The carbon dioxide decomposition reaction with (NixCu1-x)Fe2O4 solid solution

Article abstract of DOI:10.1002/1521-396X(200202)189:3<741::AID-PSSA741>3.0.CO;2-J

The mechanisms of the redox reaction of (Ni_xCu_1-x)Fe₂O₄ solid solution were investigated by thermo-gravimetric analysis and X-ray diffraction experiments. The redox reaction was accelerated by a kind of a substituted divalent metal such as Ni and Cu. (Ni_xCu_1-x)Fe₂O₄ showed excellent reduction reaction with increasing Ni content and excellent CO₂ decomposition with increasing Cu content. The CO₂ decomposition ability of the reduced (Ni_xCu_1-x)Fe₂O₄ showed the maximum value at x = 0.5. CO₂ was decomposed by oxidation of oxygen deficient FeO (FeO_1-δ, 0 ≤ δ ≤ 1). The (Ni_0.5Cu_0.5)Fe₂O₄ solid solution is an excellent candidate for the practical application of the CO₂ decomposition.

Full text of DOI:10.1002/1521-396X(200202)189:3<741::AID-PSSA741>3.0.CO;2-J

phys. stat. sol. (a) 189, No. 3, 741–745 (2002)
The Carbon Dioxide Decomposition Reaction
with (Ni Cu )Fe O Solid Solution
x
1—x
2
4
1
H. C. Shin (a), J. H. Oh (b), J. C. Lee (c), S. H. Han (d), and S. C. Choi ) (a)
(
a) Department of Materials Science and Engineering, Ajou University, Suwon 442-749,
Korea
(
(
b) Department of Ceramic Engineering, Inha University, Inchon 402-751, Korea
c) Department of Inorganic Materials Engineering, Myongji University, Youngin 449-728,
Korea
(
d) Cleantech Center, Korea Institute of Science and Technology, Cheongryang P. O. Box 131,
Seoul 130-650, Korea
(
Received May 1, 2001; accepted September 30, 2001)
Subject classification: 61.50.Nw; 61.66.Fn; 64.75.þg; S11.2
The mechanisms of the redox reaction of (NixCu1 –– x)Fe2O4 solid solution were investigated by
thermo-gravimetric analysis and X-ray diffraction experiments. The redox reaction was accelerated
by a kind of a substituted divalent metal such as Ni and Cu. (NixCu1 –– x)Fe2O4 showed excellent
reduction reaction with increasing Ni content and excellent CO2 decomposition with increasing Cu
content. The CO2 decomposition ability of the reduced (NixCu1 –– x)Fe2O4 showed the maximum
value at x ¼ 0.5. CO2 was decomposed by oxidation of oxygen deficient FeO (FeO1 –– d, 0 ꢀ d ꢀ 1).
The (Ni0.5Cu0.5)Fe2O4 solid solution is an excellent candidate for the practical application of the
CO2 decomposition.
Introduction The decomposition of carbon dioxide (CO2) into carbon or carbon mon-
oxide (CO) has been one of the possible target technologies for the utilization of CO2
and the mitigation of greenhouse effects. Sacco and Reid reported the decomposition
of CO2 on clean steel wool [1]. Recently, Tamaura reported that oxygen-deficient M-
ferrites (M ¼ Ni, Mn, Zn, etc.) of the spinel structure were prepared by the reduction
of H2 (Eq. (1)), and the oxygen-deficient M-ferrites easily reduced CO2 into carbon [2–
9] (Eq. (2)):
MFe2O4 þ H2 ¼ MFe2O4 –– d þ d H2O,
MFe2O4 –– d þ CO2 ¼ MFe2O4 þ CO2 –– d .
(1)
(2)
They assumed the formation of oxygen deficient sites in M-ferrite by the H2 reduction
and the reversible phase change during the redox reaction. Herein, we found that the
reaction mechanisms of Eqs. (1) and (2) were not appropriate for the redox reaction of
M-ferrites [10]. In addition, we found that NiFe2O4 and CuFe2O4 showed excellent reduc-
tion reaction and CO2 decomposition, respectively. In this study, (NixCu1 –– x)Fe2O4 solid
solution was prepared and the redox reaction for CO2 decomposition was investigated.
Experimental NiCl2, CuCl2, and FeCl3 (First Grades, Kanto Chemical Co.) were used
for preparing (NixCu1 –– x)Fe2O4 (x ¼ 0.25, 0.5, and 0.75) by a coprecipitation of the
1)
e-mail: scchoi@madang.ajou.ac.kr
Corresponding author; Tel.: +82-31-219-2466; Fax: +8231-219-1610;
#
WILEY-VCH Verlag Berlin GmbH, 13086Berlin, 2002 0031-89 65 /02/18902-0741 $ 17.50 þ.50/0

742
H.C. Shin et al.: Carbon Dioxide Decomposition on (NixCu1 –– x)Fe2O4 Solid Solution
corresponding metallic chlorides. Aqueous solution of KOH (5 N) was added dropwise
to the solution of metallic chlorides maintaining pH 10. The reaction mixture was stir-
ꢁ
red at 80 C for 6h. The precipitate was filtered and washed with water and acetone
ꢁ
ꢁ
several times. The product was then dried at 100 C for 12 h and calcined at 800 C for
h. The ferrites were analyzed by XRD (McScience, M18SHF-SRA X-ray diffract-
ometer, CuKa), Cu-Ka, to monitor their structures.
NixCu1 –– x)Fe2O4 was reduced by 5% H2 in Ar in a Cahn vacuum electrobalance
system. The ferrite powder (50 mg) was placed in a platinum crucible in a quartz tube
2
(
(
1 inch outer diameter), and H2 was introduced at room temperature. The ferrite was
ꢁ
heated by a halogen lamp heater under H2 gas (60 ml/min) at the heating rate of 10 C/min
to 800 C. Gases was supplied by a gas distribution system with mass flow controllers
ꢁ
(Matheson Co.). After the reduction, the reduced ferrite was analyzed by XRD.
The decomposition of CO2 was performed with the same Cahn vacuum electroba-
lance system as the one of the reduction process. CO2 gas (60 ml/min) was introduced
ꢁ
ꢁ
into the system at the heating rate of 10 C/min to 800 C. The concentration change of
the product gas during CO2 decomposition reaction was analyzed by a quadruple mass
spectrometer. Ferrite structures were analyzed by XRD experiments after the decompo-
sition reaction.
Results and Discussion The XRD spectrum of (NixCu1 –– x)Fe2O4 after the calcination
showed a typical spinel structure. The reduction behaviors of (NixCu1 –– x)Fe2O4 were
investigated by TGA experiments. The reduction of ferrites was monitored by the
weight loss (Fig. 1). The weight decreased to form reduced ferrite as the temperature
ꢁ
ꢁ
increased to 800 C. The weight loss of (Ni0.25Cu0.75)Fe2O4 was observed from 250 C,
ꢁ
but the weight loss of (Ni0.5Cu0.5)Fe2O4 and (Ni0.75Cu0.25)Fe2O4 occurred at 100 C high-
er than the temperature at which reduction of (Ni0.25Cu0.75)Fe2O4 did. In the reduction
ꢁ
reaction of (NixCu1 –– x)Fe2O4 to 800 C, the weigh loss of (Ni0.25Cu0.75)Fe2O4,
(Ni0.5Cu0.5)Fe2O4, and (Ni0.75Cu0.25)Fe2O4 were 19%, 21%, and 22%, respectively. The
reduction patterns of (NixCu1 –– x)Fe2O4 did correspond to the NiFe2O4 which performed
a one-stage reduction [10]. In the result of Fig. 1, it was found that starting temperature
of the reaction and total weight loss of (NixCu1 –– x)Fe2O4 was increased with increasing
Ni content in (NixCu1 –– x)Fe2O4.
Fig. 1. TGA curves of the reduction of
(
(
(
NixCu1 –– x)Fe2O4: (a) (Ni0.25Cu0.75)Fe2O4,
b) (Ni0.5Cu0.5)Fe2O4, and
c) (Ni0.75Cu0.25)Fe2O4.
Experimental
conditions: 5% H2 in Ar, heating rate
ꢁ
1
0 C/min, and flow rate 60 ml/min

phys. stat. sol. (a) 189, No. 3 (2002)
743
There are four oxygen atoms in each ferrite, which has the spinel structure. When x
is 0 to 1, the total weight percentage of oxygen atoms in (NixCu1 –– x)Fe2O4 is 26.7% to
2
7.2%, respectively. So, the weight loss of about 20% meant that three oxygen atoms in
ꢁ
(NixCu1 –– x)Fe2O4 were eliminated, leaving only one oxygen atom behind at 800 C. The
elimination of three oxygen atoms from the ferrite generated FeO along with metallic
Cu or Ni and Fe. The formation of FeO, metallic Ni or Cu and Fe were further con-
firmed by XRD.
ꢁ
As the reduction temperature increased to 800 C, a phase change of (NixCu1 –– x)Fe2O4
was observed in the XRD spectrum (Fig. 2). Phases of reduced (Ni0.25Cu0.75)Fe2O4 were
ꢁ
a-Fe, FeO and Cu. At 800 C, there was a 20% weight loss in the TGA experiment,
which was equivalent to the loss of three oxygen atoms. The elimination of three oxy-
gen atoms from (Ni0.25Cu0.75)Fe2O4 should give a mixture of Cu, FeO, and a-Fe phases.
ꢁ
In the (Ni0.5Cu0.5)Fe2O4 and (Ni0.75Cu0.25)Fe2O4 reduced up to 800 C, the spinel struc-
ture disappeared, generating metallic Fe–Ni and some FeO due to a decrease over
20% of total weight by the H2 reduction.
The important point to note is that the metallic Cu and a-Fe phases existed as sepa-
rate ones in the reduced (Ni0.25Cu0.75)Fe2O4 compared with forming a Ni–Fe alloy in
the reduced (Ni0.75Cu0.25)Fe2O4. In the metallic state of Ni and Fe, Ni dissolved into Fe
to form a stable isomorphous system of Ni–Fe phase. However, in the metallic state of
Fe and Cu, the alloy formation was inhibited in the presence of the miscibility gap, and
Fe and Cu existed as separated phases [11].
The CO2 decomposition reactions were performed by introducing 99.9% CO2 into
ꢁ
the reduced (NixCu1 –– x)Fe2O4 which were reduced up to 800 C with 5% H2 in Ar. The
weight changes were monitored by TGA experiments (Fig. 3). With the temperature
increasing, CO2 oxidized with the reduced ferrites and supplied oxygen to the reduced
ferrite producing carbon and CO. As shown in Fig. 3, the reduced (Ni0.25Cu0.25)Fe2O4
ꢁ
started to react with CO2 from 400 C and the other reduced ferrites (x ¼ 0.5 and 0.75)
ꢁ
started to react from 500 C. Hence, it is found that oxidizing temperature of the reduced
(NixCu1 –– x)Fe2O4 was increased with increasing Ni content in (NixCu1 –– x)Fe2O4. After the
reaction with CO2, the weight recovering percentages of reduced (NixCu1 –– x)Fe2O4 were
9
0% (x ¼ 0.75), 91% (x ¼ 0.25), and 91.5% (x ¼ 0.5) of the original (NixCu1 –– x)Fe2O4 at
ꢁ
8
00 C. The CO2 decomposition ability
of the reduced (NixCu1 –– x)Fe2O4 showed
the maximum value at x ¼ 0.5.
The off-gas from the CO2 decompo-
sition reaction was analyzed by a quad-
ruple mass spectrometer (Fig. 4). As a
logical product of the CO2 decomposi-
Fig. 2. XRD patterns of (NixCu1 –– x)Fe2O4
ꢁ
reduced up to 800 C by 5% H2 in Ar:
(a) (Ni0.25Cu0.75)Fe2O4,
(b) (Ni0.5Cu0.5)Fe2O4, and
(c) (Ni0.75Cu0.25)Fe2O4

744
H.C. Shin et al.: Carbon Dioxide Decomposition on (NixCu1 –– x)Fe2O4 Solid Solution
Fig. 3. TGA curves of the CO2 de-
composition with reduced
(
(
(
(
NixCu1 –– x)Fe2O4:
a) (Ni0.25Cu0.75)Fe2O4,
b) (Ni0.5Cu0.5)Fe2O4, and
c) (Ni0.75Cu0.25)Fe2O4. Experimental
conditions: 100% CO2, heating rate
ꢁ
1
0 C/min, and flow rate 60 ml/min
tion reaction, CO (m/e ¼ 28) was monitored. It is worthwhile to notice that CO was pro-
duced from CO2 decomposition with the reduced (Ni0.5Cu0.5)Fe2O4 as shown in Fig. 3.
The formation of CO from CO2 gave the important meaning that the carbon deposition
was minimized on the ferrite surface. The carbon formation on the ferrite surface is a
fatal problem for the reversibility of the redox cycle because it covers the ferrite sur-
face and blocks the gas diffusion and inhibits the CO2 decomposition reaction.
The reduced (NixCu1 –– x)Fe2O4 was oxidized by the CO2 decomposition reaction. In
the reaction, the oxidation of reduced (NixCu1 –– x)Fe2O4 generated a mixture of metallic
Ni or Cu and Fe3O4 (Fig. 5). The important point to note is that Ni or Cu was not
ꢁ
oxidized and remained in a metallic state while Fe changed its oxidation state at 800 C
in the presence of CO2. The redox process was summarized as
MFe2O4 ! M þ Fe3O4 $ M þ FeO $ M þ a-Fe,
where M is Cu and Ni.
(3)
Cu and Ni are well known active metallic components in the reduction catalyst. The
incorporation of Cu and Ni in the ferrite structure kinetically facilitated the reduction of
ferrite. The formation of reduced ferrites at lower temperature is strategically important
to mitigate green-house effects by CO2
emission. Moreover, it is valuable to utilize
CO2 as a chemical feedstock. The excellent
reduction behavior of (Ni0.5Cu0.5)Fe2O4
could give us a new opportunity to utilize
CO2 mitigating greenhouse effects.
Fig. 4. Mass signal intensities of CO during CO2
decomposition with reduced (Ni0.5Cu0.5)Fe2O4

phys. stat. sol. (a) 189, No. 3 (2002)
745
Fig. 5. XRD patterns of (NixCu1 –– x)Fe2O4
ꢁ
oxidized up to 800 C by CO2:
(a) (Ni0.25Cu0.75)Fe2O4, (b) (Ni0.5Cu0.5)Fe2O4,
and (c) (Ni0.75Cu0.25)Fe2O4
Summary The redox reaction of (NixCu1 –– x)Fe2O4 solid solution were studied.
(
NixCu1 –– x)Fe2O4 (x ¼ 0.25, 0.5, and 0.75) was prepared for the CO2 decomposition
reaction. The redox reactions of (NixCu1 –– x)Fe2O4 were investigated by thermo-gravi-
metric analysis and X-ray diffraction experiments. (NixCu1 –– x)Fe2O4 showed excellent
reduction reaction with increasing Ni content and excellent CO2 decomposition with
increasing Cu content in (NixCu1 –– x)Fe2O4. The CO2 decomposition ability of the re-
duced (NixCu1 –– x)Fe2O4 showed the maximum value at x ¼ 0.5. CO2 was decomposed
by oxidation of oxygen deficient FeO (FeO1 –– d, 0 ꢀ d ꢀ 1) and the redox reaction was
accelerated by a substituted divalent metal such as Ni and Cu.
Acknowledgements This work was supported by the Interdisciplinary Research
Program of KOSEP, Grant No. 1999-1-301-005-5, and the Ministry of Science and Tech-
nology.
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