Synthesis and M?ssbauer spectroscopic investigation of copper-manganese ferrite catalysts for water-gas shift reaction and methanol decomposition

Article abstract of DOI:10.1016/j.materresbull.2017.06.019

Copper-manganese ferrites with nominal compositions Cu_1-хMn_хFe₂O₄, where x = 0; 0.2; 0.4; 0.6; 0.8 and 1 are synthesized by sol-gel auto-combustion method. Formation of ferrites with cubic spinel structure and crystallite size of 11–26 nm was observed. A decrease of iron located in tetrahedral positions with the increase of Mn content in ferrite structure was found. The prepared ferrite materials are tested as catalysts in water-gas shift reaction (WGSR) and methanol decomposition (MD). The samples are arranged according the WGS activity in following order: Cu_0.8Mn_0.2Fe₂O₄ > Cu_0.5Mn_0.5Fe₂O₄ > CuFe₂O₄ > Cu_0.2Mn_0.8Fe₂O₄ > MnFe₂O₄. All mixed copper-manganese ferrites exhibit higher catalytic activity in methanol decomposition as compared to single CuFe₂O₄ and MnFe₂O₄ ones. A significant phase transformation with ferrites under the reduction reaction medium which influences the formation of real catalytic active phase is registered. Formation of magnetite or Mn-substituted magnetite is registered during the WGSR, while iron carbides and Mn-rich oxides are the dominant phases during the MD reaction.

Full text of DOI:10.1016/j.materresbull.2017.06.019

Accepted Manuscript
Title: Synthesis and Mo¨ssbauer spectroscopic investigation of
copper-manganese ferrite catalysts for water-gas shift reaction
and methanol decomposition
Authors: Nikolay Velinov, Tanya Petrova, Izabela Genova,
Ivan Ivanov, Tanya Tsoncheva, Vasko Idakiev, Boris Kunev,
Ivan Mitov
PII:
S0025-5408(16)31440-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.materresbull.2017.06.019
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Accepted date:
12-10-2016
9-6-2017
13-6-2017
Please cite this article as: Nikolay Velinov, Tanya Petrova, Izabela Genova, Ivan
Ivanov, Tanya Tsoncheva, Vasko Idakiev, Boris Kunev, Ivan Mitov, Synthesis
and Mo¨ssbauer spectroscopic investigation of copper-manganese ferrite catalysts
for water-gas shift reaction and methanol decomposition, Materials Research
Bulletinhttp://dx.doi.org/10.1016/j.materresbull.2017.06.019
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Synthesis and Mössbauer spectroscopic investigation of copper-manganese ferrite
catalysts for water-gas shift reaction and methanol decomposition
Nikolay Velinov1*, Tanya Petrova1, Izabela Genova2, Ivan Ivanov1, Tanya Tsoncheva2, Vasko
Idakiev1, Boris Kunev1 and Ivan Mitov1
1 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
2 Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of
Sciences, 1113 Sofia, Bulgaria
*- corresponding author, e-mail address: nikivelinov@ic.bas.bg
Graphical abstarct
Cu1-xMnxFe2O4 after WGSR
x=0
Cu1-xMnxFe2O4 after MD
Cu1-xMnxFe2O4
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Velocity, mm/s
Highlights
-
Mössbauer spectroscopy reveals changes in cation distribution with Cu/Mn variation
partial reduction of Fe3+ to Fe2+ of the ferrites and formation of magnetite or Mn-
substituted magnetite is established after WGSR
-
-
Cu0.8Mn0.2Fe2O4 exhibits highest activity and stability in WGSR

-
-
more reductive medium formed during MD was found to lead to further reduction of
Mn-substituted magnetite phases to χ-Fe5C2 and Mn-reach oxides
Cu1-xMnxFe2O4 reveal higher catalytic activity in MD compared to CuFe2O4 and
MnFe2O4
Abstract
Copper-manganese ferrites with nominal compositions Cu1-хMnхFe2O4, where x=0; 0.2; 0.4;
0.6; 0.8 and 1 are synthesized by sol-gel auto-combustion method. Formation of ferrites with
cubic spinel structure and crystallite size of 11–26 nm was observed. A decrease of iron
located in tetrahedral positions with the increase of Mn content in ferrite structure was found.
The prepared ferrite materials are tested as catalysts in water-gas shift reaction (WGSR) and
methanol decomposition (MD). The samples are arranged according the WGS activity in
following order: Cu0.8Mn0.2Fe2O4>Cu0.5Mn0.5Fe2O4>CuFe2O4>Cu0.2Mn0.8Fe2O4>MnFe2O4.
All mixed copper-manganese ferrites exhibit higher catalytic activity in methanol
decomposition as compared to single CuFe2O4 and MnFe2O4 ones. A significant phase
transformation with ferrites under the reduction reaction medium which influences the
formation of real catalytic active phase is registered. Formation of magnetite or Mn-
substituted magnetite is registered during the WGSR, while iron carbides and Mn-reach
oxides are the dominant phases during the MD reaction.
Keywords: A. oxides, B. chemical synthesis, C. Mössbauer spectroscopy, D. catalytic
properties
1. Introduction

Spinel ferrites can be classified as normal spinel, inverse spinel and partially inverse one
according to occupation of divalent and three-valent cations of tetrahedral and octahedral
coordinated positions of the crystal lattice. A normal spinel is when all divalent cations
occupy only tetrahedral sites, inverse – when all divalent cations occupy octahedral sites and
partially inverse – when divalent cations occupy partially tetrahedral and partially octahedral
sites. It is known, that different metal cations have preference to occupy differently
coordinated positions [1]. Different cation distribution of a ferrite with given chemical
composition can be obtained by applying of different methods or conditions of synthesis [2].
The cation distribution is known that have influence on functional properties of ferrites as
magnetic, optical, catalytic etc [3-6]. On the other hand, it has been established that in some
cases multi-component ferrites has better catalytic behaviour than single component ferrite.
For example, mixed Cu-Co ferrite and Cu-Zn ferrite materials have better catalytic activity in
methanol decomposition than CuFe2O4 and ZnFe2O4 [7-11].
Various spinel ferrite materials have been successfully synthesis by applying the auto-
combustion sol-gel technology [12-17]. Synthesis conditions affect the phase impurities, the
crystallinity and consequently the particle size, the agglomeration ability, which finally
reduces the specific surface area [12]. Materials with composition Cu0.5Mn0.5Fe2O4 have been
successfully prepared by auto-combustion method at different pH of solution. It has been
established that synthesis at low pH results on obtaining of ferrite materials with lowest
crystalline size and better catalytic activity in methanol decomposition [18].
The aim of the present work is to prepare mixed Cu1-xMnxFe2O4 ferrites, where 0 ≤ x ≤
1, and to study the cation distribution in the ferrite structure by Mössbauer spectroscopy, as
well as the phase transformations under the reductive reaction medium. Methanol
decomposition (MD) was used as a catalytic test, since recently methanol has gained a

considerable interest as renewable “reservoir” for safety storage and transport of hydrogen,
syngas or methane which could be released in case of need [19-21].
The catalytic behaviour of thus obtained materials was also studied in water-gas shift
reaction (WGSR). In the last decade WGSR has attracted enhanced interest among the
scientists regarding the clean hydrogen production as a “green” fuel for future energy
systems, especially fuel cells [22, 23]. The WGSR is usually carried out in two successive
stages with cooling between them to achieve the desired degree of CO conversion, because of
thermodynamic and kinetic limitations. The magnetite (Fe3O4) is the main active phase in Fe-
containing catalysts of the high temperature first stage, which performs at 350-450oC to
reduce CO content to 3-5%. The Cu-based catalysts are commonly used in the second stage at
200-250oC to further decrease the CO concentration to less than 1%.
Although the noble metal (Pt and Au containing) catalysts have very good activity in
WGSR, the high cost of these noble metals restricts their wide application. Now developing
of copper-based ferrite catalysts is a great challenge [24]. An example is CuFe2O4 that has a
crystal structure known as an inverse spinel therefore the iron atoms split between tetrahedral
and octahedral sites, while the copper ions occupy predominantly octahedral ones. Khan at al.
note in their paper [25] that the rapid electron hopping between Fe3+⇔Fe2+ in the Fe3O4
lattice system is essential to catalyse WGS reaction. Moreover magnetite materials substituted
with Cr, Mn, Co, Ni, Cu, Zn and Ce ions possess highly facile Fe3+⇔Fe2+ redox couple. It can
be concluded that Cu-containing substitute ferrite catalytic systems are very promising for
WGSR applications.
2. Materials and Methods
2.1 Synthesis

Copper-manganese ferrites with nominal compositions Cu1-хMnхFe2O4, where x=0; 0.2;
0.4; 0.6; 0.8 and 1 were prepared by auto-combustion sol-gel method using the procedure of
the lowest pH of the initial solution reported in [18]. Shortly, the experimental procedure was
as follows: the corresponding stoichiometric amount from the starting nitrate salts
Cu(NO3)2.3H2O, Mn(NO3)2.4H2O and Fe(NO3)3.9H2O was dissolved in distilled water at
room temperature and constant stirring; citric acid was added to the solution in a molar ratio
equal to the sum of the metal ions (Cu, Mn) and stirring was continued at 60oC; the water was
evaporated from the solution by heating and continuous stirring on a magnetic stirrer; the
auto-combustion process was performed by heating the samples in an oven at 150oC for one
hour. As-obtained samples were designated by Cu1-хMnхFe2O4-CA. The samples were further
thermally treated at heat treated at 300oC with a heating rate of 10оС/min and retention at the
reference temperature two hours (identified with Cu1-хMnхFe2O4-TS300).
2.2 Methods of characterization
Powder X-ray diffraction (XRD) analysis was carried out by TUR M62 diffractometer
with Co Kα radiation. The database ICDD-PDF2 was used for crystalline phase identification.
The average crystallites size (D), the degree of microstrain (e) and the lattice parameters (a) of
the ferrite phase in the samples were determined by PowderCell-2.4.
The Mössbauer spectra at room temperature (RT) and liquid nitrogen temperature
(LNT) was recorded by Wissel (Wissenschaftliche Elektronik GmbH, Germany)
electromechanical spectrometer working in a constant acceleration mode. A 57Co/Rh (activity
 10 mCi) source and -Fe standard were used. The spectra were fitted using CONFIT2000
software [26].
2.3 Catalytic experiments

The water-gas shift activity measurements were carried out in a flow reactor at
atmospheric pressure. The test of catalysts was conducted in the temperature range of 140–
300°C. The experimental conditions were: catalyst bed volume 0.5 cm3, space velocity 4000
h–1, partial pressure of water vapor 31.1 kPa and 5.02 vol. % CO in argon as reactant model
gas mixture. The measured catalytic activity was expressed in % of CO conversion. The
catalytic activity was recorded after establishing of the steady-state conversion conditions for
corresponding temperature.
Catalytic test in reaction of methanol decomposition was carried out in a fixed bed flow
reactor with methanol partial pressure - 1.57 kPa; 50 cm3 min-1 argon as a carrier gas and
0.055 g of catalyst. Temperature-programmed regime within the range of 80–500oC with
heating rate of 1oC min-1 was used. HP apparatus equipped with flame ionization and thermo-
conductivity detectors and PLOT Q column was used for on-line gas chromatographic
analyses.
3. Results and discussion
X-Ray patterns of synthesized samples are presented in Figure 1. Calculated structural
parameters of the spinel phase in samples are presented in Table 1. The results of analysis
show that a spinel phase is obtained in all samples even after auto-combustion step. CuFeO2
(PDF 74-1953), Cu (PDF 4-836), CuO (PDF 80-1916) and Cu2O (PDF 78-2076) are also
detected. Their relative part is the highest for the single CuFe2O4-CA sample and decreases
with the increase of manganese content in the samples. Note that for the mixed Cu-Mn ferrites
an increase of the spinel unit cell parameter and decrease of the average crystallites size is
observed and this tendency is better pronounced with the increase of Mn content. After
thermal treatment at 300oC the spinel phase still remains as dominant one, but concomitant

phases of CuFeO2, CuO and Cu2O, all of them in slightly higher amount as compare to the
CA analogues is detected.
The Mössbauer spectra of the samples obtained after auto-combustion and fitted
hyperfine parameters are presented in Figure 2a and Table 2, respectively. The sextet
components in the spectra are related to tetrahedral and octahedral coordinated Fe3+ ions in
the spinel structure. A third sextet is appear in CuFe2O4-CA spectrum besides Sx1 and Sx2
which can be related to mixed-valence iron ions with electron hopping between Fe3+ and Fe2+
ions [27, 28]. Wide width sextet lines corresponding to octahedral Fe3+ ions are observed in
the spectra of Mn-containing samples and therefore a fitting model with more than one
component for octahedral iron is used. This is due to different number tetrahedral Fe3+ near
neighbours of octahedral Fe3+ accomplishing superexchange interactions. Therefore, part of
Mn2+ and/or Cu2+ ions occupy tetrahedral positions in spinel lattice. It could be suggested that
these ions are Mn2+ because of their preferences to tetrahedral occupation [1]. This is
confirmed by decreasing of iron occupying tetrahedral positions with increasing of Mn
substitution in the ferrites (Table 2). It is observed slightly increased isomer shift of Sx3 of
Cu0.8Mn0.2Fe2O4-CA and Cu0.5Mn0.5Fe2O4-CA spectra, which indicates a presence of mixed-
valence iron in octahedral coordination. The doublet components in the spectra of Mn
containing samples can be related to finely dispersed spinel particles with superparamagnetic
behaviour, excluding samples CuFe2O4 and Cu0.8Mn0.2Fe2O4 where the doublets have
hyperfine parameters of CuFeO2 [29]. Note that the doublet part in the spectra significantly
increases for MnFe2O4 and Cu0.2Mn0.8Fe2O4 materials and it is not influenced by the thermal
treatment procedure after the auto-combustion step.
The Mössbauer spectra of thermally treated samples are similar of these after auto-
combustion step (Figure 2b and Table 2). More significant differences are observed in the
spectra of CuFe2O4-TS300 and Cu0.8Mn0.2Fe2O4-TS300. Here a significant decrease and even

disappearance (for the former sample) of the sextet component assigned to iron in mixed
valence state (Sx3 in CuFe2O4-CA spectrum) as a result of Fe2+ oxidation is detected. This
observation is accompanied with simultaneous increase of the sextet components typical for
Fe3+ in spinel structure.
The Mössbauer spectra at liquid nitrogen temperature were measured for study of
doublet part of spectra. Decreasing of relative weight of the doublet components and
increasing of the sextet components compare to room temperature measurements is seen
(Figure 3 and Table 2). This confirms the presence of particles with superparamagnetic
behaviour in the samples with x ≥ 0.5.
The results from WGS catalytic activity tests of the samples prepared at 300oC from the
first day, when working phase was formatted, are presented in Figure 4a. During the first day,
the fresh catalysts, which are consisted of spinel ferrite and additional Cu-containing oxides
(Figure 1, Table 1) have activated in the course of the WGSR to metallic copper and
magnetite phases by controlled mild reduction in a stream of CO and H2O vapour. As can be
seen, the order of activity is Cu0.8Mn0.2Fe2O4 > Cu0.5Mn0.5Fe2O4 > CuFe2O4 >
Cu0.2Mn0.8Fe2O4 > MnFe2O4, because well-known properties of copper-based catalysts
exhibiting very high activity in low temperature WGSR (LT-WGSR). The second day results
(Figure 4b) show the same order of catalytic activity, but the degree of CO conversion in all
samples is reduced by 10-15%. One possible explanation is related to the difficult re-
oxidation of the surface because the adsorption of product of the reaction - CO2 and the
formation of carbonates. Another possible reason is the agglomeration, sintering of the most
finely dispersed metallic copper on the catalytic surface due to the previous day heating to
300oC in a reducing environment.
The higher catalytic activity of the mixed copper-manganese ferrites than that of single
copper and manganese ferrite could be due to the facilitated release of copper from the

structure of the ferrite in the presence of manganese. It is known that Cu2+ ions occupy
preferentially octahedral positions, as well as it have not been observed separate or additional
manganese phases outside of ferrite from XRD and Mössbauer data. Consequently, in the
mixed Cu-Mn ferrites the presence of manganese seems to assist the release of copper ions
from the ferrite lattice. The lower activity of Cu0.2Mn0.8Fe2O4 than that of pure copper ferrite
is most likely due to a low content of copper in the ferrite, which is not enough to demonstrate
high catalytic activity in LT-WGSR. The presence of additional copper phases in samples
with x ≥ 0.5 (Table 1) is not excluded to have a contribution to WGS activity.
Tested in water-gas shift reaction (WGSR) copper-manganese ferrites were studied with
Mössbauer spectroscopy (Figure 5). It is established transformation of the starting ferrite
phases accompanied with partial reduction of Fe3+ to Fe2+ and formation of magnetite in case
of CuFe2O4 and Mn-substituted magnetite in the case of manganese containing compositions
(Table 3). The spectra of Mn-substituted magnetite are fitted by model with more than one
sextet for octahedral coordinated iron because of the presence of different near-neighbor Mn
ions and different degree of reduction of Fe3+ to Fe2+. For the last can be concluded from
increasing of the isomer shift of the sextet lines. It is established that the increasing of the Mn
content in the samples leads to decreasing of the Fe2+ presence in the ferrite structure. Thus,
fast electron exchange between Fe3+ to Fe2+, which have been assumed as important for
WGSR, are limited by manganese content in the samples. This can be one of the reasons for
different catalytic activity in WGSR of Mn containing ferrites. A presence of doublet with
parameters of Fe2+ in wuestite is observed in the spectrum of the composition MnFe2O4.
In Figure 6 are presented temperature dependencies of methanol decomposition on
various ferrite materials. The change in the CO selectivity, which formation is directly related
to the ability of catalysts to release hydrogen from methanol, with the temperature increase is
shown in Figure 6. Methane (up to 5-6 %) and CO2 (up to 8-10 %) are also detected as by-

products for copper containing materials but their amount is extremely high in case of single
MnFe2O4. The conversion profiles exhibit complex shape with a plateau at 280-380oC and
next steep increase of the conversion with the temperature above 390-400oC for all copper
containing materials. For the latter, the conversion is initiated above 200-230oC and well
defined tendency for the increase in the catalytic activity with a decrease of copper content in
them is observed. The single ferrites, especially MnFe2O4-TS300, reveal lower catalytic
activity as compared to binary ones.
In order to understand the catalytic behaviour of the samples, Mössbauer spectra after
the catalytic test are collected (Figure 7). The observed changes in the Mössbauer spectra
reveal significant transformations with the initial metal oxide composition under the reaction
medium. The spectra of compositions 0 ≤ х ≤ 0.8 represent superposition of sextet
components with parameters (Table 4) typical for the different iron positions in the lattice of
Hägg carbide χ-Fe5C2 [30]. In addition to the sextet components in the samples with
composition х = 0.5 and х = 0.8 doublet with parameters of Fe3+ in paramagnetic oxide phase
is also detected. It is evident that sample MnFe2O4 undergoes least of all samples phase
transformation during catalytic reaction. The changes on this sample in result of reductive
reaction conditions are formation of wuestite with 22% relative weight of corresponding
doublet and increasing of the isomer shift of Sx2 and Sx3, which is related to partial reduction
of Fe3+ to Fe2+ in the spinel phase. Thus, in accordance with the Mössbauer and XRD data, the
complex catalytic behaviour of all samples with the increase of the reaction temperature could
be considered as a result of significant phase transformations with the primary ferrite and
copper oxide phases. For the single CuFe2O4-TS300 sample, a step-wise decomposition of
CuFe2O4 to metallic Cu and magnetite, which further transforms to carbide, is expected under
the reduction reaction medium. It can be presumed that the degree of the first step reduction
of initial samples in methanol decomposition test is similar to the reduction degree of the

samples after WGSR (Figure 5, Table 3). More reductive medium formed during methanol
decomposition was found to lead to further reduction of Mn-substituted magnetite phases to
iron carbides (χ-Fe5C2) and Mn-reach oxides. The doublet components in samples x ≥ 0.5 can
be refer to Mn-reach spinel ferrites. We can speculate that the improved catalytic properties
for all copper containing ferrites are provoked by the intimate contact between the copper
particles and various iron oxide phases. Stabilization of copper particles in highly dispersed
state over the iron species as well as the appearance of a synergic effect between them is
expected and this seems to be more pronounced when the copper particles are in contact with
iron-manganese ferrite phases.
4. Conclusions
The auto-combustion method is appropriate for synthesis of copper-manganese ferrites
type Cu1-хMnхFe2О4, where 0 ≤ х ≤ 1. The results of Mössbauer spectroscopy and XRD
analysis prove that a spinel phase with average crystallite size in the range of 11 – 26 nm is
obtained in all samples after auto-combustion and it is not observed significant increasing of
the size of crystallites after thermal treatment at 300oC. The spectra recorded at liquid
nitrogen temperature confirm the presence of particles with superparamagnetic behaviour in
the samples with x ≥ 0.5. Mössbauer analysis reveals that the increase of Mn substitution in
ferrites leads to a decrease in degree of occupation of tetrahedral positions with iron.
Copper-manganese ferrites show relatively high catalytic activity and stability in
WGSR and arranges according to their activity in followed order: Cu0.8Mn0.2Fe2O4 >
Cu0.5Mn0.5Fe2O4 > CuFe2O4 > Cu0.2Mn0.8Fe2O4 > MnFe2O4. All mixed copper-manganese
ferrites reveal higher catalytic activity compared to CuFe2O4 and MnFe2O4 in methanol
decomposition. The Mössbauer analysis of the samples after WGSR and MD evidences phase
transformation of initial ferrites under the influence of the reduction reaction medium. Partial

reduction of Fe3+ to Fe2+ and formation of stoichiometric magnetite in case of CuFe2O4 and
Mn-substituted magnetite in the case of manganese containing compositions is established
during WGSR. Predominantly iron carbides (χ-Fe5C2) and Mn-reach oxides are formed under
the highly reduction reaction medium during the methanol decomposition.
Acknowledgements
This work was supported by the National Science Fund [DFNI E02/2/2014].
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A. Gomez-Cortes, J. Bonifacio, G. Martinez-Barrerad, R. Perez-Hernandez, Int. J. Hydrogen
Energy 37 (2012) 9018–9027.
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233 (2005) 297–307.
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Spinel-cubic
Spinel-cubic
Cu
CuO
Cu2O
a)
CuO
b)
Cu2O
4000
3000
CuFeO2
3000
2000
1000
CuFeO2
2000
1000
CuFe2O4-CA
CuFe2O4-TS300
2500
2000
1500
1000
500
2500
2000
1500
1000
500
Cu0.8Mn0.2Fe2O4-CA
Cu0.5Mn0.5Fe2O4-CA
Cu0.8Mn0.2Fe2O4-TS300
2000
1500
1000
500
1500
1000
500
Cu0.5Mn0.5Fe2O4-TS300
Cu0.2Mn0.8Fe2O4-TS300
1400
1200
1000
800
1200
1000
800
600
600
Cu0.2Mn0.8Fe2O4-CA
MnFe2O4-CA
1200
1000
800
1200
1000
800
MnFe2O4-TS300
2
108
6
4
2
108
6
4
d, A
d, A
Figure 1. X-ray diffraction patterns of samples of
a) Cu1-хMnхFe2О4-CA and b) Cu1-хMnхFe2О4-TS300

a)
b)
1.00
0.98
0.96
0.94
0.92
0.90
1.00
0.98
0.96
0.94
0.92
CuFe2O4-TS300
CuFe2O4-CA
-10 -8
-10 -8
-10 -8
-6
-6
-6
-4
-2
0
2
4
6
6
6
6
6
8
8
8
8
8
10
10
10
10
10
-10 -8
-10 -8
-10 -8
-6
-6
-6
-4
-2
0
2
4
6
6
6
6
6
8
8
8
8
8
10
10
10
10
10
1.00
0.99
0.98
0.97
0.96
0.95
1.00
0.98
0.96
0.94
Cu0.8Mn0.2Fe2O4-TS300
Cu0.8Mn0.2Fe2O4-CA
-4
-2
0
2
4
-4
-2
0
2
4
1.00
0.98
0.96
0.94
0.92
1.00
0.98
0.96
0.94
Cu0.5Mn0.5Fe2O4-TS300
Cu0.5Mn0.5Fe2O4-CA
-4
-2
0
0
0
2
2
2
4
4
4
-4
-2
0
0
0
2
2
2
4
4
4
1.00
0.98
0.96
0.94
0.92
0.90
1.00
0.95
0.90
0.85
Cu0.2Mn0.8Fe2O4-CA
Cu0.2Mn0.8Fe2O4-TS300
-10 -8
-6
-4
-2
-10 -8
-6
-4
-2
1.00
0.95
0.90
0.85
1.00
0.95
0.90
0.85
MnFe2O4-CA
MnFe2O4-TS300
-10 -8
-6
-4
-2
-10 -8
-6
-4
-2
Velocity, mm/s
Velocity, mm/s
Figure 2. Mössbauer spectra of: a) Cu1-хMnхFe2О4-CA and b) Cu1-хMnхFe2О4-TS300

1.00
0.98
0.96
0.94
Cu0.5Mn0.5Fe2O4-TS300, LNT
0.92
1.00
-10 -8
-6
-4
-2
0
2
4
6
8
8
8
10
10
10
0.98
0.96
0.94
Cu0.2Mn0.8Fe2O4-TS300, LNT
-10 -8
-6
-4
-2
0
2
4
6
1.00
0.98
0.96
0.94
0.92
0.90
0.88
0.86
MnFe2O4-TS300, LNT
-10 -8
-6
-4
-2
0
2
4
6
Velocity, mm/s
Figure 3. Mössbauer spectra of Cu1-хMnхFe2О4-TS300 samples measured at LNT

a)
100
90
80
70
60
50
40
30
20
10
0
CuFe2O4-TS300
Cu0.8Mn0.2Fe2O4-TS300
Cu0.5Mn0.5Fe2O4-TS300
Cu0.2Mn0.8Fe2O4-TS300
MnFe2O4-TS300
Model gas equilibrium
140 160 180 200 220 240 260 280 300 320
Temperature, oC
b)
100
90
80
70
60
50
40
30
20
10
0
CuFe2O4-TS300
Cu0.8Mn0.2Fe2O4-TS300
Cu0.5Mn0.5Fe2O4-TS300
Cu0.2Mn0.8Fe2O4-TS300
MnFe2O4-TS300
Model gas equilibrium
140 160 180 200 220 240 260 280 300 320
Temperature, oC
Figure 4. Temperature dependence of the CO conversion in WGSR on different
Cu1-хMnхFe2О4-TS300 catalysts: a) as prepared, b) after first day test

1.00
0.95
0.90
0.85
CuFe2O4-TS300
-10 -8
-6
-4
-2
0
0
0
2
2
2
2
2
4
4
4
4
4
6
6
6
6
6
8
8
8
8
8
10
10
10
10
10
1.00
0.98
0.96
0.94
0.92
0.90
Cu0.8Mn0.2Fe2O4-TS300
-10 -8
-6
-4
-2
1.00
0.98
0.96
0.94
0.92
Cu0.5Mn0.5Fe2O4-TS300
-10 -8
-6
-4
-2
1.00
0.98
0.96
0.94
0.92
Cu0.2Mn0.8Fe2O4-TS300
-10 -8
-6
-4
-2
0
1.00
0.95
0.90
MnFe2O4-TS300
-10 -8
-6
-4
-2
0
Velocity, mm/s
Figure 5. Mössbauer spectra of Cu1-хMnхFe2О4-TS300 samples after WGSR

CuFe2O4-TS300
a)
Cu0.8Mn0.2Fe2O4-TS300
Cu0.5Mn0.5Fe2O4-TS300
Cu0.2Mn0.8Fe2O4-TS300
MnFe2O4-TS300
100
80
60
40
20
0
200 250 300 350 400 450 500
Temperature, oC
b)
100
80
60
40
20
0
CuFe2O4-TS300
Cu0.8Mn0.2Fe2O4-TS300
Cu0.5Mn0.5Fe2O4-TS300
Cu0.2Mn0.8Fe2O4-TS300
MnFe2O4-TS300
200 250 300 350 400 450 500
Temperature, oC
Figure 6. Temperature dependencies of conversion (a) and CO selectivity (b) in methanol
decomposition of thermally treated at 300oC ferrites

1.00
0.98
0.96
0.94
0.92
0.90
0.88
CuFe2O4-TS300
-10 -8
-10 -8
-10 -8
-10 -8
-10 -8
-6
-6
-6
-6
-6
-4
-4
-4
-4
-4
-2
-2
-2
-2
-2
0
0
0
0
0
2
2
2
2
2
4
4
4
4
6
8
10
1.00
0.98
0.96
0.94
0.92
0.90
0.88
Cu0.8Mn0.2Fe2O4-TS300
6
8
10
1.00
0.98
0.96
0.94
0.92
0.90
Cu0.5Mn0.5Fe2O4-TS300
6
8
10
1.00
0.98
0.96
0.94
0.92
0.90
0.88
0.86
Cu0.2Mn0.8Fe2O4-TS300
6
8
10
1.00
0.95
0.90
0.85
0.80
0.75
MnFe2O4-TS300
4
6
8
10
Velocity, mm/s
Figure 7. Mössbauer spectra of Cu1-хMnхFe2О4-TS300 samples after
methanol decomposition test
Table 1. Average crystallites size (D), degree of microstrain (e) and lattice parameter (a) of
the ferrite phase in samples determined from the experimental XRD profiles
D,
nm
e *103,
a.u.
a,
Å
Sample
CuFe2O4-CA
Cu0.8Mn0.2Fe2O4-CA
Cu0.5Mn0.5Fe2O4-CA
Cu0.2Mn0.8Fe2O4-CA
MnFe2O4-CA
Phase
Additional phases
Spinel 26.2
Spinel 15.8
Spinel 14.2
Spinel 11.4
Spinel 15.6
Spinel 27.1
Spinel 19.6
Spinel 14.2
Spinel 13.6
Spinel 15.6
2.12
2.69
2.95
1.01
9.07
1.74
1.54
2.94
9.59
8.40
8.37
8.41
8.45
8.44
8.49
8.35
8.38
8.42
8.42
8.53
CuFeO2, Cu, CuO, Cu2O
CuFeO2, Cu, CuO, Cu2O,
CuO
-
-
CuFe2O4-TS300
CuFeO2, CuO, Cu2O
Cu0.8Mn0.2Fe2O4-TS300
Cu0.5Mn0.5Fe2O4-TS300
Cu0.2Mn0.8Fe2O4-TS300
MnFe2O4-TS300
CuFeO2, CuO
CuO
-
-

Table 2. Mössbauer parameters of Cu1-хMnхFe2О4-CA and Cu1-хMnхFe2О4-TS300 (δ - isomer
shift, ΔEq - quadrupole splitting, B - effective internal magnetic field, Γexp - line widths, G -
relative weight of the partial components in the spectra, LNT- spectra measured at liquid
nitrogen temperature)
δ,
mm/s
ΔEq,
mm/s
B,
T
Γexp
mm/s
,
G,
%
Sample
Components
Sx1-Fe-tetra
0.31
0.00
49.7
0.45
24
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+, CuFeO2
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+, CuFeO2
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Db-Fe3+, CuFeO2
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+, CuFeO2
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
0.37
0.52
0.40
0.33
0.37
0.45
0.40
0.31
0.38
0.40
0.33
0.35
0.38
0.38
0.34
0.34
0.38
0.38
0.33
0.29
0.36
0.38
0.30
0.33
0.36
0.38
0.32
0.35
0.37
0.34
0.32
0.37
0.38
0.34
0.33
0.36
0.36
0.34
0.42
0.45
0.45
0.44
0.43
0.46
0.48
0.44
0.41
0.45
0.48
0.44
-0.05
-0.10
0.64
0.00
0.00
-0.04
0.66
0.00
0.02
-0.03
0.74
0.00
0.00
-0.05
0.83
0.00
0.02
-0.03
0.88
-0.01
-0.07
0.61
0.01
0.00
-0.11
0.63
0.00
0.00
-0.04
0.77
0.00
0.01
-0.04
0.86
0.00
0.01
-0.05
0.88
0.00
0.04
0.00
0.77
0.00
0.02
-0.05
0.93
0.00
0.02
0.05
0.94
51.7
46.6
-
49.5
46.9
43.0
-
47.4
44.6
40.6
-
45.7
42.2
37.5
-
45.4
41.3
35.3
-
48.2
50.0
-
46.4
48.5
42.4
-
48.0
45.6
42.1
-
46.7
43.2
38.7
-
44.5
41.1
33.3
-
49.9
51.6
47.2
-
49.5
51.4
44.7
-
0.54
0.93
0.29
0.51
0.61
1.17
0.31
0.46
0.65
1.19
0.52
0.64
0.81
1.19
0.58
0.80
0.90
0.90
0.56
0.53
0.47
0.30
0.56
0.51
1.12
0.35
0.53
0.56
1.13
0.55
0.61
0.76
1.38
0.60
0.79
1.02
0.96
0.59
0.52
0.41
0.84
0.50
0.61
0.47
1.61
0.66
0.72
0.51
1.39
0.62
50
21
5
28
29
37
6
17
34
41
8
14
31
17
38
14
17
7
62
51
43
6
34
41
19
6
33
24
36
7
21
24
20
35
15
14
6
CuFe2O4-CA
Cu0.8Mn0.2Fe2O4-CA
Cu0.5Mn0.5Fe2O4-CA
Cu0.2Mn0.8Fe2O4-CA
MnFe2O4-CA
CuFe2O4-TS300
Cu0.8Mn0.2Fe2O4-
TS300
Cu0.5Mn0.5Fe2O4-
TS300
Cu0.2Mn0.8Fe2O4-
TS300
MnFe2O4-TS300
65
46
27
22
5
35
27
18
20
20
20
10
50
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db-Fe3+
Cu0.5Mn0.5Fe2O4 –
TS300, LNT
Cu0.2Mn0.8Fe2O4-
TS300, LNT
48.3
50.6
41.7
-
MnFe2O4- TS300,
LNT

Table 3. Mössbauer parameters of Cu1-хMnхFe2О4-TS300 spectra after WGSR (δ - isomer
shift, ΔEq - quadrupole splitting, B - effective internal magnetic field, Γexp - line widths, G -
relative weight of the partial components in the spectra)
δ,
mm/s
ΔEq,
mm/s
B,
T
Γexp,
mm/s
G,
%
Sample
Components
Sx1-Fe-tetra, Fe3O4
Sx2-Fe-octa, Fe3O4
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Sx4-Fe-octa
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Sx4-Fe-octa
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Sx4-Fe-octa
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Sx4-Fe-octa
Db1-Fe3+
0.28
0.00
48.0
0.32
34
CuFe2O4-TS300
0.66
0.30
0.44
0.56
0.60
0.31
0.43
0.47
0.51
0.31
0.41
0.43
0.49
0.31
0.40
0.45
0.55
0.31
1.06
0.00
0.00
0.01
-0.03
0.01
0.00
0.01
-0.01
-0.01
0.00
0.03
-0.01
0.00
0.00
0.01
0.01
-0.08
0.56
0.59
44.9
47.6
46.2
44.3
41.3
47.6
45.3
42.9
39.3
46.9
44.3
41.7
37.8
48.0
46.2
44.2
41.2
-
0.56
0.36
0.49
0.58
0.96
0.38
0.48
0.57
1.02
0.42
0.60
0.68
1.22
0.37
0.46
0.66
0.94
0.67
0.47
66
25
16
31
28
19
23
28
30
13
28
33
26
14
13
25
21
10
17
Cu0.8Mn0.2Fe2O4-
TS300
Cu0.5Mn0.5Fe2O4-
TS300
Cu0.2Mn0.8Fe2O4-
TS300
MnFe2O4-TS300
Db2-Fe2+, wuestite
-

Table 4. Mössbauer parameters of Cu1-хMnхFe2О4-TS300 spectra after methanol
decomposition test (δ - isomer shift, ΔEq - quadrupole splitting, B - effective internal magnetic
field, Γexp - line widths, G - relative weight of the partial components in the spectra, LNT-
spectra measured at liquid nitrogen temperature)
δ,
mm/s
ΔEq,
mm/s
B,
T
21.6
Γexp,
mm/s
G,
%
38
Sample
Components
Sx1-χ-Fe5C2
0.26
0.10
0.36
CuFe2O4-TS300
Sx2-χ-Fe5C2
Sx3-χ-Fe5C2
Sx1-χ-Fe5C2
Sx2-χ-Fe5C2
Sx3-χ-Fe5C2
Sx1-χ-Fe5C2
0.20
0.21
0.26
0.22
0.20
0.24
0.20
0.23
0.40
0.24
0.21
0.24
0.39
0.32
0.52
0.67
0.48
1.07
0.03
0.08
0.10
0.02
0.05
0.09
0.03
0.04
0.94
0.08
0.02
0.01
0.95
0.00
-0.06
-0.05
0.87
0.78
18.9
11.2
21.6
19.2
11.1
21.4
19.1
11.2
-
21.4
19.0
11.3
-
0.52
0.32
0.35
0.51
0.36
0.36
0.49
0.32
0.62
0.37
0.49
0.33
0.65
0.41
0.56
0.75
0.93
0.48
48
14
37
48
15
36
38
10
16
32
33
8
27
18
13
11
36
22
Cu0.8Mn0.2Fe2O4-
TS300
Cu0.5Mn0.5Fe2O4- Sx2-χ-Fe5C2
TS300
Sx3-χ-Fe5C2
Db1-Fe3+
Sx1-χ-Fe5C2
Cu0.2Mn0.8Fe2O4- Sx2-χ-Fe5C2
TS300
Sx3-χ-Fe5C2
Db1-Fe3+
Sx1-Fe-tetra
Sx2-Fe-octa
Sx3-Fe-octa
Db1-Fe3+
49.4
47.1
43.8
-
MnFe2O4-TS300
Db2-Fe2+, wuestite
-