Nanosized copper ferrite materials: Mechanochemical synthesis and characterization

Article abstract of DOI:10.1016/j.jssc.2011.03.035

Nanodimensional powders of cubic copper ferrite are synthesized by two-steps procedure of co-precipitation of copper and iron hydroxide carbonates, followed by mechanochemical treatment. X-ray powder diffraction, Moessbauer spectroscopy and temperature-programmed reduction are used for the characterization of the obtained materials. Their catalytic behavior is tested in methanol decomposition to hydrogen and CO and total oxidation of toluene. Formation of nanosized ferrite material is registered even after one hour of milling time. It is established that the prolonging of treatment procedure decreases the dispersion of the obtained product with the appearance of Fe ₂O₃. It is demonstrated that the catalytic behavior of the samples depends not only on their initial phase composition, but on the concomitant ferrite phase transformations by the influence of the reaction medium.

Full text of DOI:10.1016/j.jssc.2011.03.035

Journal of Solid State Chemistry 184 (2011) 1153–1158
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Nanosized copper ferrite materials: Mechanochemical synthesis
and characterization
Elina Manova a, Tanya Tsoncheva b,n, Daniela Paneva a, Margarita Popova b, Nikolay Velinov a,
Boris Kunev a, Krassimir Tenchev a, Ivan Mitov a
a Institute of Catalysis, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 11, 1113 Sofia, Bulgaria
b Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113 Sofia, Bulgaria
a r t i c l e i n f o
a b s t r a c t
Article history:
Nanodimensional powders of cubic copper ferrite are synthesized by two-steps procedure of co-
precipitation of copper and iron hydroxide carbonates, followed by mechanochemical treatment. X-ray
powder diffraction, Mo¨ssbauer spectroscopy and temperature-programmed reduction are used for the
characterization of the obtained materials. Their catalytic behavior is tested in methanol decomposition
to hydrogen and CO and total oxidation of toluene. Formation of nanosized ferrite material is registered
even after one hour of milling time. It is established that the prolonging of treatment procedure
decreases the dispersion of the obtained product with the appearance of Fe2O3. It is demonstrated that
the catalytic behavior of the samples depends not only on their initial phase composition, but on the
concomitant ferrite phase transformations by the influence of the reaction medium.
Received 23 November 2010
Received in revised form
16 March 2011
Accepted 18 March 2011
Available online 22 March 2011
Keywords:
Mechanochemical synthesis
Copper ferrite
Mo¨ssbauer spectroscopy
Methanol decomposition
Toluene oxidation
& 2011 Elsevier Inc. All rights reserved.
1. Introduction
600 K and tetragonal one above 700 K. Jiang et al. [12] demonstrated
the predominant formation of CuFe2O4 with tetragonal unit cell
Transition metal spinel oxides are technologically important as
magnetic materials, semiconductors, pigments and as effective cata-
lysts for number of industrial processes, such as aluminum produc-
tion [1–4], oxidative dehydrogenation of butane to butadiene, two
step thermochemical methane reforming [5], hydrodesulphurization
of petroleum, photo-catalytic reactions [6], CO oxidation [7], treat-
ment of automotive exhausted gases [8], hydrogen production by
steam reforming of DME [9–11], etc. Copper ferrite is an inverse
symmetry if the sample is slowly cooled from high temperatures.
Nanosized spinel ferrites show unusual properties in comparison
with their bulk analogs and receive enormous attention during last
decade because of their potential applications [20–22]. They can be
obtained by variety of methods such as solid state reaction [23,24],
sol–gel [25], co-precipitation [23,25–27] and combustion synthesis
[28]. The use of ball-milling [1,12,13] is alternative synthesis route
with the preparation of material with particles in nanometer scale,
with high vacancy densities and variations in the site population.
The aim of the present work is to investigate the possibility of
CuFe2O4 nanodimensional powders synthesizing by co-precipita-
tion of the corresponding hydroxide carbonate followed by
mechanochemical treatment. The relationship between synthesis
parameters, phase composition, structural and catalytic proper-
ties of the obtained materials is studied. Methanol decomposition
to CO and hydrogen as well as total oxidation of toluene were
used as test reactions in order to follow the effect of the reduction
and oxidation reaction atmosphere, respectively, on the phase
transformations of the obtained spinel materials.
ferromagnetic spinel, which could be described as
a cubic
closed packed arrangement of oxygen ions with Cu2þ and Fe3þ
cations in tetrahedral (A) and octahedral (B) coordination. The cations
distribution in this structure can be represented by (CuxFe1ꢀx A
)
(Cu1ꢀxFe1þx)BO4, where x is the inversion parameter and x¼0 and
1 stands for the inverse and normal cases, respectively [12,13]. The
crystal symmetry and the properties of these ferrites are highly
sensitive to the cations distribution, which in turn depends on the
method of preparation. It was established that depending on the
preparation method, CuFe2O4 can crystallize either in tetragonal or
cubic symmetry [14,15]. Although the stable low temperature ferrite
phase is tetragonal, a deficit of Cu2þ cations in the B-sublattice leads
to the absence of cooperative Jan-Teller distortion and transformation
of crystal phase to cubic one [1,13–19]. Nedkov et al. [19] considered
the formation of cubic structure of CuFe2O4 at temperatures bellow
2. Experimental
2.1. Materials
The synthesis of copper ferrites was performed by two step
procedure, including (1) co-precipitation and (2) mechanical
milling of the co-precipitation precursors as it was described in
n Corresponding author.
E-mail address: tsoncheva@orgchm.bas.bg (T. Tsoncheva).
0022-4596/$ - see front matter & 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2011.03.035

1154
E. Manova et al. / Journal of Solid State Chemistry 184 (2011) 1153–1158
[29]. Co-precipitated hydroxide carbonates, which were used as
precursors were prepared from aqueous solutiuon of
Fe(NO3)3 ꢁ 9H2O and Cu(NO3)2 ꢁ 3H2O by dropwise addition of
1 M sodium carbonate up to pH 9 at continuous stirring. After
washing (until the absence of nitrates) and drying at RT, brown
substances are formed, denoted as CuFe(HC). The as-obtained
precursor powders were milled using a Fritsch Planetary miller
in a hardened steel vial together with grinding balls having
different diameters (from 3 to 10 mm). The precursors were
mechanically milled for 1, 2, 3 and 5h. Samples were denoted as
CuFe(x), where x corresponds to the duration of milling treatment
in hours.
CuFe2O4
α-Fe2O3
CuFe (5)
CuFe (3)
CuFe (2)
2.2. Methods of investigation
The powder XRD patterns were recorded by use of a TUR M62
diffractometer with Co Ka radiation. The observed patterns were
cross-matched with those in the JCPDS database. The room
temperature (RT) and liquid nitrogen temperature (LNT)
Mo¨ssbauer spectra were obtained with a Wissel (Wissenschaf-
tliche Elektronik GmbH, Germany) electromechanical spectro-
CuFe (1)
meter working in
(activity ffi10 mCi) source and a
a
constant acceleration mode.
-Fe standard were used. The
A
57Co/Cr
a
experimentally obtained spectra were fitted to mathematical
processing according to the least squares method. The parameters
of hyperfine interaction such as isomer shift (
splitting ( ), effective internal magnetic field (B), line widths
exp) and relative weight (G) of the partial components in the
d), quadrupole
D
(
G
CuFe (HC)
spectra were determined. Temperature-programmed reduction
(TPR) of the samples was carried out in the measurement cell of a
differential scanning calorimeter (DSC-111, SETARAM) directly
connected to a gas chromatograph (GC). Measurements were
made in the 300–973 K range at 10 K/min heating rate in a flow
of Ar:H2¼9:1, the total flow rate being 20 ml/min. A cooling trap
between DSC and GC removes the water obtained during the
reduction.
10
15
20
25
30
35
40
45
50
Co, Kα,Θ, deg
Methanol decomposition experiments were carried out in a
flow reactor using argon as a carrier gas, at methanol partial
pressure of 1.57 kPa and WHSV-1.5 hꢀ1. On-line gas chromato-
graphic analysis were performed on HP 5890 on PLOT Q column,
with simultaneous using of detector of thermo conductivity and
flame ionization detector and an absolute calibration method.
Toluene oxidation was studied at atmospheric pressure using a
fixed-bed flow reactor, air as carrier gas and 30 mg sample
(particle size 0.2–0.8 mm) diluted with 60 mg glass beads of the
same diameter previously checked to be inactive. The air stream
passed through a saturator filled with toluene and equilibrated at
273 K (ptoluene¼0.9 kPa). The activity was determined in the
temperature interval of 623–723 K at WHSV-1.2 hꢀ1. On-line
analysis of the reaction products were performed using HP-GC
with a 25 m PLOT Q capillary column.
Fig. 1. XRD patterns of hydroxide carbonate precursor and the materials obtained
after various milling duration.
Table 1
Average crystallites size (D), degree of microstrain (e) and lattice parameters (a)
determined from the experimental XRD profiles.
Sample
Phase
D (nm)
e  103 (a.u.)
˚
a (A)
CuFe(1)
CuFe(2)
CuFe(3)
CuFe(5)
CuFe2O4-cubic
CuFe2O4-cubic
CuFe2O4-cubic
CuFe2O4-cubic
7.4
9.2
8.0
9.9
10.31
9.87
9.62
5.64
8.39
8.39
8.39
8.38
[30] (Table 1). The obtained data indicate the increase of ferrite
crystal size in the range of 7–10 nm with about two fold decrease
of microstrain degree with increasing of treatment duration from
1 to 5 h. We should stress on the formation of impurities of
3. Results and discussion
3.1. Physicochemical characterization
crystalline a-Fe2O3 phase (PDF 79-1741) in the case of the
samples prepared after 3 and 5 h of milling.
XRD patterns of the obtained pair copper and iron materials
are presented in Fig. 1. Before the milling procedure only broad
reflections of hydroxide carbonate precursor, CuFe(HC), could be
In order to describe the state of iron containing phases more
precisely, Mo¨ssbauer spectra of the studied materials were
obtained (Fig. 2, Table 2). RT spectrum of CuFe(HC) sample
˚
distinguished. Well defined reflections of CuFe2O4 (a¼8.39 A, PDF
exhibits a quadruple doublet with d¼0.36 mm/s, D¼0.68 mm/s,
25-283) appear after 1 h of milling and a tendency of copper
ferrite crystallization during the prolonging of milling procedure
is observed. This assumption is well illustrated by the average
particles size and microstrain degree, determined from the
experimental XRD profiles by using the Williamson–Hall equation
indicating that the precursor is paramagnetic and the iron ions
are in trivalent oxidized state. RT Mo¨ssbauer spectra of all
materials after mechanochemical treatment represent doublets
and sextets. The parameters of the doublet components of
the spectra are typical of high spin Fe3þ ions in octahedral

E. Manova et al. / Journal of Solid State Chemistry 184 (2011) 1153–1158
1155
coordination. It could be assigned to the presence of ultra
dispersed iron containing particles with average size below 10–
12 nm, which relative part slightly decreases with the increasing
the environment of the Fe3þ ions after the milling procedure,
probably due to the formation of new ferrite phase. The sextet
component of the spectra is composed of two sextets with
of milling time (Table 2). The higher values of
materials (0.86–0.93 mm/s) in comparison with that one for the
precursor (0.68 mm/s) could be an indication for the changes in
D
for these
hyperfine field B¼48.2 and 45.1 T and isomer shifting d¼0.37
and 0.27 mm/s, respectively. They are generally assigned to Fe3þ
ions in octahedral and tetrahedral coordination in copper ferrite,
respectively ([12] and refs. therein). Their relative part increases
after 5 h of milling time indicating higher degree of ferrite
crystallization and agglomeration, which is in a good agreement
with the XRD results (see above). New sextet component with
relative weight G¼5% and parameters corresponding to Fe3þ ions
in hematite nanoparticles develops in the RT Mo¨ssbauer spectra
of the samples obtained after 3 and 5 h of milling. Since the MS
spectra of CuFe(1) and CuFe(2) do not contain lines typical of HC
precursor, the observed hematite phase with longer mechano-
chemical treatment could be assigned to the partial decomposi-
tion of CuFe2O4. In order to distinguish the iron species, which
represent doublet part of the RT Mo¨ssbauer spectra, LNT spectra
were also recorded. An increase of the sextet components with
parameters typical of hematite (11%) and copper ferrite (24–38%)
is registered. In addition to the typical Mo¨ssbauer parameter
100
95
100
95
90
CuFe(3)
CuFe(HC)
90
-10
-10
-5
-5
0
0
5
10
-10
-10
-5
-5
0
0
5
10
100
95
100
95
changes with the temperature (increased values of
d and B) a
90
CuFe(5)
preservation of the value of hematite is observed. This can be
D
CuFe(1)
90
100
98
explained by the small particle dimensions resulting in suppres-
sion of Morin’s transition. So, hematite nanoparticles seem to
be the main impurities of the obtained nanosized ferrite product,
which particles size increases with the milling duration.
5
10
5
10
100
96
The TPR profiles of all mechanochemically synthesized sam-
ples consist of two peaks (Fig. 3). The first sharp peak, appearing
at 490–500 K, could be ascribed to the reductions of CuFe2O4 to
metallic Cu and Fe2O3, and subsequent reduction of Fe2O3 to
Fe3O4 [9,11,31]. The high-temperature peak with maximum at
about 800 K is probably due to the reduction of Fe3O4 to Fe. The
shift of the reduction effects towards the temperature axes for the
various samples indicates some differences in their phase com-
position and particles size, as it was assumed also by XRD and
Mo¨ssbauer study (Figs. 1 and 2, Tables 1 and 2).
96
CuFe(5)
LNT
CuFe(2)
92
94
-10
-5
0
5
10
-10
-5
0
5
10
Velocity, mm/s
Velocity, mm/s
Fig. 2. RT Mo¨ssbauer spectra of hydroxide carbonate precursor and of mechan-
ochemically synthesized samples; for comparison-LNT spectrum of CuFe(5).
Table 2
Parameters of Mo¨ssbauer spectra of the investigated samples.
Sample
Components
D
(mm/s)
0.68
B (T)
Gexp (mm/s)
G (%)
d
(mm/s)
3þ
CuFe(HC)
CuFe(1)
Db-Fe
0.36
–
0.44
100
octa
3þ
Sx1-CuFe2O4–Fe
0.37
0.27
0.34
0.00
0.00
0.89
48.2
45.1
–
0.60
0.60
0.62
5
4
octa
3þ
Sx2-CuFe2O4–Fe
tetra
3þ
Db-Fe
91
octa
3þ
CuFe(2)
Sx1-CuFe2O4–Fe
0.37
0.27
0.34
0.00
0.00
0.86
48.2
45.1
–
0.60
0.60
0.57
5
6
octa
3þ
Sx2 -CuFe2O4–Fe
tetra
3þ
Db-Fe
89
octa
3þ
CuFe(3) RT
Sx1-
a
-Fe2O3–Fe
0.37
0.37
0.27
0.34
ꢀ0.10
0.00
49.8
48.2
45.1
–
0.60
0.60
0.60
0.66
4
8
octa
3þ
Sx2-CuFe2O4–Fe
octa
3þ
Sx3-CuFe2O4–Fe
0.00
8
tetra
3þ
Db-Fe
0.91
80
octa
3þ
CuFe(3) LNT
CuFe(5) RT
CuFe(5) LNT
Sx1-
a
-Fe2O3–Fe
0.42
0.47
0.37
0.43
ꢀ0.10
0.05
51.3
51.2
47.6
–
0.80
0.62
0.87
0.68
11
12
12
65
octa
3þ
Sx2-CuFe2O4–Fe
octa
3þ
Sx3-CuFe2O4–Fe
ꢀ0.02
0.92
tetra
3þ
Db-Fe
octa
3þ
Sx1-
a-Fe2O3–Fe
0.37
0.37
0.27
0.34
ꢀ0.10
ꢀ0.04
ꢀ0.05
0.93
50.3
45.9
44.1
–
0.43
0.54
0.82
0.71
5
9
octa
3þ
Sx2-CuFe2O4–Fe
octa
3þ
Sx3-CuFe2O4–Fe
10
76
tetra
3þ
Db-Fe
octa
3þ
Sx1-
a-Fe2O3–Fe
0.45
0.47
0.37
0.43
ꢀ0.10
0.00
51.9
51.0
47.4
–
0.80
0.62
0.90
0.85
11
19
19
51
octa
3þ
Sx2-CuFe2O4–Fe
octa
3þ
Sx3-CuFe2O4–Fe
0.00
tetra
3þ
Db-Fe
0.98
octa

1156
E. Manova et al. / Journal of Solid State Chemistry 184 (2011) 1153–1158
Table 3
Parameters of Mo¨ssbauer spectra of the investigated samples after the catalytic
test: t-total oxidation of toluene; M-methanol decomposition.
Sample
Components
d
D
B (T) Gexp
(mm/s)
G (%)
(mm/s)
(mm/s)
3þ
CuFe(3)_t
Sx1-
a
-Fe2O3–Fe
0.38
0.30
0.22
0.30
ꢀ0.10
ꢀ0.04
ꢀ0.01
0.82
51.3
48.4
45.4
–
0.35
28
27
38
7
octa
3þ
Sx2-CuFe2O4–Fe
0.62
0.93
0.62
octa
3þ
Sx3-CuFe2O4–Fe
tetra
3þ
Db-Fe
octa
CuFe(2)
CuFe(3)
3þ
CuFe(5)_t
Sx1-
a
-Fe2O3–Fe
0.38
0.32
0.23
ꢀ0.10
ꢀ0.04
0.00
51.8
48.5
45.3
0.35
0.64
1.02
30
31
39
octa
3þ
Sx2-CuFe2O4–Fe
octa
3þ
Sx3-CuFe2O4–Fe
tetra
3þ
CuFe(5)
CuFe(1)
CuFe(1)_M Sx1-Fe3O4–Fe
Sx2-Fe3O4–Fe
0.29
0.69
0.24
0.22
0.19
0.00
0.00
0.05
0.01
0.01
48.2
44.7
22.1
19.1
11.4
0.31
0.36
0.45
0.43
0.52
1
2
tetra
2,5þ
octa
Sx3-
Sx4-
Sx5-
w
w
w
-Fe5C2
-Fe5C2
-Fe5C2
35
36
26
300
400
500
600
700
800
900
Temperature, K
CuFe(2)_M Sx1-
w
w
w
-Fe5C2
-Fe5C2
-Fe5C2
0.26
0.22
0.18
0.05
0.01
0.01
22.0
18.9
11.2
0.45
0.52
0.49
37
37
26
Sx2-
Sx3-
Fig. 3. TPR profiles of mechanochemically synthesized materials.
3þ
CuFe(3)_M Sx1-Fe3O4–Fe
Sx2-Fe3O4–Fe
0.29
0.65
0.26
0.21
0.19
0.00
0.00
0.04
0.01
0.01
48.2
44.8
22.2
18.9
11.3
0.50
0.60
0.41
0.46
0.50
1
2
tetra
2,5þ
octa
Sx3-
Sx4-
Sx5-
w
w
w
-Fe5C2
-Fe5C2
-Fe5C2
31
39
27
100
80
60
40
20
0
3þ
CuFe(5)_M Sx1-Fe3O4–Fe
Sx2-Fe3O4–Fe
0.27
0.66
0.27
0.21
0.19
0.00
0.00
0.04
0.01
0.01
48.2
45.1
22.4
19.0
11.7
0.50
0.50
0.44
0.53
0.50
2
3
tetra
2,5þ
octa
Sx3-
Sx4-
Sx5-
w
w
w
-Fe5C2
-Fe5C2
-Fe5C2
32
38
25
CuFe(5)
CuFe(2)
CuFe(3)
CuFe(1)
occupation of the octahedral positions by Cu2þ ions. According
to [1,13–19], the increase of the population of the Cu2þ cations in
the B-sublattice provides the cooperative Jan-Teller distortion and
transformation of crystal phase to tetragonal one. This transfor-
mation is well illustrated by the XRD patterns of the samples after
the catalytic test, where both cubic and tetragonal ferrite phase
are registered (Fig. 7). According to [33], the increasing amount of
the octahedrally coordinated copper ions in the spinel structure,
which is observed after the catalytic test, could also facilitate the
catalytic process, due to the fact that the catalytic properties of
the spinel materials are mainly determined by the more exposed
to the surface octahedrally coordinated cations. So, the increase in
the reduction ability and the catalytic activity in toluene oxida-
tion is considered as a result of higher degree of crystallization of
a mixture of hematite, CuO and ferrite phase.
In Fig. 5 the temperature dependencies of methanol decom-
position on various materials are compared. On the contrary to
the catalytic behavior of the samples in the oxidative reaction
atmosphere, which exists during the toluene oxidation (Fig. 4),
here a complex conversion curves with a maximum at about
550 K and further conversion increase above 600 K, are observed.
The selectivity to CO is about 75–80% in a whole investigated
temperature interval with the formation of methane, CO2 and
dimethyl ether as by-products. The best catalytic activity is
registered for CuFe(5), which well corresponds with its high
reduction ability (Fig. 3). However the order of the catalytic
activity of the other samples does not follow their arrangement
in the reduction ability. After the catalytic test, RT Mo¨ssbauer
spectra of all materials (Fig. 6, Table 3) represent three sextets
with hyperfine field of about 22, 19 and 11 T, which are assigned
500
550
600
650
700
Temperature, K
Fig. 4. Temperature dependencies of toluene total oxidation for various mechan-
ochemically synthesized materials.
3.2. Catalytic study
The temperature dependencies of total oxidation of toluene for
various samples are presented in Fig. 4. For all materials the
conversion started above 520 K and about 100% combustion of
toluene to CO2 was achieved at about 620–630 K. We should
stress on the similarity of the catalytic behavior of the samples,
obtained under different milling time, despite the differences
observed in their initial phase composition (see above). The
sample CuFe(5) exhibits the best catalytic activity, which well
correlates with its reduction ability (Fig. 3). This result is not
surprising in a view of the data reported in the literature [32],
where Mars van Krevelen mechanism, including the release of
oxygen from the catalyst lattice, is generally discussed. The RT
Mo¨ssbauer spectra of the samples after the catalytic test (Table 3,
Fig.6) represent sextets of copper ferrite and about 30% a-Fe2O3 is
observed. This phase composition as well as the formation of
small amount of CuO nanoparticles is confirmed by the XRD
patterns of the used materials (Fig. 7). Comparing the phase
composition of the samples before and after the catalytic test
(Tables 2 and 3; Figs. 2 and 6), the intensive crystallization and
agglomeration of the spinel ferrite particles under the oxidative
reaction medium is assumed. Moreover, the changes in the
relative part of both sextet components in the Mo¨ssbauer spectra
after the catalytic test reveal an increase in the inversion para-
meter of the spinel lattice, which corresponds to higher
to the formation of new iron carbide (w-Fe5C2) phase [34]. With
the exception of the CuFe(2), the spectra of the other materials
consists of two additional sextets with parameters, corresponding
to Fe3O4 phase with relative part about 3–5%. These transforma-
tions of the initial iron containing phase are also confirmed by the
XRD patterns of the samples after the catalytic test (Fig. 7), where

E. Manova et al. / Journal of Solid State Chemistry 184 (2011) 1153–1158
1157
100
80
60
40
20
0
CuFe (5)_t
CuFe2O4-c
α-Fe2O3
CuF2O4-te
CuO
CuFe(1)
CuFe(3)
CuFe(5)
CuFe(2)
10
15
20
25
30
35
40
45
50
500
600
700
Temperature, K
CuFe (5)_M
100
80
60
40
20
0
Fe3O4
χ-Fe2C5
Cu
CuFe(1)
CuFe(3)
CuFe(5)
CuFe(2)
10
15
20
25
30
35
40
45
50
Co, Kα,Θ, deg
Fig. 7. XRD patterns of CuFe(5) sample after total oxidation of toluene (CuFe(5)_t)
and methanol decomposition (CuFe(5)_M).
500
600
700
Temperature, K
magnetite, iron carbide and metallic copper are registered. So, the
intensive processes of reduction and decomposition of the initial
ferrite phase occur by the influence of the reduction reaction
medium. Obviously, these phase transformations under the
reduction medium provides the observed complex catalytic
behavior of the studied ferrites with the temperature increase
and it is determined by the current ratio between the various
iron- and copper-containing active components, such as metallic
copper, ferrite, hematite, magnetite and iron carbide [35].
Fig. 5. Temperature dependencies of conversion and CO selectivity in methanol
decomposition for various mechanochemically synthesized materials.
100
99
4. Conclusions
98
The co-precipitation of copper and iron hydroxide carbonates
and their high-energy ball milling, facilitates the formation of
nanocrystalline copper ferrites with cubic crystal structure. The
phase composition of the obtained materials depends on the
milling duration. The catalytic properties of ferrites are strongly
influenced by their phase transformations under the reaction
medium. Predominantly agglomeration and further crystalliza-
tion of spinel ferrite nanoparticles occurs under the oxidation
reaction medium during the toluene oxidation. Almost total
transformation of ferrite phase to metallic copper, magnetite
and iron carbide is observed under the reduction reaction med-
ium, which realizes during the methanol decomposition and
facilitates the selective formation of hydrogen and CO.
97
CuFe (5)_t
-10
100
5
-5
0
10
98
96
94
CuFe (5)_M
-10 -5
0
5
10
Acknowledgments
Velocity, mm/s
Financial support of the National Science Fund of the
Bulgarian Ministry of Education and Science through projects
Fig. 6. Typical RT Mo¨ssbauer spectra of CuFe(5) sample after methanol decom-
position (CuFe(5)_M) and total oxidation of toluene (CuFe(5)_t).

1158
E. Manova et al. / Journal of Solid State Chemistry 184 (2011) 1153–1158
DO 02-295/2008, Rila 4-412 (DO 02-29/2008) and TK 02-63 is
acknowledged.
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