Oxidative dehydrogenation of but-1-ene with lattice oxygen in ferrite catalysts

Article abstract of DOI:10.1016/j.apcata.2017.02.004

The oxidative dehydrogenation (ODH) of but-1-ene was carried out using the lattice oxygen in ferrite catalysts in the temperature range of 200–300?°C with a fixed-bed flow reactor at atmospheric pressure. Various ferrite catalysts, such as NiFe₂O₄/AC-500, ZnFe₂O₄/AC-500, CoFe₂O₄/AC-500, and CuFe₂O₄/AC-500, -400, -300, -280, were prepared in the presence of activated carbon in the calcination temperature range of 280–500?°C. When but-1-ene-TPR was measured using various ferrite catalysts, CuFe₂O₄/AC-500 progressed the ODH of but-1-ene at 200–300?°C. Among the catalysts, CuFe₂O₄/AC-500 showed the highest Buta-1,3-diene (BD) yield, at 270?°C. XRD and XPS analyses of the catalyst after the ODH suggested that the lattice oxygen in Cu-O bonded to the tetrahedral site (Cu²⁺_T) of the ferrite structure was used for the ODH. In addition, the used catalyst was recovered by re-oxidation with molecular O₂. Moreover, CuFe₂O₄/AC-280, which calcined at 280?°C, had the highest specific surface area and improved the BD yield with an increase in contact area with but-1-ene. In the repeated ODH (reaction and regeneration cycle), CuFe₂O₄/AC-500 and -280 catalysts maintained BD yields of 7.5% and 11.3%, respectively. BD production is thought to be related to the amount of Cu²⁺_T.

Full text of DOI:10.1016/j.apcata.2017.02.004

Accepted Manuscript
Title: Oxidative dehydrogenation of but-1-ene with lattice
oxygen in ferrite catalysts
Authors: Takayasu Kiyokawa, Naoki Ikenaga
PII:
S0926-860X(17)30049-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2017.02.004
APCATA 16140
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Applied Catalysis A: General
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Accepted date:
12-10-2016
14-12-2016
3-2-2017
Please cite this article as: Takayasu Kiyokawa, Naoki Ikenaga, Oxidative
dehydrogenation of but-1-ene with lattice oxygen in ferrite catalysts, Applied Catalysis
A, General http://dx.doi.org/10.1016/j.apcata.2017.02.004
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Oxidative dehydrogenation of but-1-ene with lattice oxygen in ferrite catalysts
Takayasu Kiyokawa*, Naoki Ikenaga*
Graduate School of Science and Engineering, Kansai University, 3-3-35 Yamate, Suita, Osaka
564-8680, Japan
*Corresponding author: Takayasu Kiyokawa, Naoki Ikenaga
E-mail addresses: k452360@kansai-u.ac.jp (T. Kiyokawa), ikenaga@kansai-u.ac.jp (N. Ikenaga)
Tel.: +81-6-6368-0894
Fax.: +81-6-6388-8869
Key words
Ferrite; But-1-ene; Buta-1,3-diene; Oxidative dehydrogenation, Lattice oxygen
1

Graphical abstract
2

Highlights
1. CuFe2O4/AC catalyst produced BD with oxidative dehydrogenation of but-1-ene at a
lower temperature.
2. The lattice oxygen of Cu-O was used for the ODH and was recovered by molecular
O2.
3. CuFe2O4/AC maintained the BD yield during repeated ODH.
3

Abstract
The oxidative dehydrogenation (ODH) of but-1-ene was carried out using the lattice
oxygen in ferrite catalysts in the temperature range of 200-300 oC with a fixed-bed flow
reactor at atmospheric pressure. Various ferrite catalysts, such as NiFe2O4/AC-500,
ZnFe2O4/AC-500, CoFe2O4/AC-500, and CuFe2O4/AC-500, -400, -300, -280, were
prepared in the presence of activated carbon in the calcination temperature range of
o
280-500 C. When but-1-ene-TPR was measured using various ferrite catalysts,
CuFe2O4/AC-500 progressed the ODH of but-1-ene at 200-300 oC. Among the catalysts,
o
CuFe2O4/AC-500 showed the highest Buta-1,3-diene (BD) yield, at 270 C. XRD and
XPS analyses of the catalyst after the ODH suggested that the lattice oxygen in Cu-O
bonded to the tetrahedral site (Cu2+ T) of the ferrite structure was used for the ODH. In
addition, the used catalyst was recovered by re-oxidation with molecular O2. Moreover,
o
CuFe2O4/AC-280, which calcined at 280 C, had the highest specific surface area and
improved the BD yield with an increase in contact area with but-1-ene. In the repeated
ODH (reaction and regeneration cycle), CuFe2O4/AC-500 and -280 catalysts maintained
BD yields of 7.5% and 11.3%, respectively. BD production is thought to be related to
the amount of Cu2+
.
T
1. Introduction
Buta-1,3-diene (BD) has attracted interest as a monomer of petrochemical products
such as polybutadiene rubber, styrene butadiene rubber, and ABS resin. About 90% of
BD is produced by purifying C4 fraction such as BD, n-butene, and n-butane obtained
from the endothermic steam-cracking of naphtha. However, this process produces many
petrochemicals such as ethylene and propylene at the same time and needs a
4

temperature more than 700 oC. Therefore, this process consumes a lot of energy and can
not produce BD efficiently. However, this process produces many petrochemicals such
as ethylene, propylene at the same time. Therefore, this process consumes a lot of
energy and can not produce BD efficiently.
Recently, oxidative dehydrogenation (ODH) of the C4 fraction with molecular O2
(Eq. (1)) has attracted attention from the perspective of energy saving, because it is an
exothermic process and can more efficiently produce BD at a lower temperature than
the current process. Moreover, since this is single process only to produce BD, BD can
be produced with high selectivity without by-products such as ethylene and propylene.
Moreover, because this process is single process only to produce BD, BD is produced
high selectively without byproducts such as ethylene, propylene.
1-C4H8 (g) + 1/2O2 (g) → C4H6 (g) + H2O (l) H298.15 = -177 kJ/mol
(1)
Various complex metal oxides and supported catalysts have been investigated for the
ODH of many hydrocarbons, such as propane [1], ethylbenzene [2], ethane [3], n-butane
[4], and n-butene [5]. For the ODH of n-butene and n-butane, ferrite-type catalysts
[5-19], V-containing catalysts [20-22], and Bi-Mo catalysts [23-27] exhibited high
activity. It was reported that the Bi-Mo catalyst progressed the ODH through the
Mars−van Krevelen mechanism with oxygen mobility and gave high catalytic activity,
in which the high BD selectivity, low CO2 selectivity, and the high BD yield, for the
ODH of but-1-ene to BD at 440 oC [26]. When the lattice oxygen in the Bi-Mo catalyst
was used for the ODH of but-1-ene, BD and a reduced metal oxide catalyst were
produced, and then the reduced metal oxide was re-oxidized with molecular O2 to
recover the active site in the catalyst [23, 24].
Among these catalysts for the ODH of the C4 fraction, ferrite-type catalysts have
5

been widely studied. Spinel structures, such as Zn-Fe [5-11, 17, 18], Zn-Fe-Cr [13],
Zn-Fe-Al [12], and -Fe2O3 [15, 16], showed high activity. However, the presence of
-Fe2O3 decreased the conversion and the BD selectivity [8]. Among ferrite catalysts,
zinc ferrite has been widely investigated. For example, it was reported that a zinc ferrite
catalyst that was modified by heteropoly acid or sulfonic acid was effective for the
ODH of but-1-ene [9, 10]. In addition, when zinc ferrite was prepared by the
co-precipitation method, pH control was important to obtain high but-1-ene conversion
and high BD selectivity [11].
The reaction mechanism for the ODH of n-butene with the zinc ferrite catalyst is
known to proceed through the Mars−van Krevelen mechanism cycle, the same as that
with the Bi-Mo catalyst [7-9]. However, it was proposed that the ferrite-type catalyst
was deactivated as a result of an increase in Fe2+ produced by reducing Fe3+ that was
isolated from the spinel phase [18, 19]. In order to maintain high oxygen mobility and
inhibit change in the spinel structure, Sb2O4, BiPO4, or SnO2 as an oxygen donor was
added to the zinc ferrite catalyst. These catalysts showed high oxygen mobility and high
ODH activity for a long time [17, 18]. On the other hand, the ODH with the zinc ferrite
catalyst has been carried out under steam and O2 flow. Because the latent heat of steam
o
is large, a high energy level and a high temperature of 400-450 C are necessary.
Furthermore, because the C4 fraction is highly reactive, the complete oxidation reaction
(Eqs. (2), (3)) proceeds easily during the ODH under O2 atmosphere.
1-C4H8 (g) + 6O2 (g) → 4CO2 (g) + 4H2O (l) H298.15 = -2717 kJ/mol (2)
C4H6 (g) + 11/2O2 (g) → 4CO2 (g) + 3H2O (l) H298.15 = -2540 kJ/mol (3)
Therefore, it was proposed that the lattice oxygen of the V-containing SiO2 catalyst
could be used to prevent the complete oxidation of the reactant and the product, and that
6

the catalyst that loses the lattice oxygen can be re-oxidized by introducing molecular O2
after the reaction (Eqs. (4), (5)) [28]. Furthermore, the catalytic activity was maintained
throughout repeated ODHs.
1-C4H8 (g) + MOx (s) → C4H6 (g) + H2O (l) +MOx-1 (s) (4)
MOx-1 (s) +1/2O2 (g) → MOx (s) (5)
It is considered that high oxygen mobility of the lattice oxygen in the catalyst at a lower
reaction temperature would be the most important factor and would show good catalytic
performance for the ODH of the C4 fraction.
Our laboratory, on the other hand, found that ferrite can be prepared at a low temperature,
such as 500 oC, in the presence of activated carbon [29].
This study examined the ODH of but-1-ene with the lattice oxygen in various ferrite
catalysts prepared with activated carbon. In order to inhibit complete oxidation, the lattice
oxygen in the catalyst was used as a mild oxidant, and then the catalytic activity of the ferrite
catalyst for the ODH of but-1-ene was investigated.
2. Experimental
2.1 Materials
.
.
Fe(NO3)3 9H2O (assay
=
min. 99.0%), Ni(NO3)2 6H2O (assay
=
99.0%),
.
.
.
Zn(NO3)2 6H2O (assay = 99.0%), Co(NO3)2 6H2O (assay = 98.0%), Cu(NO3)2 3H2O
(assay = min. 99.0%), and activated carbon (AC) were purchased from Wako Pure
Chemical Industry and were used for the preparation of ferrite catalysts. But-1-ene
(1-C4H8) (assay = min. 99.0%) was supplied from Sumitomo Seika Chemical.
2.2 Catalyst preparation
7

Preparation by impregnation method
Various ferrite catalysts were prepared by the impregnation method. AC was
.
.
impregnated with a mixed aqueous solution of Fe(NO3)3 9H2O and Ni(NO3)2 6H2O,
.
.
.
Zn(NO3)2 6H2O, Co(NO3)2 6H2O, or Cu(NO3)2 3H2O as Ni, Zn, Co, or Cu:Fe=1:2 in
molar ratio. After the mixture was allowed to stand at room temperature overnight,
excess water was evaporated to dryness under reduced pressure. The solid was then
dried at 70 oC overnight in vacuo. Nickel, zinc, and cobalt ferrites were calcined at 500
o
oC for 2 h in air. Copper ferrite was calcined at 280-500 C for 2 h in air. CuO was
o
prepared in same method at 500 C. Hereafter, the notation is NiFe2O4/AC-500,
ZnFe2O4/AC-500, CoFe2O4/AC-500, CuFe2O4/AC-280, -300, -400, -500, and CuO/AC.
2.3 Catalyst test
ODH of but-1-ene using lattice oxygen in ferrite catalyst
The ODH of but-1-ene was carried out using a fixed-bed flow quartz reactor at
various temperatures under atmospheric pressure. After 200 mg of the catalyst was
placed in the reactor, 5 mL/min of but-1-ene and 25 mL/min of Ar were introduced for 8
min. The re-oxidation after ODH was performed under 5 mL/min of O2 and 25 mL/min
of Ar for 8 min at the same temperature as reaction temperature. The relative error of
the experimental operation is within 5 %.
The C4 fractions (1-C4H8, cis-2-C4H8, trans-2- C4H8, and C4H6) were analyzed by a
flame ionization detector (FID) gas chromatograph (Shimadzu GC14B, column:
Unicarbon A-400). CO and CO2 were also analyzed by the FID gas chromatograph
(column: Activated carbon) equipped with a methanizer (Shimadzu MTN-1). H2 was
analyzed by a thermal conductivity detector (TCD) gas chromatograph (Shimadzu
8

GC8A, column: Activated carbon).
2.4 Catalyst characterization
X-ray diffraction (XRD) patterns were obtained by the powder method with a
Shimadzu XRD-6000 diffractometer using monochromatic CuK radiation. X-ray
photoelectron spectra (XPS) analyses were carried out with a JEOL model JPS-9010MX
using MgK radiation as an energy source. The surface area of the catalyst was
measured by the Brunauer–Emmett–Teller (BET) method at 77 K using N2 as an
adsorbate with a MicrotracBEL (BELSORP-mini II-ISP). Thermogravimetry and
differential thermal analysis (TG-DTA) (Shimadzu DTG-60) was used to measure the
burning point of AC. The reactor was heated to 800 oC at a rate of 10 oC /min under 100
o
mL/min of air and was maintained at 800 C for 10 min. A temperature-programmed
reaction of but-1-ene (1-C4H8-TPR) was carried out under but-1-ene/Ar=5/25 mL/min
using a fixed-bed flow reactor in which 200 mg of catalyst was placed. As water
o
removal, the catalyst was pretreated at 200 C under an Ar atmosphere, and then the
o
o
reactor was heated to 500 C at a rate of 5 C/min under but-1-ene and Ar flow. The
products (H2, H2O, C4H6, CO2) were continuously analyzed by a Q-mass mass
spectrometer (Hiden Analytical, HAL 201) fitted with an outlet of the reactor.
3. Results and Discussion
3.1 Activity test of various ferrite catalysts by 1-C4H8-TPR measurement
1-C4H8-TPR was measured in order to confirm the lattice oxygen mobility of ferrite
catalysts such as NiFe2O4/AC-500, ZnFe2O4/AC-500, CoFe2O4/AC-500, and
CuFe2O4/AC-500. The results are shown in Fig. 1. Since H2O and CO2 were seen at 380
9

o
oC, NiFe2O4/AC-500 progressed the complete oxidation of but-1-ene. At about 400 C,
NiFe2O4/AC-500 progressed the decomposition of but-1-ene to produce H2. The
o
formation of CO2 increased from about 460 C. However, the production of H2O was
not seen. Therefore, carbon produced by the decomposition of but-1-ene seemed to be
oxidized by the lattice oxygen (Fig. 1 a)). On the other hand, CoFe2O4/AC-500 and
ZnFe2O4/AC-500 produced BD, although the latter produced BD and H2 at over 400 oC.
Since H2O was not observed, this catalyst progressed the simple dehydrogenation of
but-1-ene (Fig. 1 b)). CoFe2O4/AC-500 catalyst produced BD, H2O, CO2, and H2 at over
o
400 C. Therefore, this catalyst proceeded to the ODH, the complete oxidation, and the
simple dehydrogenation of but-1-ene at the same time (Fig. 1 c)). When
CuFe2O4/AC-500 was used to measure 1-C4H8-TPR, BD and H2O were produced at
over about 200 oC (Fig. 1 d)). At 300 oC, CO2 and H2O were formed with the complete
oxidation of but-1-ene. Since H2 formed at over 400 oC, the decomposition of but-1-ene
progressed. These results indicate that CuFe2O4/AC-500 catalyst is the most suitable for
ODH at a lower temperature. Since CuFe2O4/AC-500 produced CO2 at 300 oC and H2 at
o
400 C, the ODH using CuFe2O4/AC-500 was carried out at a temperature range of
200-300 oC.
3.2 Effect of reaction temperature on ODH with lattice oxygen of CuFe2O4/AC-500
The ODHs with lattice oxygen of CuFe2O4/AC-500 were carried out at 200-300 oC.
o
The results are illustrated in Fig. 2. When the ODH was conducted at 200 C,
CuFe2O4/AC-500 indicated the highest conversion, of 25.6%, with the isomerization
reaction. However, low BD selectivity of 17.9% and low BD yield of 4.6% were
o
obtained. In the ODHs at 250-270 C, this catalyst exhibited higher conversion, BD
10

o
selectivity, and BD yield. At 270 C, CuFe2O4/AC-500 gave a conversion of 21.3%,
o
high BD selectivity of 39.9%, and the highest BD yield, 8.5%. At 300 C, this catalyst
showed low conversion of 12.8% as the isomerization reaction declined, high CO2
selectivity of 14.2%, and a low yield of 6.5%. Since the catalyst gave the highest BD
o
o
yield at 270 C, 270 C was the most suitable reaction temperature for the ODH with
CuFe2O4/AC-500.
XRD analyses were carried out to examine the change in the crystallite structure of
the catalyst before and after the ODH and after the re-oxidation at 270 oC. XRD patterns
are shown in Fig. 3. CuFe2O4 and CuO diffraction peaks were seen in CuFe2O4/AC-500
before the ODH (Fig. 3a)). CuFe2O4/AC-500 after the reaction exhibited diffraction
peaks of metal copper in addition to copper ferrite, and CuO diffraction peak was
clearly decreased as compared to that of the fresh catalyst (Fig. 3b)). The lattice oxygen
in CuO may also be used for the ODH of but-1-ene. In order to confirm the reactivity of
the lattice oxygen, CuO/AC catalyst was used for the ODH of but-1-ene. When the
CuO/AC was used for the ODH, CuO indicated the lower conversion of 1.9 %, the
higher CO2 selectivity of 36.9 %, and the lower BD yield of 0.9 % than those of
CuFe2O4/AC catalyst. In other words, the reducibility of the lattice oxygen in CuO is
very low. Therefore, it is suggested that the lattice oxygen in CuFe2O4 is more effective
than that of CuO for the ODH. After the re-oxidation, CuFe2O4 and CuO diffraction
peaks were similar to those of the catalyst before the reaction. Furthermore, since the
crystallite sizes of CuFe2O4 in CuFe2O4/AC-500 before and after the reaction calculated
by the Scherrer equation were 8.8 nm and 10.4 nm, respectively (Fig. 3c)), the CuFe2O4
crystallite barely grew. Therefore, the crystal structure in the used CuFe2O4/AC-500
could be recovered by re-oxidation.
11

To investigate the active species for the ODH with CuFe2O4/AC-500 and the change
in valence values of iron and copper oxide species, XPS analyses were used for
o
CuFe2O4/AC-500 before and after the reaction at 270 C. XPS spectra of Fe and Cu
species are shown in Fig. 4. In general, the XPS spectra of Fe and Cu species of CuFe2O4
can be divided into two peaks, such as octahedral and tetrahedral sites [30, 31]. Fe3+ species
related to tetrahedral (Fe3+ ) and octahedral (Fe3+O) sites appear at 713.6 and 710.5 eV,
T
respectively. Cu2+ species related to tetrahedral (Cu2+ ) and octahedral (Cu2+O) sites appear at
T
935.8 and 934.1 eV, respectively. XPS spectra of CuFe2O4/AC-500 before the reaction
indicated Fe3+ and Cu2+ were related to tetrahedral and octahedral sites, respectively (Fig. 4 a),
b)). According to the XPS analysis of CuFe2O4/AC-500 after the ODH, because XPS spectra
of reduced Fe species were not observed in the catalyst after the reaction, lattice oxygen in the
Fe-O bond was not used for the ODH (Fig. 4 a)).
On the other hand, Cu0 appeared at 932.1 eV in addition to two peaks with Cu2+ related to
tetrahedral and octahedral sites in the catalyst after the reaction (Fig. 4 b)). Moreover, Cu2+T in
CuFe2O4/AC-500 catalyst clearly decreased after the ODH. XPS spectrum of
CuFe2O4/AC-500 after the re-oxidation showed Cu2+T in addition to Cu2+O, similar to those
of the catalyst before the reaction. Therefore, oxygen species bonded to Cu2+ would be
T
used as active sites for the ODH of but-1-ene. Iron oxide species did not relate to the ODH.
However, it is thought that the iron species is necessary to form Cu2+T by combining Fe
and Cu. The ODH of but-1-ene to BD was promoted by forming Cu2+ . The atomic ratio of
T
Cu and O on CuFe2O4/AC-500 surface before and after the reaction and after the
re-oxidation calculated from XPS analyses are shown in Table 1. Although Cu species/O
atomic ratio (b)) on the catalyst surface after the ODH was increased from 0.37 to 0.46
as compared to that (a)) of fresh catalyst. For the catalyst after the re-oxidation, Cu
12

species/O ratio was decreased from 0.46 to 0.4 as compared to that of the catalyst after
the ODH. As indicated in Fig. 4, the change in the valence value of Fe species was not
seen. Therefore, the lattice oxygen on only copper oxide species can be used for the
ODH of but-1-ene, and the used lattice oxygen can be regenerated by the re-oxidation.
According to the results of XRD and XPS analyses, because the used CuFe2O4/AC-500
catalyst could be regenerated by re-oxidation with oxygen, the re-oxidized CuFe2O4/AC-500
can be used for the ODH of but-1-ene again.
3.3 Effect of calcination temperature on ODH
The effects of the specific surface area and the crystallite size of CuFe2O4 in
CuFe2O4/AC-500 catalyst with a change in the calcination temperature on the ODH were
examined.
In order to confirm the burning point of AC, TG-DTA measurement of CuFe2O4/AC
before calcination was carried out. The results are illustrated in Fig. 5. Remarkable weight
loss and increased DTA were observed at 300 oC with burning AC. Therefore, CuFe2O4/AC
catalysts were calcined at 280-500 oC. Their XRD patterns are shown in Fig. 6, and the
specific surface area and crystallite size are shown in Table 2. CuFe2O4 diffraction peaks
were observed for all catalysts (Fig. 6 a)-d)). Therefore, it is considered that the crystal
structure of CuFe2O4 would be formed by AC burning, because no DTA increase or weight
gain, which are related to the formation of iron and copper oxide after AC burning, was seen
(Fig. 5). On the other hand, the specific surface area increased in the order of
CuFe2O4/AC-280>300>400>500=105>76>59>34 m2/g and the crystallite size tended to
decrease in the order of CuFe2O4/AC-280<300<400<500=6.8<7.4<8.1<8.8 nm as the
o
calcination temperature decreased (Table 2). When the catalyst was calcined at 280 C,
13

it showed a higher specific surface area of 105 m2/g and a smaller crystallite size of 6.8
nm compared to those of catalysts calcined at other temperatures.
The effects of the calcination temperature on the ODH are shown in Fig. 7.
CuFe2O4/AC-400 and CuFe2O4/AC-500 gave quite similar BD yields of about 8.5%.
CuFe2O4/AC-300 showed a higher conversion, 24.4%, and a higher BD yield, 8.8%.
When the ODH was carried out using CuFe2O4/AC-280, conversion of 27.6% and a BD
yield of 9.2% were obtained. CuFe2O4/AC, which has a high specific surface area,
tended to give a high BD yield because of the larger contact area with but-1-ene.
3.4 Evaluation of activity maintenance for repeated ODH
ODHs and re-oxidation were repeated using CuFe2O4/AC-500 and
CuFe2O4/AC-280. The results are shown in Figs. 8 and 9, respectively. For
CuFe2O4/AC-500 (Fig. 8), the second reaction gave a lower conversion, 8.8% and a
lower BD yield, 4.7%, and higher CO2 selectivity, 11.3%, than those of the first reaction.
The increase in the CO2 selectivity after the second ODH indicated that the complete
oxidation of C4 fraction such as but-1-ene and BD progressed. Thereafter, the
conversion and the BD selectivity gradually increased from third to eighth ODH. After
the seventh ODH, lower conversion of 15%, BD yield of 7.5%, higher BD selectivity of
48.2%, and CO2 selectivity of 4.2% were maintained. The BD yield stabilized at the
eighth ODH, and CuFe2O4/AC-500 stably produced BD in the repeated ODH. When
CuFe2O4/AC-280 was used for the repeated ODH (Fig. 9), in the second ODH, the
conversion decreased from 26.9% to 17%, similar to that of CuFe2O4/AC-500. Even at
the tenth ODH, the conversion increased from 26.9% to 32.6% with the isomerization
reaction, BD selectivity of about 35% was maintained, and CO2 selectivity decreased
14

relative to that at the second ODH. The BD yield then increased from 9.3% to 11.3%.
To examine the change in the crystal structure during the repeated ODHs, XRD
analyses of CuFe2O4/AC-500 and -280 were carried out after the repeated ODHs. The
XRD patterns are shown in Fig. 10.
CuO diffraction peaks in both catalysts after the repeated ODHs were larger than
those before the reaction (Fig. 10 a), b)). However, as already mentioned in section 3.2,
since CuO/AC showed the lower conversion, the high CO2 selectivity, and the low BD
yield, the results after the second ODH (Figs. 8, 9) show that CuFe2O4 produced by
liberated Cu species from the spinel phase inhibited the complete oxidation of but-1-ene
and encouraged the isomerization reaction.
In order to evaluate the effects of Cu species such as tetrahedral and octahedral sites
on the repeated ODHs, XPS analyses were used for the CuFe2O4/AC-500 and -280 after
the repeated ODHs. The ratios of Cu2+T/Cu2+O calculated from XPS analyses are shown
in Table 3. The ratio of Cu2+T/ Cu2+O of CuFe2O4/AC-500 after the first ODH was lower
than that of the fresh catalyst (Table 3 a), b)), but the Cu2+T/ Cu2+O ratio after the eighth
ODH was higher than that after the first re-oxidation (Table 3 b), c)). Therefore, the BD
yield gradually recovered and stabilized at the eighth ODH. The Cu2+T/ Cu2+ ratio in
O
CuFe2O4/AC-280 after the first re-oxidation was lower than that of the fresh catalyst
(Table 3 d), e)). However, the Cu2+T/ Cu2+ ratio after the tenth ODH increased from
O
0.26 to 0.36 compared to the fresh catalyst (Table 3 d), f)). These results suggested that
an increase in the BD yield is related to the amount of Cu2+T phase. Therefore, although
the role of Cu2+T phase is not clear, its existence might be the most important factor for
BD production in the ODH of but-1-ene.
15

4. Conclusion
o
CuFe2O4/AC-500 gave a BD yield of 8.5% at 270 C, and the used catalyst was
regenerated by re-oxidation with molecular O2. The results of XRD and XPS analyses
of CuFe2O4/AC-500 after the ODH showed that the ODH progressed by using the
lattice oxygen of Cu-O bonded in Cu2+T. The CuFe2O4/AC catalyst that had a higher
specific surface area was more efficient for the ODH, and CuFe2O4/AC-280, which had
the highest specific surface area, 105 m2/g, gave the highest BD yield, 9.3%.
For the repeated ODHs using CuFe2O4/AC-500 and CuFe2O4/AC-280,
CuFe2O4/AC-500 maintained a BD yield of about 8% until the eighth ODH. When
CuFe2O4/AC-280 was used for the repeated ODHs, BD was formed until the tenth ODH
and the BD yield increased from 9.5% to 11.3%. From the XRD and XPS analyses of
CuFe2O4/AC-500 and CuFe2O4/AC-280 after the repeated ODHs, the generation of
CuO is involved in the inhibition of complete oxidation of but-1-ene. In addition, the
increase in Cu2+T phase seemed to increase the BD yield in the ODH of but-1-en.
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18

6. Acknowledgment
This research was financially supported in part by the Kansai University Grant-in-Aid
for progress of research in graduate course, 2016
19

Justification for Publication
This manuscript exceeds the default character count described in the author guidelines, but this
original manuscript contains very significant results and discussions required to clarify the specific
and excellent effects of the design of an attractive ferrite catalyst that can produce BD at a lower
reaction temperature than was used in other studies on the ODH of but-1-ene.
20

Table 1 Cu and O atomic ratio of CuFe2O4/AC-500 catalyst before
and after ODH and after re-oxidation calculated from XPS analysis
Fresh, used, and re-oxidized
catalysts
Cu2+,
0/O
a) CuFe2O4/AC-500 fresh
0.37
b) CuFe2O4/AC-500 after ODH
0.46
CuFe2O4/AC-500 after
re-oxidation
c)
0.40
21

Table 2 Specific surface area and crystallite size of CuFe2O4/AC
catalyst prepared at different calcination temperatures
Specific surface area
Sample
Crystallite size (nm)
(m2/g)
34
CuFe2O4/AC-500
CuFe2O4/AC-400
CuFe2O4/AC-300
CuFe2O4/AC-280
8.8
8.1
7.4
6.8
59
76
105
22

Table 3 Cu2+ /Cu2+ ratio of CuFe2O4/AC catalyst before and after
T
O
ODH calculated from XPS analysis
Fresh and used catalyst
Cu2+ Cu2+
T
O
Cu2+ /Cu2+
T
O
(%)
(%)
a)
b)
c)
d)
e)
f)
CuFe2O4/AC-500 fresh
20.5 79.5
17.9 82.1
20.2 79.8
20.8 79.2
18.4 81.6
26.7 73.3
0.26
0.22
0.25
0.26
0.23
0.36
CuFe2O4/AC-500 after first re-oxidation
CuFe2O4/AC-500 after eighth ODH
CuFe2O4/AC-280 fresh
CuFe2O4/AC-280 after first re-oxidation
CuFe2O4/AC-280 after tenth ODH
23

H2
H2O
BD
a)
b)
NiFe2O4/AC-500
CO2
H2
ZnFe2O4/AC-500
H2O
BD
CO2
c) CoFe2O4/AC-500
H2
H2O
BD
CO2
d)
CuFe2O4/AC-500
H2
H2O
BD
CO2
100
200
300
500
400
Temperature / oC
Fig.1 But-1-ene-TPR profiles with various ferrite catalysts
Catalyst weight: 200 mg, 1-C4H8=/Ar=25/5 mL/min, heating ratio: 5 oC/min,
a) NiFe2O4/AC-500, b) ZnFe2O4/AC-500, c) CoFe2O4/AC-500, d) CuFe2O4/AC-500

30
25
20
15
10
5
20
15
10
5
0
0
200
220
240
260
280
300
Reaction temperature /oC
100
80
60
40
20
0
Selectivity /%
BD
cis-2-C4H8
trans-2-C4H8
CO
CO2
200
250
260
270
300
Reaction temperature /oC
Fig. 2 Oxidative dehydrogenation of but-1-ene with copper ferrite catalyst
Catalyst: CuFe2O4/AC-500, catalyst weight: 200 mg,
flow rate: 1-C4H8/Ar=5/25 mL/min, reaction time: 8 min

（3 1 1）
CuFe2O4
CuO
Cu
CuFe2O4/AC-500
Fresh
a)
8.8 nm
CuFe2O4/AC-500
After the ODH
b)
c)
CuFe2O4/AC-500
After re-oxidation
10.4 nm
10
20
30
40
50
60
70
80
2θ /Degree
Fig. 3 XRD patterns of copper ferrite after ODH and re-oxidation
a) CuFe2O4/AC-500 before reaction, b) CuFe2O4/AC-500 after the ODH at 270 oC,
c) CuFe2O4/AC-500 after re-oxidation at 270 oC

Cu(2p3/2)
b)
934.1 eV
Cu2+O：934.1 eV
Cu2+ ：935.8 eV
T
Fe(2p3/2)
Cu0: 932.4 eV
Fe3+O：710.5 eV
a)
935.8 eV
Fe3+ ：713.6 eV
T
932.4 eV
CuFe2O4/AC-500
Fresh
713.6 eV
710.5 eV
CuFe2O4/AC-500
Fresh
CuFe2O4/AC-500
After the ODH
CuFe2O4/AC-500
After the ODH
CuFe2O4/AC-500
After re-oxidation
725
710
940 938 936 934 932 930 928 926
Binding energy / eV
705
715
720
Binding energy / eV
Fig. 4 XPS spectra of CuFe2O4/AC before and after the ODH and re-oxidation
a) Cu(2p3/2) before and after the ODH and re-oxidation at 270 oC, b) Fe (2p3/2)
before and after the ODH at 270 oC

100
80
1000
800
600
400
200
0
DTA
1000
800
600
400
200
0
60
Temperature
40
0
20
40
Time / min
60
80
Fig. 5 Weight loss and DTA of copper ferrite before calcination by TG-DTA
Substance: CuFe2O4/AC before calcination, flow rate: air=100 mL/min,
heating ratio: 5 oC/min

500 oC
a)
CuFe2O4
CuO
400 oC
b)
300 oC
280 oC
c)
d)
10
20
30
40
50
60
70
80
2θ /Degree
Fig. 6 XRD patterns of copper ferrite calcined at various temperatures
Calcination temp: a) 500 oC, b) 400 oC, c) 300 oC, d) 280
Catalyst notice: a) CuFe2O4/AC-500, b) CuFe2O4/AC-400, c) CuFe2O4/AC-300,
d) CuFe2O4/AC-280