Hydrogen and carbon nanotubes production by catalytic of ethanol over the Co-Mo catalysts

Article abstract of DOI:10.1166/jnn.2018.15227

A series of Cobalt-Carbon, Cobalt-Molybdenum-Carbon catalysts were prepared by impregnation. The molar ratios of Co:Mo were 9:1, 8:2 and 7:3 and the total metal weights of them in the supported catalysts were 5 wt%. Moreover, the effects of reaction temperature and the Co:Mo molar ratios on the produce hydrogen and carbon nanotubes were investigated systematically. Of all the catalysts, Co-Mo (5 wt%, Co:Mo = 9:1)/C was the most effective one on the basis of hydrogen yield (84%), ethanol conversion (95%) and the quality of carbon nanotubes at 600 °C. A small amount of Mo added into the Co/C catalysts resulted in increasing in the yield of hydrogen and improving on quality of carbon nanotubes from ethanol decomposition over the Co-Mo catalysts.

Full text of DOI:10.1166/jnn.2018.15227

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 4387–4392, 2018
Copyright © 2018 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Hydrogen and Carbon Nanotubes Production by
Catalytic of Ethanol Over the Co–Mo Catalysts
1ꢀ2
3
1
1ꢀ∗
Jinxiang Diao , Gang Wang , Xiaojie Liu , and Hui Wang
1Key Laboratory of Synthetic and Natural Functional Molecule Chemistry (Ministry of Education),
College of Chemistry and Materials Science, Northwest University, Xi’an, 710069, P. R. China
2
Aeronautical Polytechnic Institute, Xi’an, 710089, P. R. China
3
National Key Laboratory of Photoelectric Technology and Functional Material,
Institute of Photonics and Photon-Technology, Northwest University, Xi’an, 710069, P. R. China
A series of Cobalt–Carbon, Cobalt–Molybdenum–Carbon catalysts were prepared by impregnation.
The molar ratios of Co:Mo were 9:1, 8:2 and 7:3 and the total metal weights of them in the supported
catalysts were 5 wt%. Moreover, the effects of reaction temperature and the Co:Mo molar ratios on
the produce hydrogen and carbon nanotubes were investigated systematically. Of all the catalysts,
Co–Mo (5 wt%, Co:Mo = 9:1)/C was the most effective one on the basis of hydrogen yield (84%),
ꢀ
ethanol conversion (95%) and the quality of carbon nanotubes at 600 C. A small amount of Mo
added into the Co/C catalysts resulted in increasing in the yield of hydrogen and improving on
quality of carbon nanotubes from ethanol decomposition over the Co–Mo catalysts.
IP: 188.72.126.53 On: Mon, 17 Sep 2018 06:44:41
Keywords: Carbon Nanotubes, Co–Mo/C Catalyst, Hydrogen, Chemical Vapor Deposition,
Copyright: American Scientific Publishers
Ethanol Decomposition.
Delivered by Ingenta
1
. INTRODUCTION
industry.23 There exist four traditional methods of hydro-
gen production: Water electrolysis, gasification reaction,
Carbon nanotubes (CNTs) have been paid increasing
attention due to their extraordinary mechanical, electri-
cal and thermal properties, since discovered by Iijima.
partial oxidation reaction of heavy oil and hydrocar-
1
2
24–27
bon steam reforming reaction.
The method of hydro-
The potential applications of CNTs in areas such as car-
bon nanotubes composite materials, catalyst support and
gen production by the ethanol reforming attracted great
interest in the application, which is due to the char-
acteristics of renewable source, relativity high hydrogen
content, non-toxicity, safe storage, handing and realiz-
3
–8
hydrogen storage have been reported. In order to fulfill
the potential application, large-scale production of CNTs
was crucial. Recently, many methods have been devel-
2
8ꢀ29
ing in large industrial.
Many groups reported that
9
oped for CNTs preparation, such as arc discharge, laser
hydrogen production over the Co-based catalysts and
1
0
11ꢀ12
30–32
vaporization, and chemical vapor deposition (CVD).
MoC
2
/C for ethanol steaming reforming.
In addition,
Among these methods, CVD shows best advantages of
low cost and mass production of CNTs. The most used
catalysts for CVD technique are transition metals Co,
Fe, Ni or their alloy and as co-catalysts Mo, Cr, Ru,
our group has recently reported that co-production hydro-
gen and CNTs by ethanol decomposition over the Co/C
catalysts. In order to improve the active of Co-based
catalysts performance, massive Co catalysts doped with
different Mo loadings were prepared using C as the
support.
3
3
1
3–16
Pt.
Co–Mo catalysts are very effective for single-wall
1
7–19
carbon nanotubes
and multi-wall carbon nanotubes
Fewer studies have dealt with the pro-
2
0–22
(
MWCNTs).
In the present work, the co-production of H and CNTs
2
duction of hydrogen and CNTs over Co–Mo catalysts from
ethanol decomposition.
Hydrogen, recently recognized as an important raw
material and energy carrier, is widely used in the
from ethanol decomposition over C-supported Co–Mo cat-
alysts was investigated systematically in the range of tem-
perature of 500–700 C. The effects of the temperature
ꢀ
and the molar ratio of Co:Mo on the performance of
Co–Mo/C catalysts in co-producing H and CNTs by cat-
alytic decomposition of ethanol was discussed in detail.
2
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 6
1533-4880/2018/18/4387/006
doi:10.1166/jnn.2018.15227
4387

Hydrogen and Carbon Nanotubes Production by Catalytic of Ethanol Over the Co–Mo Catalysts
Diao et al.
3
4
The optimal growth conditions of CNTs were presented.
The role of molybdenum in Co–Mo/C for the production
of CNTs and hydrogen was proposed.
various gas products (S ꢁ, which were defined as
follows:
i
H yield ꢃ%ꢁ
2
mole of H atom converted to H2
2
. EXPERIMENTAL DETAILS
=
theoretical mole of H atomcontained in ethanol feed
Co–Mo catalysts supported on graphite with different
molar ratio of Co:Mo were prepared by impregnation as
described as follow. Co (NO ꢁ ·6H O and (NH ꢁ Mo O ·
×
100
(1)
Ethanol conversion ꢃ%ꢁ
3
2
2
4
6
7
24
4
H O was dissolved in distilled water, and then 3 g C
2
mol (ethanol) in−mol (ethanol) out
was added into the aqueous solution. The reaction was
further stirred at room temperature for 8 h to achieve a
homogeneous impregnation of salts in support. The homo-
=
×100 (2)
mol (ethanol) in
ni
Si =
×100
(3)
ntotal
ꢀ
geneous mixture was dried in oven at 80 C for 12 h and
the material was grounded in mortar to break the chunks
into fine powder. The prepared of catalysts were denoted
as Co–Mo (Co:Mo = X)/C, total metal amount was 5 wt%
Where n is the molar of i gas product (i = H , CO, CH
i
2
4
or CO ꢁ, and n
the total molar of all the gas products
2
total
4
(
H +CO+CH +CO ꢁ.
2
2
(
(Co+Mo)/(Mo+Co+C)= 5 wt%) in the supported cat-
alyst and the molar ratio of Co:Mo in the catalysts was
adjusted to be 9:1, 8:2 and 7:3. The experimental was car-
ried out in a conventional gas flow system with a vertical
fixed bed at the center of a quartz tubular reactor (inner
diameter 5 mm) as the reaction chamber. The tempera-
ture of the bed was monitored with a thermocouple touch-
ing the outside wall of the reactor in close proximity to
the sample bed. Prior to ethanol decomposition, the cat-
3
. RESULTS AND DISCUSSION
Figure 1 showed the effects of reaction temperature and the
molar ratio of Co:Mo on the H yield in the ethanol decom-
2
position over the Co–Mo/C catalysts at the temperature of
ꢀ
ꢀ
ꢀ
5
00 C, 600 C and 700 C. Figures 1(a)–(c) showed the
changes of H yield as a function of reaction time. It was
2
significant from Figure 1(a) that the H yield reduced as the
2
ꢀ
ꢀ
molar ratios of Co:Mo decreases from 9:1 to 7:3 at 500 C.
alyst (150 mg) was reduced by hydrogen at 500 C for
The H yield reduced from 78% to 68%. From Figure 1(b),
1
h and subsequently purged under Ar at the same tem-
2
IP: 188.72.126.53 On: Mon, 17 Sep 2018 06:44:41
ꢀ
the average H yield at 600 C for Co:Mo ratio of 9:1, 8:2,
yield
was 50% over the Co (5 wt%)/C at 600 C within 60 min.
perature for 40 min. Then the deco mC p oo ps iy t ri oi gn h to: fA emt h ea rni co al n Scientific Publi
was performed on Co–Mo/C at the temperatur eD oe fl iv 5e0 r 0e ,d bya Inn dg 7e :n3 t aw as calculated to be 84%, 73% and 63%. H
6
jector into a vaporizing chamber (100 C) at a flow rate
of 0.3 ml/h and switched to the tubular reactor using Ar
2
shers
2
ꢀ
ꢀ
00 and 700 C. Ethanol was injected through a microin-
ꢀ
The increment of the average of H
yield was 32%. At
2
ꢀ
700 C, the change of H
yield was not various and the H
2
2
(
40 ml/min) as the carrier gas. During ethanol decompo-
yield was 55% in Figure 1(c). It was determined that the
ꢀ
sition, the gaseous products in the exit gases from the
tubular reactor were analyzed at 12 min intervals by a
gas chromatography (GC). After 60 min, the injection of
ethanol was stopped and the solid products were collected
from the tubular reactor. The gas products were analyzed
using on-line gas chromatograph (SP-9890, SP-6890). The
morphologies of the CNTs were characterized by the scan-
ning electron microscopy (SEM) performed on FEI Quanta
optimal reaction temperature was 600 C and that the opti-
mal molar ratio of Co:Mo was 9:1 for H
decomposition over Co–Mo/C catalysts. For this situation,
the H yield was 84%. It could be concluded that molybde-
yield from ethanol
2
2
num addition in small amount (Co:Mo = 9:1) to the Co/C
catalyst increased H
600 C. It was reported that the H
yield at relatively high temperature of
yield of 52% through
2
ꢀ
2
auto-thermal reforming of bio-ethanol over Co-based cata-
ꢀ
35
4
00 ESEM-FEG, Raman scattering studies of the CNTs
lysts at 600 C. Our experimental result indicated that H2
were performed at room temperature using a dispersive
Raman spectrometer (Nicolet, ALMEGA) with the exci-
tation wavelength of 523 nm. Composition analyses of
solid products were carried out by X-ray diffraction (XRD,
D/max-3c, Cu Kꢂ, 50 kV, 300 mA, at the room tempera-
ture in air). The quality and microstructures of the CNTs
were investigated with transmission electron microscopy
yield for the Co–Mo (5 wt%, Co:Mo = 9:1)/C catalyst at
ꢀ
600 C reached 84%, which was much higher than reported.
Figure 2 showed the effects of reaction temperature on
gas selectivity within 60 min. In addition to hydrogen in
gas products, as shown in Figures 2(a)–(d), carbon monox-
ide, methane and carbon dioxide are also detected from
ethanol decomposition over Co (5 wt%)/C and Co–Mo
(
TEM) performed on a JEOL JEM-3010 high-resolution
(Co:Mo = X)/C catalysts in the temperature range of 500–
ꢀ
transmission electron microscopy (HRTEM) at an acceler-
ating voltage of 300 kV.
700 C, with their selectivities (S ꢁ changing in the order
i
of H > CO > CH > CO . Figure 2(a) showed that the
2
4
2
The catalytic behaviors of the Co–Mo/C cata-
lysts for ethanol decomposition were evaluated by
H2 yield, ethanol conversion and the selectivity of
H selectivity over the Co–Mo/C on the basis of reaction
2
ꢀ
temperature. At 500 C, H selectivity was higher over
2
the Co (5 wt%)/C than Co–Mo/C. Hydrogen selectivity
4388
J. Nanosci. Nanotechnol. 18, 4387–4392, 2018

Diao et al.
Hydrogen and Carbon Nanotubes Production by Catalytic of Ethanol Over the Co–Mo Catalysts
Co/C
Co:Mo=8:2
Co:Mo=7:3
Co/C
Co:Mo =8:2
Co:Mo =7:3
Co:Mo=9:1
Co:Mo =9:1
(a) 100
(a) 100
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
500ºC
(
b) 30
(b)
2
2
1
1
5
0
5
0
5
0
5
8
6
4
2
0
0
0
0
(
c)
6
00ºC
(c)
0
0
0
0
0
0
1
IP: 188.72.126.53 On: Mon, 17 Sep 2018 06:44:41
1
0
8
6
4
2
Copyright: American Scientific Publishers
Delivered by Ingenta
5
0
3
2
.5
3
(d)
700ºC
.5
2
0
10
20
30
40
50
60
Reaction time / min
Figure 1. Change of H2 yield as a function of the reaction time in
ethanol decomposition over Co/C (5 wt%)/C and Co–Mo/C with different
1.5
1
moral ratio of Co:Mo 9:1, 8:2 and 7:3 at different temperature: (a) 500,
ꢀ
(
b) 600 and (c) 700 C.
0.5
reached highest on the Co–Mo (Co:Mo = 9:1)/C (80%) at
ꢀ
6
00 C and the change of hydrogen selectivity was not
0
500
600
700
ꢀ
obvious at 700 C. Meanwhile, Figure 2(b) CO selectivity
Reaction temperature /ºC
was least on the Co–Mo (Co:Mo = 9:1) (14%). The addi-
Figure 2. Change of selectivity of gas products as a function of the
reaction temperature in ethanol decomposition over Co (5 wt%)/C and
Co–Mo/C with different moral ratio of Co:Mo (9:1, 8:2 and 7:3) at dif-
tion of Mo to the Co/C catalyst made the CH increased
4
ꢀ
obviously at higher temperature (700 C) (in Fig. 2(c)).
The CO selectivity did not change significantly with the
ꢀ
2
ferent temperature: 500, 600 and 700 C.
temperature and the ratio of Co:Mo varying. Figure 3
showed the effect of reaction temperature on ethanol con-
version from the ethanol decomposition over the Co–Mo/C
catalysts. With the ratio of Co:Mo rising from 7:3 to 9:1,
ꢀ
ꢀ
increased and then decreased at 600 C and 700 C.
When the ratio of Co:Mo was 9:1, ethanol decomposition
highest (95%), which was corresponding with the
ꢀ
ethanol conversion was decreased at 500 C and firstly
H yield.
2
J. Nanosci. Nanotechnol. 18, 4387–4392, 2018
4389

Hydrogen and Carbon Nanotubes Production by Catalytic of Ethanol Over the Co–Mo Catalysts
Diao et al.
Co/C
Co:Mo = 8:2
Co:Mo = 7:3
Graphite
Co O
Co:Mo = 9:1
3
4
1
00
MoO
3
8
6
4
2
0
0
0
0
0
2
0
30
40
50
60
70
2
thetal/degree
Figure 5. XRD pattern of MWCNTs formed by ethanol decomposition
over Co–Mo (Co:Mo = 1:9)/C catalyst at 600 C.
5
00
600
700
ꢀ
Figure 3. Ethanol conversion over Co (5 wt%)/C and Co–Mo/C cata-
lysts with different moral ratio of Co:Mo 9:1, 8:2 and 7:3 at 500, 600
and 700 C within 60 min.
ꢀ
at 600 C. Figure 4(c) showed carbon nanofibers (CNFs)
ꢀ
ꢀ
with width diameter are formed at 700 C, accompanied
with the sintering of catalysts. It presented that the Co–Mo
ꢀ
Solid products deposited on the Co–Mo/C catalysts were
characterized by SEM. Figures 4(a)–(c) presented that the
SEM images of CNTs over Co–Mo (Co:Mo = 9:1)/C at
(Co:Mo = 9:1)/C catalyst at temperature of 600 C was
ꢀ
more effective than that at temperatures of 500 and 700 C,
in terms of CNTs production from ethanol decomposition.
The reason was that Mo is considered as a role in dispers-
ꢀ ꢀ ꢀ
00 C, 600 C and 700 C, and the temperature was
5
ꢀ
essential to produce CNTs. The SEM images indicated that
CNTs were formed rarely at 500 C. However, Figure 4(b)
showed the length of CNTs with few metals and a little
amorphous carbon formed over Co–Mo (Co:Mo = 9:1)/C
ing metallic Co at temperature of 600 C. The Co–Mo/C
ꢀ
IP: 188.72.126.53 On: Mon, 17 Sep 2018 06:44:41
catalysts were sintered and reunited at relatively higher
temperature of 700 C, which leads to larger Co metal par-
ticles. The larger metal particles favored the carbon fiber
Copyright: American Scientific Publishers
ꢀ
Delivered by Ingenta
(a) Co:Mo=9:1, 500 ºC
(b) Co:Mo=9:1,ꢀ600 ºC
(c) Co:Mo=9:1,ꢀ700 ºC
(d) Co( 5wt%)/C, 600 ºC
(e) Co:Mo=8:2, 600 ºC
(f) Co:Mo=7:3, 600 ºC
Figure 4. SEM images of MWCNTs formed by the ethanol over the Co–Mo (Co:Mo = 9:1)/C catalysts at different temperatures: (a) 500, (b) 600
ꢀ
ꢀ
and (c) 700 C and over the Co–Mo/C with the different ratio of Co:Mo (e) 8:2 and (f) 7:3 at 600 C. SEM image of MWCNTs formed by the ethanol
ꢀ
over the Co (5 wt%)/C at 600 C (d).
4390
J. Nanosci. Nanotechnol. 18, 4387–4392, 2018

Diao et al.
Hydrogen and Carbon Nanotubes Production by Catalytic of Ethanol Over the Co–Mo Catalysts
(b)
(a)
Co-Mo(Co:Mo= 9:1)/C
500 ºC
6
00 ºC
Co:Mo=9:1
5
7
00 ºC
00 ºC
Co:Mo=8:2
Co:Mo=7:3
1
000 1100 1200 1300 1400 1500 1600 1700 1800
1000 1100 1200 1300 1400 1500 1600 1700 1800
Raman shift / cm–1
Raman shift / cm–1
Figure 6. (a) Raman of MWCNTs formed by the ethanol decomposition over the Co–Mo (Co:Mo = 9:1)/C catalysts at different with temperatures:
ꢀ
5
(
00, 600 and 700 C and (b) Raman of MWCNTs formed by the ethanol decomposition over the Co–Mo/C catalysts with the different ratio of Co:Mo
ꢀ
9:1, 8:2 and 7:3) at 600 C.
formation.36 At 600 C, with the ratio of Co:Mo decreas-
ing from 9:1 to 7:3, the density of CNTs declined over the
Co–Mo/C catalyst in the Figures 4(e) and (f). High con-
centration of Mo resulted in increasing the CoO crystallites
had a negative effect on the quality of CNTs.38 Therefore,
the Co–Mo/C catalyst was the most effective for produc-
ꢀ
could be evaluated via the intensity ratio of G and D band.
A larger I /ID ratio conformed to high purity and less
G
4
2ꢀ43
defects in sidewall of CNTs.
Figure 6(a) showed the
Raman spectra of CNTs were synthesized over Co–Mo
ꢀ
(Co:Mo = 9:1)/C at 500, 600 and 700 C. It was signifi-
cant that the I
/I
ratio of CNTs in the temperature order
G
D
ꢀ
ꢀ
ꢀ
ꢀ
ing CNTs at 600 C and the optimal molar ratio of Co:Mo
600 C (I
G
/I
D
= 4ꢅ5) > 500 C (I
G
/I
D
= 4) > 700 C
was 9:1.
(I
G
/I
D
= 2ꢅ5), indicating the optimal reaction temperature
ꢀ
Based on the diffraction angles of the X-ray scattered,
X-ray crystallography determines the crystal phases of
the catalyst due to different arrangement of atoms in the
crystals. The XRD profiles of CNTs was observed grown
was 600 C. Figure 6(b) showed Raman spectra of CNTs
were produced by ethanol decomposition over Co–Mo/C
catalysts with the Co:Mo ratio of 9:1, 8:2 and 7:3 at
ꢀ
6
00 C. CNTs with Co–Mo/C (Co:Mo = 9:1) (I /I = 4ꢅ5)
G
D
IP: 188.72.126.53 On: Mon, 17 Sep 2018 06:44:41
and Co–Mo/C (Co:Mo = 8:2) (I /I = 2ꢅ5) loading had
over the Co–Mo (Co:Mo = 9:1)/C cat Ca l oy sp t ys r fi go hr t6: 0A mm ien ri ac ta n Scientific Publishers
G
D
ꢀ
00 C in the Figure 5. It could be seen that tDh ee li pv ee ar ke d by Ingenta
higher G peak and I /I than Co–Mo/C (Co:Mo = 7:3)
G
D
6
ꢀ
ꢀ
(
9
I /I = 2). The result demonstrated Co–Mo (Co:Mo =
appears at 2ꢄ = 26 and 54.4 , corresponding to the (002)
G
D
3
9
:1)/C catalyst was the most effective catalyst for CNTs
and (100) reflection of the graphite. In addition, the peak
ꢀ
40
growth from ethanol decomposition, with higher graphiti-
zation and lower defects of CNTs deposited over Co–Mo
appears at 2ꢄ = 44ꢅ7 attributed to the Co O . The char-
3
4
ꢀ
ꢀ 41
acteristic pattern of the MoO was 29.1 and 34.5 . The
3
(
Co:Mo = 9:1)/C catalysts.
reason may be that the addition of Mo to Co forms MoO3,
which prevented the extensive agglomeration of Co species
during the narrow diameter of CNTs synthesis.
Figure 6 illustrates Raman spectra of CNTs were formed
by ethanol decomposition over the Co–Mo/C catalysts. For
all the Raman spectra, two bands were observed at 1590
Figure 7 represented in the TEM images, the CNTs
3
8
synthesized were MWCNTs with the use of ethanol as
a carbon source and Co–Mo (Co:Mo = 9:1)/C as cata-
lysts. From Figure 7(a), TEM studies showed metallic Co
nanoparticles were obvious at the tips of the CNTs and the
catalyst particles on a long CNTs tip were almost encap-
−1
(
G band) and 1350 (D band) cm . The structure of CNTs
4
4
sulated by the grapheme layers. CNTs were observed
ꢀ
formed at 600 C with an inner diameter of 15–20 nm
(
a)
(b)
and outer diameter of 25–30 nm. The amorphous carbon
ꢀ
deposited over the Co–Mo/C catalysts at 700 C in the
Figure 7(b). Considering the quality of CNTs, the optimal
ꢀ
reaction temperature was 600 C.
4
. CONCLUSIONS
In the present work, ethanol decomposition over Co–Mo/C
catalysts with different Co:Mo molar ratios were inves-
ꢀ
2
00nm
tigated in the temperature range of 500–700 C. The
2
00nm
2
0 nm
effects of temperature and the molar ratio of Co:Mo on
the hydrogen production, as well as CNTs growth has
been discussed systematically. The optimal experiment
conditions for hydrogen production and the growth of
Figure 7. TEM of MWCNTs formed by the ethanol decomposition
over the Co–Mo (Co:Mo = 9:1)/C catalysts at different with tempera-
ꢀ
ꢀ
tures: (a) 600 C and (b) 700 C.
J. Nanosci. Nanotechnol. 18, 4387–4392, 2018
4391

Hydrogen and Carbon Nanotubes Production by Catalytic of Ethanol Over the Co–Mo Catalysts
Diao et al.
CNTs were also obtained. The Co–Mo (Co:Mo = 9:1)/C
21. A. I. Yardimci, S. Yılmaz, and Y. Selamet, Diamond Related Mate-
rial 60, 81 (2015).
catalysts was the most effective catalyst based on the
22. E. V. Lobiak, E. V. Shlyakhova, L. G. Bulusheva, P. E. Plyusnin,
Y. V. Shubin, and A. V. Okotrub, Journal of Alloy Compounds
hydrogen yield (84%) and the high quality of CNTs at
ꢀ
6
00 C. The resulted also suggested that a small amount
621, 351 (2015).
of Mo helps in dispersing active metal precursor at higher
23. I. Dincer, Int. J. Hydrogen Energy 27, 265 (2002).
ꢀ
temperature of 600 C, which were active for CNTs growth
24. M. Barroso, M. Gomez, L. Arrúa, and M. Abello, Reaction Kinetics,
Mechanisms and Catalysis 115, 535 (2015).
and H yield.
2
2
5. P. Y. Sheng, A. Yee, G. A. Bowmaker, and H. Idriss, J. Catal.
08, 393 (2002).
2
Acknowledgments: Project supported by was sup-
ported by the financial supports of the National Nature
Science Foundation of China (No. 51672213).
26. T. Davidian, N. Guilhaume, E. Iojoiu, and H. Mirodatos, Applied
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27. K. Faungnawakij, Y. Tanaka, N. Shimoda, T. Fukunaga, R. Kikuchi,
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Received: 14 January 2017. Accepted: 3 July 2017.
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