Decomposition of mixed Mn and Co nitrates supported on carbon

Article abstract of DOI:10.1016/j.tca.2004.09.005

The effect of varying amounts of carbon support on the decomposition of mixed Mn and Co nitrates and the formation of spinel MnCo₂O ₄ is studied in this work. The molar ratios of the studied samples were n(Mn):n(Co):n(NO₃^-):n(C) = 1:2:6:Y and Y was varied from 0 to 25. IR and XRD measurements of the samples heated at various temperatures revealed spinel formation from the pure nitrates at 240°C but from the supported nitrates (Y = 15) already at 160°C. The spinel prepared from pure nitrates at temperatures ≤400°C was clearly non-stoichiometric. The supported nitrates produced a less non-stoichiometric spinel with smaller crystallite size. TG measurements revealed that compared with the pure nitrates, the decomposition of the supported nitrates initiated and was completed at lower temperatures. When carbon content was increased from Y = 0 to 20, the onset of the nitrate decomposition was shifted to lower temperatures. The increase of carbon amount beyond Y = 20 did not result in any considerable change. The decomposition of the supported nitrates was completed at temperatures 50-70°C lower than the pure nitrates. Both the decomposition of nitrates and the presence of spinel oxide enhanced the oxidation of carbon.

Full text of DOI:10.1016/j.tca.2004.09.005

Thermochimica Acta 427 (2005) 155–161
Decomposition of mixed Mn and Co nitrates supported on carbon
a,∗
b
a
c
¨
Terhi Nissinen , Markku Leskela , Michael Gasik , Jaakko Lamminen
a
Laboratory of Materials Processing and Powder Metallurgy, Helsinki University of Technology, P.O. Box 6200, FI-02015 HUT, Finland
b
Department of Chemistry, Laboratory of Inorganic Chemistry, P.O. Box 55, FI-00014 University of Helsinki, Finland
c
Laboratory of Applied Thermodynamics, Helsinki University of Technology, P.O. Box 4400, FI-02015 HUT, Finland
Received 6 July 2004; received in revised form 6 September 2004; accepted 9 September 2004
Available online 19 October 2004
Abstract
The effect of varying amounts of carbon support on the decomposition of mixed Mn and Co nitrates and the formation of spinel MnCo2O4
is studied in this work. The molar ratios of the studied samples were n(Mn):n(Co):n(NO3−):n(C) = 1:2:6:Y and Y was varied from 0 to 25. IR
and XRD measurements of the samples heated at various temperatures revealed spinel formation from the pure nitrates at 240 ◦C but from the
supported nitrates (Y = 15) already at 160 ◦C. The spinel prepared from pure nitrates at temperatures ≤400 ◦C was clearly non-stoichiometric.
The supported nitrates produced a less non-stoichiometric spinel with smaller crystallite size. TG measurements revealed that compared with
the pure nitrates, the decomposition of the supported nitrates initiated and was completed at lower temperatures. When carbon content was
increased from Y = 0 to 20, the onset of the nitrate decomposition was shifted to lower temperatures. The increase of carbon amount beyond
Y = 20 did not result in any considerable change. The decomposition of the supported nitrates was completed at temperatures 50–70 ◦C lower
than the pure nitrates. Both the decomposition of nitrates and the presence of spinel oxide enhanced the oxidation of carbon.
© 2004 Elsevier B.V. All rights reserved.
Keywords: MnCo2O4; Carbon; Supported nitrates; Thermogravimetry; Decomposition gases
1. Introduction
hydration degree of the nitrates [10], crystal size and support
[11], and the sample mass and the diameter of the crucibles
used in the measurements [10].
An interesting and feasible way to prepare small metal ox-
ide particles is to use carbon as a support for nitrate precur-
sors [1–4]. Our interest has been focused on the preparation of
spinel MnCo2O4, which has several applications, for instance
as catalysts for decomposition of NO and CO [5], reduction
of nitrogen oxides into N2 [6], and oxygen reduction reaction
[3,4,7,8]. For optimal preparation conditions it is essential to
know what factors affect the decomposition of the nitrate pre-
cursors. No detailed information on the decomposition of the
mixed Mn–Co nitrates was found in the literature, but sev-
eral reports for both the Mn and Co nitrates exist. Different
decomposition temperatures, mechanisms, and intermediates
are reported for the Mn and Co nitrates, depending on factors
such as heating rate, moisture content of the atmosphere [9],
In air or oxygen manganese nitrate decomposes up to
200–220 ◦C [10–14], and cobalt nitrate up to 240–280 ◦C
[11,12,15–17]. The decomposition of the nitrates can occur
simultaneously or after the water evaporation and its mech-
anism can be rather complicated. Transition metal nitrates
usually dehydrate below 180 ◦C followed by the decomposi-
tion of the anhydrous nitrate below 280 ◦C [12]. Mn [10]
and Co [11] nitrates have been reported to first lose wa-
ter followed by the decomposition of the anhydrous nitrate,
but also simultaneous water evaporation and nitrate decom-
position for Co-nitrate has been reported [17]. Formation
of different unstable intermediates has been reported, such
as MnO1.2(NO3)0.8 [13], MnONO3 [9], Co2(NO3)2(OH)2,
CoO·CoONO3, Co2ONO3 [14], and CoO and Co2O3 [17].
In moist atmosphere the decomposition of the nitrates can
occuratlowertemperaturesthanindryatmosphere[9]. More-
∗
Corresponding author. Tel.: +358 9 451 2777; fax: +358 9 451 2799.
E-mail address: terhi.nissinen@hut.fi (T. Nissinen).
0040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2004.09.005

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T. Nissinen et al. / Thermochimica Acta 427 (2005) 155–161
over, hydrated Mn nitrate has been reported to decompose at
lower temperatures than nearly dehydrated one [10]. The de-
composition of supported nitrates can be strongly affected by
the nature of the support. The results by Tiernan et al. [15]
show that, depending on the properties of the support, the
decomposition of the supported cobalt nitrate can either be
delayed or enhanced. Further, the crystal size of the nitrates
can affect the decomposition; Cseri et al. [11] have reported
that compared with the pure metal nitrates the decomposition
of metal nitrates supported on a clay started and was com-
pletedat0–40and5–105 ◦Clowertemperatures, respectively.
Since the decomposition shifted to lower temperatures pro-
nouncedly for the most amorphous nitrates, it was expected
that this shift was due to the small crystal size of the nitrates.
They also note that some decomposition steps that were ob-
served during the decomposition of pure nitrates were not
observed for the supported samples. The effect of varying
amounts of carbon support on the decomposition of the mixed
Mn and Co nitrates to form spinel MnCo2O4 is studied in this
report.
The samples for infrared (IR) and powder X-ray diffrac-
tion (XRD) studies were prepared with carbon contents of
Y = 0 and 15. The dried samples, 3 g for Y = 0 and 3.5 g
for Y = 15, were heated in air from room temperature up to
400 ◦C, at temperatures just below or above the temperatures
at which mass losses were observed in TG measurements,
or at 50 ◦C intervals. Each temperature was held for 30 min.
The crucibles containing the samples were covered with lids,
which were loose enough to allow gas exhaust but which pre-
vented loss of sample during the burning of carbon, which
initiated below 300 ◦C. IR measurements were recorded with
a Perkin-Elmer Spectrum GX with DTGS detector with res-
olution of 4 cm−1 and 64 scans, and the KBr pellets con-
tained 0.2 wt.% of the sample. XRD patterns were taken with
a Philips diffractometer with Cu K␣ as a radiation source,
using step size 0.02◦ and step time of 1 s.
3. Results
To be able to compare the results with varying amounts
of carbon, all TG results are normalised. In the mass scale
(Figs. 2,3 and 5), 100% corresponds to the mass of the
weighed hydrated nitrates with molar ratios of n(Mn):n(Co):
n(NO3−):n(H2O) = 1:2:6:16. The composition of MnCo2O4
corresponds to 28.4%.
2. Experimental
The molar ratios of the studied samples were
n(Mn):n(Co):n(NO3−):n(C) = 1:2:6:Y. Samples with Y = 0
(no carbon), 5, 10, 15, 20, and 25, were prepared by dis-
solving analytical grade nitrates Co(NO3)2·6H2O (Merck,
98.5%) and Mn(NO3)2·4H2O (Merck, 99%) in water. Aque-
ous solutions of the nitrates were mixed with varying amounts
of carbon powder (Ketjenblack®EC-300J, Akzo Nobel) hav-
ing a specific surface area of 950 m2 g−1. The samples were
dried at 40 ◦C in air.
The formation of the gaseous species during heating
of the nitrates was studied by thermogravimetry combined
with Fourier transformed infrared (TG–FTIR). Mass loss
was recorded by Perkin-Elmer Thermogravimetric Analyser
TG7. The measurements were carried out in air. The sample
masses were 22 (Y = 0) and 17 mg (Y = 20), and the heat-
ing rate was 10 K min−1. The TG analyser was coupled by
a heated transfer line to a 10 cm3 gas cell and Perkin-Elmer
System 2000 FTIR. The temperatures of the transfer line and
the gas cell were 186 and 190 ◦C, respectively. FTIR mea-
surements were made with resolution of 2 cm−1 and 16 scans
per slice.
The effect of varying carbon content on the decomposi-
tion of the mixed Mn–Co nitrates was studied by thermo-
gravimetry combined with differential scanning calorimetry
(TG–DSC). The measurements were carried out in a Netzsch
STA449C Jupiter analyser in air. The sample masses were
20–21 mg. While the heating rate of 10 K min−1 was found
feasible for TG–FTIR measurements in order to receive well
readable FTIR spectra, the heating rate of 5 K min−1 was
used in TG–DSC measurements in order to get more detailed
information on the decomposition steps.
3.1. Formation of gaseous species during decomposition
Fig. 1 shows the FTIR spectra of the gaseous species de-
veloped during the heating of the sample with Y = 20. The
strongest absorptions bands of NO2 and CO2 together with
TG curves for samples Y = 0 and 20 are plotted in Fig. 2. Dur-
ing drying at 40 ◦C part of the original water has evaporated.
That is why the mass of Mn–Co nitrate in the beginning of
the measurement is <100%. For the supported nitrates the
presence of carbon raises the starting point beyond 100%.
When Mn–Co nitrate (Y = 0) was heated in air, evapora-
tion of water had maximum rate around 200 ◦C and ceased
before 260 ◦C, which is before the maximum of NO2 forma-
tion. The formation of NO2 gas started soon above 200 ◦C,
had maximum at 270 ◦C, and ceased around 300 ◦C. In the
case of supported nitrates (Y = 20) the evaporation of water
had maximum rate at 140 ◦C and continued up to 220 ◦C si-
multaneously with NO2 formation, although started to slow
down when NO2 formation had reached the maximum. The
formation of NO2 started above 100 ◦C, had maximum at
190 ◦C and ceased around 230 ◦C. The comparison of sam-
ples Y = 0 and 20 reveals that for the supported nitrates the
decomposition initiated, had maximum, and ceased 100, 80,
and 70 ◦C earlier, respectively. While sample Y = 0 showed
NO2 formation with several steps, only one step was clearly
observable for Y = 20. This kind of fusing of the steps for
supported nitrates has been reported previously [11].
When carbon was studied alone with TG its burning did
not start before 550 ◦C in air. However, it is known that the

T. Nissinen et al. / Thermochimica Acta 427 (2005) 155–161
157
Fig. 1. FTIR spectra of gaseous species formed during heating of a supported Mn–Co nitrate with Y = 20, measured in air (10 K min−1).
presence of metals and metal oxides or formation of nitrogen
oxides can cause the oxidation of carbon at reasonably lower
temperatures [1,18]. This was observed in this work as well.
From the sample with Y = 20 the formation of CO2 due to
carbon oxidation started at 150 ◦C, had maximum at 300 ◦C,
and ceased around 450 ◦C (Fig. 2). A local maximum of CO2
formation at 200 ◦C was observed simultaneously with NO2
formation (Fig. 2). The highest oxidation rate of carbon, ob-
served at 300 ◦C, and another local maximum at 390 ◦C, are
observedclearlyafterthenitratedecomposition. Hence, itcan
be concluded that both the Mn–Co nitrate decomposition and
the presence of spinel oxide enhanced the carbon oxidation.
When Mn–Co nitrate is impregnated into high surface area
carbon powder, the materials seem to have a synergetic effect:
first, carbon reduces the decomposition temperature of the ni-
trates, and second, the metal nitrates and oxides facilitate the
oxidation of carbon.
As Fig. 1 illustrates for Y = 20, the absorption band at
1380 cm−1 (and also a weak band at 834 cm−1) is observable
till the end of the measurement with its maximum intensity.
This band appears soon after the onset of NO2 formatio−n,
and its frequency is very close to N O vibrations in NO3
.
In the case of Y = 0 as well this band remained till the end
of the measurement but was shifted to lower frequencies
(1350–1370 cm−1). While in the case of Y = 20 this band
is clearly less intensive than NO2 band (1630 cm−1), in
the case of Y = 0 it was clearly dominating being twice as
intensive as the NO2 band. Three additional absorptions
at 890, 1712, and 3568 cm−1 were observed around the
maximum formation of NO2 only for the sample Y = 0.
Thus, it seems that the composition of the NOx gases is
different for the pure nitrates and supported nitrates. Before
and after each measurement the IR-window was cleaned,
and it was noticed that during the measurement the colour
of the window had turned from transparent to yellowish.
These observations suggest that part of the reactants have
evaporated in connection with the nitrate decomposition
leading to the deposition of nitrates or the products of their
partial decomposition on the IR window. Similarly, Nohman
et al. [13] made IR gas phase analysis of various manganese
complexes and noted that analysis of manganese nitrate
was very difficult to perform owing to technical difficulties
arising from the brown colored gases of nitrogen oxides.
3.2. The effect of varying amounts of carbon
Although the prepared samples were dried at 40 ◦C
simultaneously for equally long time, the observations based
on sample mass recorded before and after drying showed
that the water content of the samples was not equal but
varied depending on the carbon content. After drying, the
water contents of the samples decreased almost linearly with
the increase in carbon content. Moreover, during weighing
Fig. 2. Mass losses of the Mn–Co nitrate (Y = 0) and supported Mn–Co
nitrate (Y = 20), measured in air (10 K min−1), and the absorbance of IR
bands for NO2 and CO2.

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T. Nissinen et al. / Thermochimica Acta 427 (2005) 155–161
Fig. 5. TG and DTG curves of Mn–Co nitrate supported on varying amounts
of carbon, measured in air (5 K min−1).
Fig. 3. TG and DSC curves of Mn–Co nitrate supported on varying amounts
of carbon, measured in air (5 K min−1).
surements suggest that the peak at 160 ◦C would be attributed
to water evaporation. The peaks between 180 and 210 ◦C are
probably associated with the simultaneous water evaporation
and nitrate decomposition, and the last peak at 240 ◦C to the
decomposition of anhydrous nitrate. Mass loss calculations
indicated that nitrates were mostly decomposed very soon
after this step, around 260 ◦C.
For the sample with Y = 5, DSC curve (Fig. 4) displays
three endothermic peaks at 50, 130, and 185 ◦C. Again, the
peak at 130 ◦C can be attributed to water evaporation and the
peak at 185 ◦C to the decomposition of the anhydrous nitrate.
Mass loss calculations indicated that nitrates were mainly
decomposed fairly soon after the latter peak, slightly above
200 ◦C. The slow mass loss after the nitrate decomposition
(Fig. 3)isprobablyattributedtoslowoxidationofcarbon. The
mass loss due to clearly exothermic carbon oxidation initiates
around 280 ◦C, has maximum at 330 ◦C and continues up to
400 ◦C.
Sample Y = 10 decomposed showing broad endothermic
DSC peaks at 130 and 165 ◦C (Fig. 4). For samples Y = 15
and 20 the latter peaks become still broader and are shifted to
lower temperatures. For Y = 20 the two peaks are nearly fused
together, indicating that water evaporation and nitrate de-
composition occur mostly simultaneously. The samples with
Y ≥ 10 display an additional mass loss step (Fig. 5) initiating
at 165–180 ◦C (depending on carbon content) and contin-
uing up to 210 ◦C. TG–FTIR measurements (Fig. 2) show
weak CO2 formation together with NO2 formation during
this step up to 230 ◦C (the delay by 20◦ is due to higher
heating rate). These data indicate that nitrates in the sam-
ples with Y ≥ 10 decompose first with simultaneous evap-
oration of water and then with simultaneous oxidation of
carbon. The mass loss due to carbon combustion initiates at
260–280 ◦C(Figs. 3and5), hasmaximumaround330 ◦C, and
continues up to 400–450 ◦C, the longer the higher the carbon
content.
of samples for the thermogravimetric measurements, the
samples either lost or absorbed moisture rapidly depending
on the prevailing humidity of air. As the molar ratios
of the metal ions, nitrate and carbon were known, the
water contents of the samples were determined from the
thermogravimetric data by assessing that the composition of
the samples is very close to MnCo2O4 at 700–900 ◦C. In the
beginning of the TG-DSC measurements, the samples where
n(Mn):n(Co):n(NO3−):n(C):n(H2O) = 1:2:6:Y:Z with Y = 0,
5, 10, 15, and 20 were estimated to have water contents
Z ≈ 13, 19, 15, 16, and 13, respectively. The TG–FTIR
samples with Y = 0 and 20 were assessed to have water
contents Z ≈ 12 and 10, respectively, in the beginning of the
measurements.
Figs. 3–5 show the TG, DSC, and DTG curves of Mn–Co
nitrate supported on varying amounts of carbon. Figs. 3 and 4
illustrate that the sample Y = 0 decomposes with several steps
showing endothermic DSC peaks. The peak around 50 ◦C is
attributed to melting. The observations from TG–FTIR mea-
Fig. 6 shows the temperatures of the maximum mass loss
rates attributed to nitrate decomposition, observed in DTG
(Fig. 5). The shifting of the maximum mass losses to lower
Fig. 4. DSC curves of Mn–Co nitrate supported on varying amounts of
carbon, measured in air (5 K min−1). At 30 ◦C, each curve has the value about
0 mW/mg. The curves have been lifted vertically to ensure the readability.

T. Nissinen et al. / Thermochimica Acta 427 (2005) 155–161
159
carbon. These are absorptions from C O and C O stretching
caused by oxygen functional groups on the surface of carbon
[19].
The bands at 825, 1385, and 2427 cm−1 in Fig. 7 originate
from the presence of nitrates. At 240 ◦C the intensity of the
nitrate band at 1385 cm−1 is considerably lower for Y = 15
than for Y = 0. Part of nitrate ions might be adsorbed on the
surface or trapped within the porous structure of the develop-
ing oxide [17]. The residual nitrate ions decomposed at lower
temperature (below 300 ◦C) from the supported samples than
from the unsupported samples, where the band at 1385 cm−1
is observed still at 350 ◦C.
Fig. 6. Peak positions of maximum mass loss rate vs. carbon molar content
Y, taken from the DTG data (Fig. 5).
The adsorption bands around 650–660 and 560–570 cm−1
correspond to metal–oxygen stretching in the spinel structure
[5,6,20]. For unsupported samples the formation of metal
oxide formation is observable not before 240 ◦C, but for
supported samples already around 160 ◦C. The same was
observed in XRD measurements.
The XRD reflections for the supported samples (Y = 15)
were less intensive and broader than for the unsupported sam-
ples. This is still observable in the samples heated at 400 ◦C
(Fig. 8). The sample prepared from the supported nitrates at
400 ◦C still contained ∼18 wt.% carbon as a support for the
formed spinel. These observations indicate that the nitrates
supported on carbon produce spinel particles with smaller
crystallite size than the unsupported nitrates. This can be ex-
plained by a confinement effect of the carbon pores: the small
pores of the carbon hinder the growth of the crystallised ni-
trate particles and the forming metal oxides within the pores
[1,2].
temperatures is almost linear as Y increases from 5 to 20, but
the increase from Y = 20 to Y = 25 does not show any clear
change. The shift to lower temperatures with the increase in
the carbon to nitrate ratio may be due to decreasing size of the
nitrate particles as well as to the interaction between nitrates
and carbon.
3.3. Formation of MnCo2O4 + δ
Fig. 7a and b show the IR spectra for the unsupported
(Y = 0) and supported (Y = 15) samples, respectively, heated
at temperatures up to 400 ◦C. The presence of water in the
samples is observed from the O H stretch and bend bands
at 3390–3430 and 1590–1630 cm−1. The samples contain-
ing nitrates were hygroscopic and exhibit strong bands at
these frequencies. The samples where most of the nitrates
already had decomposed during the heat treatment were non-
hygroscopic. Their water absorptions originate from KBr,
which absorbed moisture during the pellet preparation and
the measurement, and are shifted to higher frequencies com-
pared to nitrate-containing samples. Compared with the sam-
ples without carbon, water bands in the samples containing
carbon are slightly shifted to lower frequencies due to forma-
tion of C O H bonds [19]. Moreover, two additional bands
at 1723 and 1242 cm−1 are observed for samples containing
3.4. Non-stoichiometry
Preparation at low temperatures often produces non-
stoichiometric spinel MnCo2O4 + δ (JCPDS pattern 32–297),
which has smaller lattice parameter [7,21,22] than the sto-
ichiometric MnCo2O4 (JCPDS pattern 23–1237). For ex-
ample, preparations from nitrates at 400 ◦C [23] and at
250–500 ◦C [24], and from citrates and carbonates at 400 ◦C
Fig. 7. IR spectra after heat treatments of (a) Mn–Co nitrate (Y = 0) and (b) supported Mn–Co nitrate (Y = 15).

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T. Nissinen et al. / Thermochimica Acta 427 (2005) 155–161
Similar shifting of the metal–oxygen absorption bands to
higher frequencies has been observed with the decrease of
the calcination temperature to prepare MnCo2O4 [21,26] and
withtheincreaseoftheoxidationstateofmetalionsinvarious
metal oxides [20]. This suggests that the oxidation state of
the metal ions in the samples prepared in this work increases
in the order: preparation at 900 ◦C < 400 ◦C from supported
nitrates <400 ◦C from pure nitrates.
To make assessments of the non-stoichiometry, the sam-
ples heated at various temperatures were studied by TG-
measurements. The samples heated at 900 ◦C did not lose
mass before 1050 ◦C, where the decomposition of the spinel
into MnO and CoO initiated. This indicates that for this sam-
ple δ = 0. The sample prepared from pure nitrates at 400 ◦C
startedtonoticeablyloseweightaround460 ◦Cduetogradual
removal of oxygen. The calculations showed that the value
of δ for this sample was approximately 0.6. Assessment of δ
in the samples prepared from the supported nitrates was not
possible by TG. The remaining carbon content (∼18 wt.% at
400 ◦C) could not be measured with sufficient accuracy and
the carbon combustion at 300–500 ◦C occurred simultane-
ously with the reduction of the metal ions.
Fig. 8. XRD patterns after heat treatments of (a) Mn–Co nitrate (Y = 0) and
(b) supported Mn–Co nitrate (Y = 15). The vertical lines denote to reflection
positions of MnCo2O4.
[8,22] have produced MnCo2O4 + δ with δ = 0.6, 0.5–0.3, and
0.6–0.2, respectively. This kind of non-stoichiometry is ob-
served also for Co3O4+δ [16]. The cation deficiency possibly
induces the existence of OH− and H2O groups [23]. The
increase in the lattice constant between 300 and 1000 ◦C is
reported to be the consequence of the progressive reduction
of Co3+ to Co2+ and Mn4+ to Mn3+ [25]. The reduction of
Mn4+ to Mn3+ has also been observed when Mn nitrate was
decomposed first into MnO2, which was reduced into Mn2O3
at 500–560 ◦C [9,13].
For comparison, one sample was prepared at a higher tem-
perature without carbon and its preparation consisted of ini-
tial evaporation of water from the aqueous Mn–Co nitrate
solutions, decomposition of the nitrates at 250 ◦C for 2 h,
and calcination at 900 ◦C in air for 8 h. The XRD pattern of
this sample (Fig. 8) displays sharp reflections corresponding
to MnCo2O4, and intensive and relatively narrow reflections
indicate good crystallinity. The samples heated at tempera-
tures ≤400 ◦C show lower intensity and broader reflections
shifted to higher diffraction angles indicating formation of
smaller crystallites of non-stoichiometric MnCo2O4 + δ [24].
However, the shifting of the reflections is less pronounced in
the supported samples. The reflections of the sample prepared
by heating the supported nitrates at 160 ◦C were already at
lower diffraction angles than the reflections of the sample
prepared from pure nitrates at 240 ◦C or even at 400 ◦C. It
is probable that the oxidation of carbon has resulted in the
reduction of the metal ions and lower non-stoichiometry of
the spinel already at relatively low temperatures.
Approximations of δ were also done by comparing the po-
sitions of reflections (Fig. 8). The reflections of the sample
prepared from pure nitrates at 400 ◦C were fairly close to the
reflections of the samples with δ = 0.3–0.5 [24] and 0.6 [23],
prepared from nitrates at 270–500 and 400 ◦C, respectively.
Comparison of the reflection positions does not give an exact
value of δ, but it still indicates that δ must be higher than
0.3. The reflection positions of the samples prepared from
supported nitrates were between the positions of the sam-
ples with δ = 0.1 and 0.31 prepared from nitrates at 600 and
500 ◦C, respectively [24], and thus δ can be assessed to be
smaller than 0.3.
The values of δ were also assessed from the TG data of the
nitrates and supported nitrates. Because carbon was oxidised
up to 450 ◦C, the value of δ was assessed at 500 ◦C and was
found to be 0.34 for the sample with Y = 0 and 0.27 for the
sample with Y = 25. A clear decrease of δ from these values
was observed between 500 and 640 ◦C for the supported sam-
ples and between 570 and 640 ◦C for the unsupported sam-
ples. At 640 ◦C, δ was calculated to be 0.1 for both samples.
These observations indicate that for the unsupported samples
the reduction of metal ions occurs mainly between 570 and
640 ◦C, while for the supported samples the metal ions are
partly reduced already during the carbon combustion.
4. Conclusions
The molar ratios of the studied samples were
IR measurements showed the metal–oxygen stretching
bands at 629 and 543 cm−1 for the samples heated at 900 ◦C.
The spinel samples prepared at ≤400 ◦C (Fig. 7) show shift-
ing of these bands to ∼20 and 30 cm−1 higher frequencies
for supported (Y = 15) and unsupported samples, respectively.
n(Mn):n(Co):n(NO3−):n(C) = 1:2:6:Y.
When
mixed
Co–Mn nitrates (Y = 0) were heated in air, formation
of non-stoichiometric spinel MnCo2O4 + δ was observed at
240 ◦C. In the case of the supported samples (Y = 15) the
spinel formation was observed already at 160 ◦C. Further, the

T. Nissinen et al. / Thermochimica Acta 427 (2005) 155–161
161
supported nitrates resulted in a less non-stoichiometric spinel
than the pure nitrates. TG-measurements revealed that when
carbon content was increased from Y = 0 to 20, the onset of
the decomposition was shifted to lower temperatures and
the decomposition occurred more simultaneously with water
evaporation. The increase in the carbon content from Y = 20
to 25 did not result in any observable change. The nitrate
decomposition was mainly completed at 260–300 ◦C from
the pure nitrates, depending on the heating rate, and 50–70◦C
lower temperatures from the supported nitrates. Both the
decomposition of nitrates and the spinel oxide facilitated the
oxidation of carbon. Vigorous carbon combustion initiated
at 260–280 ◦C, had maximum at 330 ◦C and ceased after
450 ◦C.
[6] G.N. Pirogova, N.M. Panich, R.I. Korosteleva, Yu.V. Voronin, N.N.
Popova, Russ. Chem. Bull. 49 (9) (2000) 1536.
[7] A. Restovic, E. R´ıos, S. Barbato, J. Ortiz, J.L. Gautier, J. Electroanal.
Chem. 522 (2002) 141.
[8] M. Sugawara, M. Ohno, K. Matsuki, J. Mater. Chem. 7 (5) (1997)
833.
[9] P.K. Gallagher, F. Schrey, B. Prescott, Thermochim. Acta 2 (1971)
405.
[10] M. Maneva, N. Petroff, J. Therm. Anal. 36 (1990) 2511.
[11] T. Cseri, S. Be´ka´ssy, G. Kenessey, G. Liptay, F. Figueras, Ther-
mochim. Acta 288 (1996) 137.
[12] S. Yuvaraj, L. Fan-Yuan, C. Tsong-Huei, Y. Chuin-Tih, J. Phys.
Chem. B 107 (2003) 1044.
[13] A.K.H. Nohman, H.M. Ismail, G.A.M. Hussein, J. Anal. Appl. Py-
rolysis 34 (1995) 265.
ˇ
ˇ
ˇ
[14] Z.D. Zivkovic´, D.T. Zivkovic´, D.B. Grujicˇic´, J. Therm. Anal. 53
(1998) 617.
[15] M.J. Tiernan, E.A. Fesenko, P.A. Barnes, G.M.B. Parkes, M. Ronane,
Thermochim. Acta 379 (2001) 163.
Acknowledgements
[16] M. El Baydi, G. Poillerat, J.-L. Rehspringer, J.L. Gautier, J.-F.
Koenig, P. Chartier, J. Solid State Chem. 109 (1994) 281.
[17] S.A.A. Mansour, Mater. Chem. Phys. 36 (1994) 317.
[18] R. Turcotte, R.C. Fouchard, A.-M. Turcotte, D.E.G. Jones, J. Therm.
Anal. Calorim. 73 (2003) 105.
[19] R. Schlo¨gl, in: G. Ertl, H. Kno¨zinger, J. Weitkamp (Eds.), Handbook
of Heterogeneous Catalysis, VCH Verlagsgesellschaft mbH, Poitiers,
1997, pp. 138–191.
[20] J. Preudhomme, P. Tarte, Spectrochim. Acta 27A (1971) 961.
[21] T.V. Andrushkevich, G.K. Boreskov, V.V. Popovskii, L.M. Plyasova,
L.G. Karakchiev, A.A. Ostan’kovich, Kinet. Katal. 9 (6) (1968) 1244
(in Russian).
[22] J.M. Jime´nez Mateos, J. Morales, J.L. Tirado, J. Solid State Chem.
82 (1) (1989) 87.
¨
We are indebted to Dr. Ilkka Pitkanen for making the
TG–FTIRmeasurements, andMichaelFrimanformakingthe
TG–DSC measurements. We thank Nordic Energy Research
Program (subprogram Electrochemical Energy Conversion),
Fortum Foundation, Wihuri Foundation, and University of
Helsinki for financial support.
References
[1] M. Schwickardi, T. Johann, W. Schmidt, F. Schu¨th, Chem. Mater.
14 (2002) 3913.
[2] M. Ozawa, M. Kimura, J. Mater. Sci. Lett. 9 (4) (1990) 446.
[3] T. Nissinen, Y. Kiros, M. Gasik, M. Leskela¨, Chem. Mater. 15 (2003)
4974.
[23] J.L. Gautier, R. Fuentealba, C. Cabezas, Z. Phys. Chem. (Munich)
126 (1) (1981) 71 (in German).
[24] J.-F. Koenig, J. Brenet, C. R. Acad. Sci. B: Sci. Phys. 283 (3) (1976)
71 (in French).
[25] J.L.M. de Vidales, E. Vila, R.M. Rojas, O. Carc´ıa-Mart´ınez, Chem.
Mater. 7 (1995) 1716.
[4] T. Nissinen, Y. Kiros, M. Gasik, M. Lampinen, Mater. Res. Bull. 39
(2004) 1195.
[26] Q. Liang, K. Chen, W. Hou, Q. Yan, Appl. Catal. A 166 (1) (1998)
191.
[5] O.V. Sergeeva, A.M. Bol’shakov, G.A. Konin, L.V. Khmelevskaya,
Russ. J. Inorg. Chem. 44 (7) (1999) 1045.