2016, 2754-2766; c) L. Markov, K. Petrov, A.
Lyubchova, Solid State Ionics 1990, 39, 187-193.
Experimental Section
All experimental details are compiled in the supporting information.
Acknowledgements
[21] a) L. Tian, H. Zou, J. Fu, X. Yang, Y. Wang, H. Guo, X. Fu, C. Liang, M.
Wu, P. K. Shen, Q. Gao, Advanced Functional Materials 2010, 20, 617-
623; b) J. Wang, G. Du, R. Zeng, B. Niu, Z. Chen, Z. Guo, S. Dou,
Electrochimica Acta 2010, 55, 4805-4811; c) X. Duan, J. Ji, X. Yan, G.
Qian, D. Chen, X. Zhou, ChemCatChem 2016, 8, 938-945; d) D. Su, S.
Dou, G. Wang, Scientific Reports 2014, 4.
This work was supported by Stiftung Mercator (MERCUR) and
by the DFG within the SPPs 1681 (WE2623/7-1), 1613
(BE4767/2-2) and FOR 1509 (WE2623/13). We thank D.
Drescher, A. Servas, C. Stienen and A. Gehlhaar for their help
with the experimental work. Prof. S. Schulz, Prof. M. Epple and
Prof. M. Winterer of the University of Duisburg-Essen are
gratefully acknowledged for allocating access to their
characterization facilities.
[22] K. F. Ortega, D. Rein, C. Lüttmann, J. Heese, F. Özcan, M. Heidelmann,
J. Folke, K. Kähler, R. Schlögl, M. Behrens, ChemCatChem 2017, 9,
659-671.
[23] K. Chakrapani, G. Bendt, H. Hajiyani, I. Schwarzrock, T. Lunkenbein, S.
Salamon, J. Landers, H. Wende, R. Schlögl, R. Pentcheva, M. Behrens,
S. Schulz, ChemCatChem 2017, n/a-n/a.
Keywords: Cobalt Ferrite • Layered Double Hydroxide •
Topotactic Transformations • Selective Alcohol Oxidation •
Water Oxidation
[24] L. Menini, M. C. Pereira, L. A. Parreira, J. D. Fabris, E. V. Gusevskaya,
Journal of Catalysis 2008, 254, 355-364.
[25] A. Gervasini, A. Auroux, J. Catal. 1991, 131, 190-198.
[26] A. Gervasini, J. Fenyvesi, A. Auroux, Catal. Lett. 1997, 43, 219-228.
[27] R. Benrabaa, H. Boukhlouf, S. Barama, E. Bordes-Richard, R. N.
Vannier, A. Barama, Catal. Lett. 2012, 142, 42-49.
[1]
[2]
C. N. Chinnasamy, M. Senoue, B. Jeyadevan, O. Perales-Perez, K.
Shinoda, K. Tohji, Journal of Colloid and Interface Science 2003, 263,
80-83.
P. Lavela, J. L. Tirado, Journal of Power Sources 2007, 172, 379-387.
5
This article is protected by copyright. All rights reserved.

10.1002/chem.201702248
Chemistry - A European Journal
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Text for Table of Contents
Author(s), Corresponding Author(s)*
Page No. – Page No.
Title
6
This article is protected by copyright. All rights reserved.