Preparation and characterization of highly efficient cufe mixed oxides for total oxidation of toluene

Article abstract of DOI:10.1166/jnn.2018.14627

In this study, Cu/Fe type mixed oxides catalysts with different ratios of metal irons are successfullysynthesized via fixed hydrothermal treatment. The prepared samples were then characterized bya combination of several techniques, such as XRD, BET, SEM, H₂-TPR and FT-IR. The catalyticactivity enhanced with the increasing amount of Cu in the HT-precursors, but it decreases whenthe ratio of Cu/Fe is above 4. The influence of calcination temperature was also studied in thesearch of highly dispersed active catalysts. The catalytic test indicated that the Cu/Fe mixed oxidespossessed outstanding highly activity towards toluene oxidation. The highest catalytic activity wasexhibited by Cu₄Fe-400 of which the T₅₀ and T₉₀ reaches at about 258 °C and 294 °C respectively.

Full text of DOI:10.1166/jnn.2018.14627

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 3381–3386, 2018
Copyright © 2018 American Scientific Publishers
All rights reserved
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Printed in the United States of America
Preparation and Characterization of Highly Efficient CuFe
Mixed Oxides for Total Oxidation of Toluene
Tianshan Xue1, Renna Li1, Wanlin Gao1, Yanshan Gao1, Qiang Wang1ꢀ∗, and Ahmad Umar2ꢀ3ꢀ∗
1College of Environmental Science and Engineering, Beijing Forestry University, Haidian District, Beijing 100083, P. R. China
2Department of Chemistry, College of Science and Arts, Najran University, Najran-11001, Kingdom of Saudi Arabia
3Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, Najran-11001, Kingdom of Saudi Arabia
In this study, Cu/Fe type mixed oxides catalysts with different ratios of metal irons are successfully
synthesized via fixed hydrothermal treatment. The prepared samples were then characterized by
a combination of several techniques, such as XRD, BET, SEM, H2-TPR and FT-IR. The catalytic
activity enhanced with the increasing amount of Cu in the HT-precursors, but it decreases when
the ratio of Cu/Fe is above 4. The influence of calcination temperature was also studied in the
search of highly dispersed active catalysts. The catalytic test indicated that the Cu/Fe mixed oxides
possessed outstanding highly activity towards toluene oxidation. The hꢀighest catalytic activity was
ꢀ
exhibited by Cu4Fe-400 of which the T50 and T90 reaches at about 258 C and 294 C respectively.
Keywords: Mixed Oxides, VOC Oxidation, Copper Oxides, Hydrothermal Synthesis.
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1. INTRODUCTION
for VOC catalytic combustion. Interaction between active
components in mixed metal oxides catalysts touches off
structural and thermal stabilization and the catalysts dis-
play a higher surface area than that of pure metal oxides.
An impactful way to attain mixed oxides catalysts is
to utilize hydrotalcites (HTs) or layered double hydrox-
ides (LDHs) as precursors. Layered double hydroxides
Volatile organic compounds (VOC) emitted by various
industrial processes and automotive exhausts have been
identified as being responsible for ground level smog
formation and carcinogenic effects in humans.1 Many
technologies have been proposed and applied for VOC
removal including adsorption, thermal oxidation and cat-
alytic oxidation.2 Among the various methods, catalytic
oxidation has been widely utilized as a consequence of its
low toxic fumes products, low cost and high efficiency.3
Therefore, highly active catalysts especially operating at
lower temperatures are required.4
Noble metals and transition metals are the two groups
of catalysts which were widely used for the total oxidation
of VOC. Pt-based catalysts have played a dominant role
in the industrial catalytic oxidation of VOCs due to their
outstanding catalytic performance. Classically, the active
metal oxides need to be deposited on a suitable support
with good thermal stability and high surface area. Alu-
mina (Al2O3ꢀ,5ꢁ6 titania (TiO2ꢀ,7 MgO,8 CeO2 and carbon
based materials9ꢁ10 are some of the supports in common
use. Among them, ꢂ-Al2O3 is one of most universal sup-
ports for both laboratories and factories. Many research
groups have found that mixed metal oxides were effective
(LDH) is a type of anionic clay, with a general formula
2+
of [M Mx3+(OH)2]z+[An−
]
z/n ·mH2O where M2+ (M2+
=
1−x
Mg2+, Zn2+, Ni2+, Co2+, Cu2+, and Mn2+, etc.) and M3+
(M3+ = A13+, Cr3+, Mn3+, and Fe3+, etc.) are divalent and
trivalent cations.11–13 LDHs, directly prepared or thermal
treated, both are promising materials for a large amount of
practical applications in catalysis,14 adsorption,15 pharma-
ceutics, photochemistry, electrochemistry and other areas.
In recent years, the application of LDHs derived mixed
oxides as VOC catalyst has attracted widespread attention.
The Cu-containing oxide systems belong to the most
active catalysts of VOCs abatement. Several factors
affect the performance of CuO in the oxidation progress to
VOC, the lattice oxygen in CuO also plays an active role
and the rate of oxidation becomes limited with the deple-
tion of lattice oxgyen.16 Cordi17 synthesized a CuO/Al2O3
catalyst and tested the dehydrogenate and oxidation activ-
ity to various VOCs such as formic acid, methanol and
acetaldehyde.
∗Authors to whom correspondence should be addressed.
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Preparation and Characterization of Highly Efficient CuFe Mixed Oxides for Total Oxidation of Toluene
2.3. Sample Characterization
Xue et al.
Few Cu-containing oxide catalysts derived from
hydrotalcites-like precursors have been investigated.
A binary Cu/Mn oxides catalysts have been synthesized
and characterized by Machej et al.18 Catalytic activity of
mixed oxides catalyst derived from Cu4Mn4Al1-HTs for-
mulation by the addition of Zr and Ce towards methane
combustion exhibits a T50 temperature as 401 ꢀC. The
addition of Ce and Zr hinders the evolution of spinel
phase upon calcination and helps to maintain the spread-
ing of the active phase. Mixed oxides of Cu/Mn/Mg/Al
and Co/Mn/Mg/Al were obtained by means of the thermal
decomposition of hydrotalcites and evaluated in the total
oxidation performance of toluene, ethanol and butanol.19
The catalysts of the Cu/Mn series show more crystalline
structure than the solids of Co/Mn series and the cooper
together with the manganese promotes the formation of
phases of low crystalline structure and optimizes the
redox properties of the materials. Different Cu/Mg/Al-HTs
derived catalysts prepared by co-precipitation method were
produced by Kovanda et al.20 The oxidation activity in
the toluene oxidation increased with increasing amount of
Cu2+ in the solids and corresponded with the amount of
easily reducible cooper component.
X-ray diffraction analysis of CuxFe-HTs and Cu4Fe-MOs
were recorded on a Shimadzu XRD-7000 diffract meter
instrument in reflection mode with Cu Kꢃ radiation in the
2ꢄ range from 10ꢀ to 80ꢀ with a scanning rate of 5ꢀ min−1
(40 KV, 30 mA). Size and morphology of the sample
grains were measured sing scanning electron microscopy
(SEM, S-3400N II). The specific surface area was cal-
culated from Brunauer–Emmett–Teller (BET, SSA-7000)
method using the adsorption branch acquired at a relative
pressure (P/P0) range of 0.05–0.30. The temperature pro-
grammed reduction of hydrogen (H2-TPR) was tested on
a chemisorption analyzer (PCA-1200). After pretreated at
ꢀ
ꢀ
400 C for 3 hours, each sample was cooled to 50 C in a
flow of N2. Andꢀthe reduction of the samples was initiated
from 50 to 700 C with a mixture of 10% H2/Ar at a rate
ꢀ
of 10 C/min.
2.4. Catalytic Oxidation of Toluene
The evaluation of the catalytic activity was conducted in
a fixed-bed micro reactor. The composition of the reac-
tant mixture was 800 ppm toluene in balanced air, and the
total flow was 100 ml/min. A sample of about 0.1 g is
loaded into the sample container every time the program
The presented work deals with the synthesis and
characterization of Cu/Fe-mixed oxides catalysts derived
from hydrotalcites precursors which have not been far
researched as toluene oxidation catalyst before. BET,
ꢀ
is run. The range of test temperatures was 30 to 400 C
ꢀ
with a heating rate of 2 C/min. The concentrations of the
reactants and products were monitored on line by a gas
chromatograph (Agilent 7890B) equipped with FID detec-
tors. The toluene conversion rate was characterized by the
following Eq. (1), where Ctoluene and Ct∗oluene are the initial
and treated concentration of toluene. The CO2 concentra-
tion was detected by the FID detector equipped with a
nickel conversion furnace.
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XRD, SEM and H2-TPR techniques were used to exam-
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ine the physicochemical states. The aim was to evaluate
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the effect of metal ratio and calcination temperature of
catalysts on their physical properties and performance in
combustion of toluene.
Toluene conversion rate=ꢅ1−Ctoluene/Ct∗olueneꢀ×100%
2. EXPERIMENTAL SECTIONS
2.1. Materials
(1)
All the chemicals used in this study were of analyt-
ical grade and used as receive without further purifi-
cation. Copper nitrate (Cu(NO3ꢀ2 · 3H2O), ferric nitrate
(Fe(NO3ꢀ3 ·9H2O) were obtained from commercial source.
Deionized water was utilized in all the experimental
processes.
3. RESULTS AND DISCUSSION
3.1. Characterization of Catalysts
To clarify the details of the key factors determining the
performance of the CuFe-HT, we systematically studied
the influence of different Cu/Fe ratio and calcine tempera-
ture using XRD, SEM, BET, FT-IR and H2-TPR analyses
which will be presented as follows.
The XRD patterns of CuxFe-HTs are shown in
Figure 1(a), exhibiting the characteristic HTs reflections
for the basal (003), (006), (009) and (110) in all of the
samples. These diffractions are shifted to higher angles
compared to typical HTs (JCPDS: 41-1428) because of the
distortion of the copper sites, which is caused by Jahn–
Teller effect of Cu2+ (d9).21 Trace of Cu2(NO3ꢀ(OH)3
(JCPDS: 78-2177) impurities is also observed.22 It is note-
worthy that when the x (ratio of Cu/Fe) < 3, the peaks
(003), (006) are weak and narrow implying that the lay-
ered structures are not well-formed. And when x > 4, the
2.2. Sample Preparation
A series of CuxFe-HT precursors with different value
of x were synthesized by means of a fixed hydrother-
mal method. A solution containing appropriate quantities
of Cu(NO3ꢀ2 · 3H2O, Fe(NO3ꢀ3 · 9H2O was added slowly
under magnetic stirrer into Na2CO3 solution. The pH was
ꢀ
adjusted to 4.6 by the addition of NaOH under 80 C oil
bath. After 30 minutes aged, the solution was placed in
autoclave bombs and heated at 120 ꢀC for 24 h. The prod-
ucts were filtered, washed with deionized water and dried
in air. The dried precipitate was calcined at various tem-
peratures, assigned as CuFe-MOs or CuFe-300, CuFe-400
and CuFe-500.
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Xue et al.
Preparation and Characterization of Highly Efficient CuFe Mixed Oxides for Total Oxidation of Toluene
Figure 2. XRD patterns of Cu4Fe-HTs pretreated under different
temperatures.
in Cu4Fe-500 which may cause the decline of the sample
activity.
The SEM images of Cu4Fe-HTs and Cu4Fe-400 have
been taken for a further understanding of the structure and
surface morphology of Cu4Fe-HTs and its derived metal
oxides as shown in Figure 3. The Cu4Fe-HTs presents a
layered structure in many irregular shaped particles. And
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the Energy Dispersive X-ray (EDX) analysis of Cu4Fe-400
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Figure 1. XRD patterns of (a): CuxFe-HTs, (b): CuxFe-400.
stray peaks begin to appear and the structure of the prod-
ucts is no longer singular. However, the XRD patterns in
Figure 2(b) show the significant changes of the samples
ꢀ
after 400 C calcination, the intense X-ray reflections at
2ꢄ = 11ꢆ4 disappeared, the diffraction peak observed at
35.5 and 38.7 are respectively attributed to the (311) plane
of CuFe2O4 and CuO phase, indicating the formation of
CuFe2O4 and CuO phase in the CuxFe-MOs samples.23
Since the Cu/Fe ratio of 4 appeared to be the most ade-
quate to obtain a highly crystalline hydrotalcites material,
samples synthesized in this condition were tested to search
the best calcination temperature of the samples.
Figure 2 shows the XRD profile of the Cu4Fe-HTs un-
calcined and pretreated under different calcination tem-
peratures. The Cu4Fe-400 and Cu4Fe-500 both exhibit a
well-crystallized structure than that of Cu4Fe-300 on the
basis of the sharp and intense peaks at 35.5ꢀ and 38.7ꢀ. On
the other hand, few undesired peaks have been observed
Figure 3. SEM images of (a) Cu4Fe-HTs and (b) Cu4Fe-400.
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Preparation and Characterization of Highly Efficient CuFe Mixed Oxides for Total Oxidation of Toluene
Xue et al.
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Figure 4. Isotherms N2-adsorption desorption and pores distribution of
Cu4Fe-HTs and Cu4Fe-MOs.
Figure 5. FT-IR analysis of CuxFe-HTs and Cu4Fe-MOs.
clearly showed the presence of Cu and Fe. The charac-
teristic platelet feature of Cu4Fe-HTs is retained during
the heating progress, and the surface turns to be cras-
situde for the reconstruction of the hydrotalcite struc-
ture and the evaluation of the sample morphology. The
fragmented surface may result in a higher surface area,
which could be simultaneously supported by the BET
results.
For all the samples, the N2-adsorption desorption
isotherms shown in Figure 4(a) are of type IV, which
exhibits aspects of mesoporous materials. The adsorption
capacity increases rapidly at lower relative pressure (<0.1
p/p0) and the curve is convex for the strong interac-
tion of the surface adsorbent. Then the curve is raised
again and the adsorption hysteresis loop appears in the
middle section, which corresponds to the capillary con-
densation system of porous adsorbent.24 It is noted that
the N2-adsorption desorption isotherms of Cu4Fe-300 and
Cu4Fe-400 have a more distinct adsorption hysteresis loop,
which means quite a lot of mesoporous exist in the
materials.25
FT-IR analysis has been used to explore the interlayer
anion, lattice oxygen and hydration water of CuxFe-HTs
and Cu4Fe-MOs. In Figure 5(a), a broad band centered at
around 3452 cm−1 is attributed to the OH stretching vibra-
tion of interlayer water and hydroxyl groups on the layers.
The vibration of carbonate ions is detected at 1328 cm−1
and the adsorption at about 440–667 cm−1 is considered
as the skeletal vibration of CuFe-HTs. In all the samples
of different Cu/Fe ratios, the locations of the peaks have
no significant changes, though the peak shapes changed
demonstrating that there is a certain effect of metal content
on the interaction force between ions.
H2-temperature programmed reduction (H2-TPR) analy-
sis of Cu4Fe-MOs calcined at different temperatures were
carried out to investigate the reducibility of the mixed
oxides catalysts, which was considered to be an important
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Xue et al.
Preparation and Characterization of Highly Efficient CuFe Mixed Oxides for Total Oxidation of Toluene
Table I. T50 and T90 of CuxFe-MOs for toluene oxidation.
Cu/Fe
1
2
3
4
5
6
7
T50
T90
313
397
277
390
272
353
258
294
272
365
294
>400
298
>400
3.2. Catalytic Test
CuFe-HTs derived mixed oxides catalysts were calcined
ꢀ
at 400 C and then subjected to catalytic tested in total
oxidation of toluene (Fig. 7), and the temperatures of 50%
(T50) and 90% (T90) toluene conversion were summarized
in Table I. Water and CO2 are the only products in the
whole reaction progress affirmed by the on-line detection
results of a gas chromatographic.
It is evident that the oxidation activity increased with
the increasing amounts of Cu2+ within a certain range
corresponded to the amount of the easily reducible cop-
per component. Upon continued increasing addition of Cu,
the activity tends to decrease as the impurity substance in
hydrotalcites precursors increased according to the XRD
patterns. The effect can be related to the better dispersion
of the active phase in the catalyst obtained from hydro-
talcites precursor. And the highest catalytic activity was
exhibited by Cu4Fe-400 among the CuFe-MOs with vari-
ous Cu contents,ꢀof which the T50 and T90 reaches at about
Figure 6. H2-TPR profiles of Cu4Fe-MOs calcined at different
temperatures.
factor influencing the catalytic activity of the materials. For
all the Cu4Fe-MOs, it is observed at least three reduction
peaks of H2 consumption occurring at 240ꢀ, 276ꢀ and 379ꢀ
in Figure 6. Based on the studies of Dow et al.,26 the peak
may be located at about 246ꢀ due to the reduction of the
highly dispersed cooper oxides that include isolated cooper
ions and small two-three-dimensional clusters. And the
ꢀ
258 C and 294 C respectively.
Figure 8 shows the different calcine temperature of
Cu4Fe-MOs on the toluene oxidation. And the catalytic
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peak centered at about 276ꢀ corresponding to the reduction
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of bulk-like CuO phase. With the elevated amount of Cu,
performances and BET results of Cu4Fe-MOs are listed to
find out the critical factor for toluene oxidation in Table II.
The catalytic oxidation is a kind of surface reaction, thus
the increase of specific surface area (SSA) results in the
enhancement of catalytic activity in general. However, the
catalytic performances of Cu4Fe-MOs calcined at differ-
ent temperature were not well fitted for this regular pat-
tern. Cu4Fe-300 has a biggest specific surface area equals
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the peaks occurred under 300 ꢀC tend to be broader, which
is in good agreement with XRD patterns showing that the
crystallites size effects the reduction iꢀntensively.ꢀThe wide
peaks take place in the range of 500 C to 700 C, which
might be attributed to the reduction of Fe3+ to Fe2+ 27
.
Results confirm that the observed peaks are mainly related
to the copper species reduction.
Figure 7. The influence of different ratio of Cu and Fe on the toluene
Figure 8. The influence of different calcine temperature of Cu4Fe-MOs
oxidation activity.
on the toluene oxidation.
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Preparation and Characterization of Highly Efficient CuFe Mixed Oxides for Total Oxidation of Toluene
Xue et al.
Table II. T50 and T90 volumes and BET results of Cu4Fe-HTs and
Cu4Fe-MOs.
References and Notes
1. P. Papaefthimiou, T. Ioannides, and X. E. Verykios, Appl. Catal. B
Environ. 13, 175 (1997).
Pore
size (nm)
Pore
SSA
T50
(ꢀC)
T90
(ꢀC)
2. M. S. Kamal, S. A. Razzak, and M. M. Hossain, Atmos. Environ.
140, 117 (2016).
Sample
volume (cm2/g)
(m2/g)
3. J. J. Spivey, Ind. Eng. Chem. Res. 26, 2165 (1989).
4. H. Huang, Y. Xu, Q. Feng, and D. Y. C. Leung, Catal. Sci. Technol.
5, 2649 (2015).
5. C. H. Wang, Chemosphere 55, 11 (2004).
6. S. M. Saqer, D. I. Kondarides, and X. E. Verykios, Appl. Catal. B
Environ. 103, 275 (2011).
Cu4Fe-300
Cu4Fe-400
Cu4Fe-500
Cu4Fe-HTs
7ꢆ3
9ꢆ67
13ꢆ49
4ꢆ09
0ꢆ195658
0ꢆ1817
0ꢆ088045
0ꢆ168246
53.613
37.573
13.057
82.348
273
258
256
/
342
294
332
/
7. J. M. Coronado, C. Belver, C. Y. Lee, and V. Augugliaro, Appl.
Catal. B Environ. 29, 327 (2001).
8. M. H. Castaño, R. Molina, and S. Moreno, J. Mol. Catal. A Chem.
398, 358 (2015).
9. K. H. Chuang, Z. S. Liu, C. Y. Lu, and Y. W. Ming, Ind. Eng. Chem.
Res. 48, 4202 (2009).
10. S. Jiang, E. S. Handberg, F. Liu, Y. Liao, H. Wang, Z. Li, and
S. Song, Appl. Catal. B Environ. 160, 716 (2014).
11. Q. Wang, S. Tang, L. Edward, and O. Dermot, Nanoscale 5, 114
(2012).
12. Q. Wang and O. Dermot, Chem. Rev. 112, 4124 (2012).
13. G. Centi, G. Fornasari, C. Gobbi, M. Livi, F. Trifirò, and A. Vaccari,
Catal. Today 73, 287 (2002).
14. Z. Wang, P. Lu, X. Zhang, L. Wang, Q. Li, and Z. Zhang, Rsc Adv.
5, 65 (2015).
15. Q. Wang, Z. Wu, H. Tay, L. Chen, Y. Liu, J. Chang, Z. Zhong,
J. Luo, and A. Borgna, Catal. Today 164, 198 (2011).
16. E. Heracleous, A. F. Lee, K. Wilson, and A. A. Lemonidou, J. Catal.
231, 159 (2005).
17. E. M. Cordi, P. J. O’Neill, and J. L. Falconer, Appl. Catal. B Environ.
14, 23 (1997).
53.613 m2/g, but the T50 and T90 are lower than that of
Cu4Fe-400. This appearance indicates that the SSA of cat-
alysts is not the dominant factor that affects the oxida-
tion performance. The adsorbed oxygen in surface oxygen
species and acid site amount seem to be the determinant
factor for Fe-supported catalyst.28
4. CONCLUSIONS
In this study Cu/Fe hydrotalcites precursors with different
ratio of Cu and Fe have been successfully synthesized and
characterized by XRD, BET, SEM, H2-TPR. All the mate-
rials were active for the total oxidation of toluene after
calcined at different temperatures. It is believed that the
CuFe-MOs have the lower temperature reducibility from
large surface Cu2+ than purity CuO. And there has been a
synergistic effect between Cu and Fe, inducing high sur-
face oxygen species. The Cu/Fe ratio of 4 appeared to be
18. T. Machej, E. M. Serwicka, M. Zimowska, R. Dula, A. Michalik-
IP: 178.250.105.249 On: Fri, 15 Jun 2018 07:22:10
the most adequate to obtain a highly crystalline hydro-
Zym, B. Napruszewska, W. Rojek, and R. Socha, Appl. Catal. A
Gen. 474, 87 (2014).
Copyright: American Scientific Publishers
talcites material. In addition, it is noted that the catalytic
activity enhanced with the increasing amount of Cu in the
HT-precursors, but it decreases when the ratio of Cu/Fe is
above 4. The N2-adsorption desorption isotherms of Cu4Fe-
300 and Cu4Fe-400 have a more distinct adsorption hys-
teresis loop, which means quite a lot of mesoporous exist
in the material. The highest catalytic activity was exhibited
by Cu4Fe-400 of which the T50 and T90 reaches at about
258 ꢀC and 294 ꢀC respectively. Calcination at 500 ꢀC leads
to a certain degree of inactivation of the catalyst.
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19. D. A. Aguilera, A. Perez, R. Molina, and S. Moreno, Appl. Catal. B
Environ. 104, 144 (2011).
20. F. Kovanda, K. Jirátová, J. Rymeš, and D. Koloušek, Appl. Clay Sci.
18, 71 (2001).
21. H. Yan, J. Lu, M. Wei, J. Ma, H. Li, J. He, D. G. Evans, and X. Duan,
J. Mol. Struc. Theochem. 866, 34 (2008).
22. H. Liu, Q. Jiao, Y. Zhao, H. Li, C. Sun, X. Li, and H. Wu, Mater.
Lett. 64, 1698 (2010).
23. D. Dumbre, V. R. Choudhary, and P. R. Selvakannan, Polyhedron
120, 180 (2016).
24. K. Morishige and M. Shikimi, J. Chem. Phys. 108, 7821 (1998).
25. K. S. W. Sing, Pure Appl. Chem. 57, 603 (2009).
26. W. P. Dow, Y. P. Wang, and T. J. Huang, Appl. Catal. A Gen. 190, 25
(2000).
27. L. Wang, J. Chen, H. Watanabe, Y. Xu, M. Tamura, Y. Nakagawa,
and K. Tomishige, Appl. Catal. B Environ. 160, 701 (2014).
28. X. Liang, F. Qi, P. Liu, G. Wei, X. Su, L. Ma, H. He, X. Lin, Y. Xi,
and J. Zhu, Appl. Clay Sci. 132–133, 96 (2016).
Acknowledgments: This work was supported by the
Fundamental Research Funds for the Central Universities
(2016ZCQ03), the National Natural Science Foundation of
China (51622801, 51572029), and the Beijing Excellent
Young Scholar (2015000026833ZK11).
Received: 21 December 2016. Accepted: 23 March 2017.
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