Ionic self-assembly affords mesoporous ionic networks by crosslinking linear polyviologens with polyoxometalate clusters

Article abstract of DOI:10.1039/c6dt00070c

Ionic-bonded mesoporous ionic networks were prepared by the ionic self-assembly of polyoxometalate (POM) clusters with linear cationic polyviologens in water. The POM-enriched PMIN-2(V) possesses a high surface area up to 120 m² g^-1, exhibiting superior non-noble metal heterogeneous catalytic performance in the ambient aerobic selective oxidation of 5-hydroxymethylfurfural.

Full text of DOI:10.1039/c6dt00070c

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DOI: 10.1039/C6DT00070C
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Ionic self-assembly affords mesoporous ionic networks by
crosslinking linear polyviologens with polyoxometalate clusters
Guojian Chen,a,b Wei Hou,a Jing Li,a Xiaochen Wang,a Yu Zhou*a and Jun Wang*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Ionic-bonded mesoporous ionic networks were prepared by the molecular or atomic level to the nano and even to the micrometer
ionic self-assembly of polyoxometalate (POM) clusters with linear scale.14 They have been widely used as nanoscale building blocks for
cationic polyviologens in water. The POM-enriched PMIN-1(V) constructing various supermolecular materials, enabling the facile
possesses a high surface area up to 120 m2 g-1, exhibiting superior preparation of uniform self-supported functional materials with
non-noble metal heterogeneous catalytic performance in the high POM density towards a large domains of applications.14,15 Both
ambient aerobic selective oxidation of 5-hydroxymethylfurfural.
order and disorder POM based supermolecular assemblies were
reported by self-assembly approach,16 but majority of them were
nonporous structure or possessed low surface area,17-20 limiting
their performance in the processes involving mass transfer step
such as catalysis, one main application of POMs.
Functional porous materials have received ever-increasing attention
because of their wide applications in adsorption, separation,
catalysis, energy storage, electrode materials, etc.1-11 Self-assembly
method enables the facilely and elegantly fabrication of numerous
versatile porous materials from diverse molecular building blocks,
and has become a hot topic in chemical and materials science.
Different driving forces afford different series of porous materials.
For instance, it is feasible to self-assembly synthesis of metal-
organic frameworks (MOFs) by coordination bonds,2 crystalline
covalent organic frameworks (COFs) and amorphous porous organic
polymers (POPs) by covalent bonds,3,4 and hydrogen-bonded
organic frameworks (HOFs) via weaker hydrogen-bonding
interactions.5,6 Nonetheless, as a large class of widely applied
materials, ionic bonded inorganic or inorganic/organic hybrid salts
are scarcely prepared to possess large open porous networks. To
the best of our knowledge, no such type porous ionic-bonded
frameworks attains through ionic bond derived self-assembly
method, i.e. the ionic self-assembly (ISA) approach,12 despite that
In this work, we try to apply ISA strategy towards self-assembled
porous ionic networks by the cooperative combination of linear
cationic polymers and multivalent anionic building blocks. A series
of novel POM-based mesoporous ionic networks (shorten as PMINs)
are constructed by crosslinking linear cationic polyviologens with
POM anionic clusters via ionic-bonding interactions. Polyviologens
containing 1,1′-dialkyl-4,4′-bipyridinium repeated units are a well-
known class of cationic polymers with photoelectrochromism,
electron-accepting ability and redox activity.21,22 This tactic could in-
situ incorporate catalytically active POM building blocks and redox
viologen units into the resulted PMINs, simultaneously reaching
organic-inorganic hybrid mesoporous ionic nanostructures with
unprecedented high surface areas (120 m2 g-1) and available redox
catalytic properties. Thus, the typical PMo10V2O405- (PMoV)-enriched
PMINs act as highly efficient heterogeneous catalysts in the
ambient selective aerobic oxidation of 5-hydroxymethylfurfural into
2,5-diformylfuran with molecular oxygen (O2).
Scheme 1 illustrates the synthetic process for PMoV-based
mesoporous ionic networks PMIN-x(V) by using different
polyviologens [PMV]Br2, [PEV]Br2 and [PBV]Br2 for x=1, 2 and 3
respectively. Three new alkyl-linked polyviologens are prepared by
the quaternization reaction of 4,4´-bipyridine with dibromoalkane.21
The resulted water-soluble linear polymers polyviologens have
repeat cationic units of 4,4´-bipyridinium with alkyl linkers, as
confirmed by 1H NMR, 13C NMR, FT-IR spectra and elemental
analysis (Figs. S1-S3 and S6). The molecular weights (Mw) of
[PMV]Br2, [PEV]Br2 and [PBV]Br2 are 19948, 19810 and 19694 Da,
respectively (Fig. S7). Electrostatic interactions induced ionic self-
assembly between the above three polyviologens and PMoV anions
ISA achieves various success as
a powerful tool to afford
hierarchical nanostructured materials by the electrostatic coupling
of carefully chosen charged surfactants or polymers and oppositely
charged building blocks.12,13
Polyoxometalates (POM) are an outstanding family of structurally
diverse anionic metal-oxo clusters with tunable engaging physical
and chemical properties by structure designation from the
a State Key Laboratory of Materials-Oriented Chemical Engineering, College of
Chemical Engineering, Nanjing Tech University, Nanjing, 210009, China. E-mail:
njutzhouyu@njtech.edu.cn, junwang@njtech.edu.cn; Tel: +(86) 25-83172264. b
School of Chemistry and Chemical Engineering, Jiangsu Normal University, Xuzhou,
221116, China.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [Experimental section,
Figures S1-S16, Tables S1-S3 and Scheme S1]. See DOI: 10.1039/x0xx00000x.
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summarized in Table S2. Noticeably, those inorVgiaewniAcrticcleaOtinolinnes
modified POMs were usually of microporoDusOIs:t1r0u.c10tu3r9e/Cs 6wDiTth00s0m70aCll
amount of mesopore. It is the first time to achieve such abundant
mesopores over self-assembled POMs, endowing high POM anions
density on the surface of a homogeneous framework.
Scheme 1 Synthetic process for constructing PMINs from ionic self-
assembly of cationic polyviologens and PMoV in aqueous solution.
in aqueous solution affords three PMIN-x(V) samples. Elemental
analysis results in Table S1 provide specific molecular formulas and
chemical compositions for each PMIN sample.
Scanning electron microscopy (SEM) images (Fig. 1A-C and Fig. S8)
reveal that PMIN-x(V) have sponge-like mesoporous structures
derived from the packing of interconnected nanoparticles with the
sizes of about 20-30 nm. PMIN-1(V) has the most loosely-packed
secondary nanostructures, and PMIN-2(V) exhibits moderate spatial
arrangement, while PMIN-3(V) demonstrates closely-packed array.
Mesopores come from the nano-voids among these aggregated
nanoparticles for constructing the crosslinked ionic networks, which
are further confirmed by the results of TEM images (Fig. 1D-F). The
quantitative analysis of the pore structure of above PMIN-x(V)
samples is measured by N2 sorption experiments. Fig. 2 shows that
all the adsorption isotherms are type IV with a clear H1-type
hysteresis loop at the relative pressure (P/P0) range from 0.5 to 0.9,
indicative of typical mesoporous materials. Barrett-Joyner-Halenda
(BJH) pore size distributions of PMIN-x(V) exhibit a very narrow
mesopore size distribution centred at 9.2 nm for PMIN-2 (V), small
mesopore size around 4 nm for PMIN-3(V), and a wide mesopore
size distribution ranging from several to more than ten nm for
PMIN-1(V). The described mesopore sizes of PMIN-x(V) are closely
consistent with the compactness of interconnected particles, as
observed by the SEM and TEM images (Fig. 1A-1F).
Fig. 1 SEM images of (A) PMIN-1(V), (B) PMIN-2(V) and (C) PMIN-
3(V). TEM images of (D) PMIN-1(V), (E) PMIN-2(V) and (F) PMIN-3(V).
(G) Energy-dispersive X-ray spectrometry (EDS) elemental mapping
analysis of the sample PMIN-2(V).
B
0.04
A
PMIN-1(V)
PMIN-1(V)
7.1 nm
100
0.02
15.9 nm
Table 1 list textural parameters including the Brunauer-Emmett-
Teller surface areas (SBET), pore volume (Vp) and average pore sizes
(Dav). The results indicate that PMIN-x(V) have very high BET surface
areas ranging from 72 m2 g-1 to 120 m2 g-1, with the large pore
volume of 0.17-0.28 cm3 g-1. PMIN-2 (V) gives the highest surface
area of 120 m2 g-1, superior to those values (25-51 m2 g-1) of all the
reported porous POM hybrids paired with organic or metal-organic
cations (e.g. triammonium cations,23 ionic liquids,24,25 cationic
transition-metal complexes and zinc phosphate26,27), even surpass
poly(ionic liquid)-supported POMs, 28,29and comparable to the
surface areas (85-156 m2 g-1) for the conventional micro-
0
0.00
0.08
PMIN-2(V)
PMIN-3(V)
PMIN-2(V)
PMIN-3(V)
9.2 nm
100
0.04
0
0.00
0.10
3.7 nm
4.7 nm
100
50
0
0.05
0.00
0.0 0.2 0.4 0.6 0.8 1.0
Relative pressure (P/P0)
10
Pore diameter dp (nm)
Fig. 2 (A) N2 sorption isotherms and (B) Pore size distributions
of PMIN-x(V) samples calculated by BJH method.
+
/mesoporous NH4 and Cs+ salts of POMs.30 Details comparison is
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Table 1 The textural parameters of PMIN-x(V) series materials.
COMMUNICATION
B
A
a
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DOI: 10.1039/C6DT00070C
1061
866
961 785
SBET (m2 g-1)a
Vp (cm3 g-1)b
0.24
Dav (nm)c
13.42
9.33
b
c
PMINs
a
8.65o
PMIN-1(V)
PMIN-2(V)
PMIN-3(V)
72
120
115
d=1.02 nm
b
8.54o
8.27o
d=1.03 nm
0.28
0.17
d
2000
1.2
c
1071
1053
1634
872
785
5.90
d=1.07 nm
d
945
a BET surface area. b Pore volume. c Average pore sizes.
1500
1000
500
10
20
30
40
50
Wavenumbers(cm-1
)
2 Theta (degrees)
3-
C
Besides, another two common POM anions PMo12O40 (PMo)
D
b
a
b
3-
and PW12O40 (PW) are employed as anionic cross-linkers to
a
c
0.8
0.4
0.0
fabricate porous ionic networks. Taking [PMV]Br2 as the linear
cationic polymer, the produced PMIN-1(Mo) and PMIN-1(W) also
demonstrate mesoporous structure with narrow mesopore size
distributions (Fig. S9 and S10). The surface areas for them are 60
and 26 m2 g-1, inferior to the one over PMIN-1(V). The above
phenomena suggest that different mesoporous structure can be
achieved by varying the cations and anions.
d
c
d
400
500
600
700
800
2800
3200
3600
4000
4400
Wavelength (nm)
Magnetic field [G]
F
E
517.0
V2p3/2
O1s
Thermogravimetric (TG) analyses (Fig. S11) of PMIN-x(V) illustrate
their structure stable up to 250 oC. The total weight loss reflects the
high content (71-73 wt %) of PMoV anions within the networks of
PMIN-x(V), close to their theoretical values according to their
molecular formulas obtained from elemental analysis results (Table
S1). PMoV anions in mesoporous ionic networks are investigated by
spectral characterizations (Fig. 3). In Fig. 3A, FT-IR spectra of PMIN-
x(V) show the presence of Keggin-type PMoV cluster by featured
peaks at 1071 and 1053 cm-1 ν(P-Oa), 945 cm-1 ν(M-Ob-M) (M=Mo or
V), 872 cm-1 ν(M-Oc-M) and 785 cm-1 ν(M-Od) with slight shifts
compared with parent H5PMo10V2O40.28 A new broad Bragg peak in
the XRD patterns (Fig. 3B) of PMIN-x(V) appears at 2θ=8.27-8.65o
with the d-spacing values of 1.02-1.07 nm, very close to the primary
unit of PMoV anion. This result indicates that certain ordered
mesostructure forms during the self-assembly process, and PMoV
clusters (ca. 1.0 nm) are homogeneously well-dispersed in the ionic
network, which is further demonstrated by the EDS elemental
mapping analysis for P, O, Mo, V elements (Fig. 1G) and XPS survey
spectrum (Fig. 3E). The electronic behaviours of PMoV-incorporated
PMIN-x(V) are examined by UV-vis, ESR and XPS spectra. The UV-vis
spectra (Fig. 3C) of PMIN-x(V) show apparent enhanced adsorption
bands at 600~800 nm with respect to parent H5PMo10V2O40, which
is assigned to the reduced state of V4+ species. The coexistence of
V5+/V4+ species is further confirmed by the typical eight fold
hyperfine splitting signals centred at G=3500 in ESR spectra (Fig.
3D),10 while the ESR signals for H5PMo10V2O40 are silent. Moreover,
the XPS V2p spectrum confirms the electronic-state of V species, i.e.
the two peaks appeared at 524.3 and 517.0 eV are assigned to
V2p1/2 and V2p3/2; and the adjunctive two peaks appeared at 525.9
and 515.4 eV corresponds to V2p1/2 and V2p3/2, indicating the
present of V5+ and V4+ species, respectively.10 Based on the above
results, π-conjugated redox cationic polyviologens can dramatically
affect the charge state of PMoV anions, promoting the formation of
V4+ species-rich PMIN-x(V), which is beneficial to catalyse many
oxidative reactions.
Mo3p3/2
V2p1/2
524.3
525.9
Mo3d
C1s
N1s
Mo3p1/2
V2p
515.4
P2p
525
520
515
510
800
600
400
200
0
Binding energy (eV)
Binding energy (eV)
Fig. 3 (A) XRD patterns, (B) FT-IR spectra, (C) UV-vis spectra and (D)
ESR spectra of (a) H5PMo10V2O40, (b) PMIN-1(V), (c) PMIN-2(V) and
(d) PMIN-3(V). (E) XPS survey and (F) V2p spectrum of PMIN-2(V).
producing high value-added fine chemicals and functional
polymers.31 Table 2 lists the catalytic performances PMIN-x(V) and
their counterparts in the conversion of HMF to DFF under ambient
O2 condition. It is noteworthy that POM H5PMo10V2O40 is discovered
to be efficient in transforming HMF into DFF, affording a high HMF
conversion of 97.0% and moderate DFF yield of 80.4% under
optimized conditions (Fig. S12). Owing to its soluble in the reaction
solution, H5PMo10V2O40 results a homogeneous catalytic system. By
contrast, all PMIN-x(V) samples resist the dissolution even in DMSO,
thus perform remarkably heterogeneous catalytic activities with
DFF yields of 71.4-86.8%. Among them, PMIN-2(V) gives the highest
HMF conversion of 100%, DFF yield of 86.8%, and turnover number
(TON) of 121. Such catalytic activity is superior to the homogeneous
H5PMo10V2O40, much higher than many vanadium-based catalysts,
and even comparable to noble metal (e.g. Ru) catalysts35,36
32-34
under ambient condition (see Table S3). Importantly, in a five-run
recycling test (Fig. S13), PMIN-2(V) can be directly reused after
facile separation by filtration and maintains initial high activities as
the fresh one, exhibiting well stable reusability. Full
characterizations (FT-IR, N2 sorption and SEM, see Figs. S14-S16) of
the recovered PMIN-2(V) demonstrate the preservation of chemical
composition and porous structure, accounting for its well recycling
performance.
For comparison, parallel tests are carried out on the non-
polymeric viologen-POM ionic hybrid catalysts [Bpy]2.5PMoV2,
[C2Bpy]2.5PMoV2 and [C4Bpy]2.5PMoV2 with similar chemical
compositions as the repeating unit of PMIN-x(V) (see ESI).
Surprisingly, all of them fail to cause heterogeneous systems and
present inferior activities with HMF conversions of 43.6-76.8% and
DFF yields of 39.9-76.6% (Table 2). The above results indicate the
The large surface areas, nanoscale morphologies and high PMoV
contents of mesoporous ionic networks PMIN-x(V) encourage us to
employ them as heterogeneous catalysts in the O2-mediated
oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-
diformylfuran (DFF) , a very important precursor or monomer for
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Table 2 Catalytic performance of PMIN-x(V) and their counterparts
Notes and references
View Article Online
DOI: 10.1039/C6DT00070C
in the ambient aerobic selective oxidation of HMF into DFF.a
1
2
A. G. Slater and A. I. Cooper, Science, 2015, 348, 8075.
H. Furukawa, K. E. Cordova, M. O’Keeffe, O. M. Yaghi, Science,
2013, 341, 1230444.
3
4
5
S. Ding and W. Wang, Chem. Soc. Rev., 2013, 42, 548.
Y. Zhang and S. N. Riduan, Chem. Soc. Rev., 2012, 41, 2083.
Y. He, S. Xiang and B. Chen, J. Am. Chem. Soc., 2011, 133
,
Reaction
system
Homo.
Heter.
Heter.
Heter.
Homo.
Homo.
Homo.
HMF
C (%)b
97.0
80.0
100
97.5
76.8
74.6
43.6
DFF
S (%)c
82.9
89.2
86.8
82.9
99.7
81.7
91.5
DFF
Y (%)d
80.4
71.4
86.8
80.8
76.6
60.9
39.9
Catalyst
TONe
14570.
6
P. Li, Y. He, Y. Zhao, L. Weng, H. Wang, R. Krishna, Hui Wu,
W. Zhou, M. O’Keeffe, Y. Han and B. Chen, Angew. Chem.,
2015, 127, 584.
H5PMo10V2O40
PMIN-1(V)
PMIN-2(V)
112
99
121
112
106
85
7
8
9
S. Fischer, J. Schmidt, P. Strauch and A. Thomas, Angew.
Chem. Int. Ed., 2013, 52, 12174.
Y. Yuan, F. Sun, L. Li, P. Cui and G. Zhu, Nat. Commun., 2014,
5, 4260.
P. Zhang, Z. Qiao, X. Jiang, G. M. Veith and S. Dai, Nano Lett.,
2015, 15, 823.
PMIN-3(V)
[Bpy]2.5PMoV2
[C2Bpy]2.5PMoV2
[C4Bpy]2.5PMoV2
55
a Reaction conditions: HMF (100.8 mg, 0.80 mmol), catalyst (0.01 g,
5.76 μmol based on PMoV), oxygen balloon 1.0 bar, DMSO 4 mL,
120 oC, 3 h. b Conversion (C) of HMF. c Selectivity (S) of DFF. d Yield (Y)
of DFF. e Turnover number (TON): mole of product DFF per mol of
PMoV in the catalyst.
10 G. Chen, Y. Zhou, X. Wang, J. Li, S. Xue, Y. Liu, Q. Wang and J.
Wang, Sci. Rep., 2015, , 11236.
11 X. Wang, Y. Zhou, Z. Guo, G. Chen, J. Li, Y. Shi, Y. Liu and J.
Wang, Chem. Sci., 2015, , 6916.
12 C. F. J. Faul and M. Antonietti. Adv. Mater., 2003, 15, 673.
13 C. F. J. Faul, Acc. Chem. Res., 2014, 47, 3428.
14 Y. Song and R. Tsunashima, Chem. Soc. Rev., 2012, 41, 7384.
15 Y. Zhou, G. Chen, Z. Long and J. Wang, RSC Adv., 2014,
42092.
16 W. Qi and L. Wu, PolymInt, 2009, 58, 1217.
17 T. Lunkenbein, M. Kamperman, Z. Li, C. Bojer, M. Drechsler, S.
Förster, U. Wiesner, A. H. E. Mꢀller and J. Breu, J. Am. Chem.
Soc., 2012, 134, 12685.
18 J. E. Houston, A. R. Patterson, A. C. Jayasundera, W. Schmitt
and R. C. Evans, Chem. Commun., 2014, 50, 5233.
19 N. Liu, H. Wang and W. Bu, J. Mater. Chem. C, 2014,
20 C. Tan, N. Liu, B. Yu, C. Zhang, W. Bu, X. Liu and Y. Song, J.
Mater. Chem. C, 2015, , 2450.
21 A. Factor and G. E. Heinsohn, J. Polym. Sci. B: Poly. Lett.,
1971, , 289.
22 J. Sun and J. Zhang, Dalton Trans., 2015, 44, 19041.
23 M. V. Vasylyev and R. Neumann, J. Am. Chem. Soc., 2004,
126, 884.
5
6
designed alkyl-linked cationic polyviologens play the vital role
towards efficient mesoporous POM-based heterogeneous catalysts
for HMF conversion. Polycaitons enable the heterogeneous
property of PMoV anions through providing strong and complex
interaction between multivalent cations and anions. On the
contrary, dications are incapable to fabricate solid POM catalyst
facing with DMSO as solvent due to the strong solubility of POM in
DMSO, though various dication modified POM solid catalysts have
been achieved by using other solvents. The high catalytic activity,
especially for PMIN-2(V), can be attributed to that large surface
area and abundant mesoporosity allows the well dispersion of V-O-
V (V5+/V4+) catalytically active species and suitable accommodation
for the substrates and products. The proposed catalytic mechanism
for aerobic oxidation of HMF to DFF is presented in Scheme S1 with
the detailed explanation. Owing to the improved mass transfer and
high density of active sites, only small amount of PMIN-x(V) is able
to efficiently convert HMF to DFF, differing from previous reported
catalytic systems for this reaction. Correspondingly, PMIN-2(V)
demonstrates much high TON of 121, greatly exceeding all the
previous non-noble metal catalysts and comparable to the
supported Ru nanoparticles (Table S3).
In summary, POM anions are successfully used as anionic building
blocks for crosslinking cationic polyviologens into a series of novel
mesoporous ionic networks with intrinsic catalytic functionalities.
Large surface area and high density of active sites attains by using
V-containing POM anions. The obtained hybrids perform as highly
efficient and stable heterogeneous catalyst in aerobic oxidation of
HMF to DFF with ambient O2. This work described ionic self-
assembly strategy provides an effective route to versatile porous
POM solid materials, and more ionic cluster-based porous ionic
networks would be rapidly emerged towards diverse applications.
The authors thank greatly the National Natural Science
Foundation of China (Nos. 21136005, 21303084 and 21476109),
Jiangsu Provincial Science Foundation for Youths (No. BK20130921),
Specialized Research Fund for the Doctoral Program of Higher
Education (No. 20133221120002).
4,
2, 5271.
3
9
24 G. Chen, Y. Zhou, P. Zhao, Z. Long and J. Wang,
ChemPlusChem, 2013, 78, 561.
25 G. Chen, Y. Zhou, Z. Long, X. Wang, J. Li and J. Wang, ACS
Appl. Mater. Interfaces, 2014, 6, 4438.
26 S. Uchida, S. Hikichi, T. Akatsuka, T. Tanaka, R. Kawamoto, A.
Lesbani, Y. Nakagawa, K. Uehara and N. Mizuno, Chem.
Mater.,2007,19,4694.
27 A. C. Kalita, C. R. Marchal and R. Murugavel, Dalton Trans.,
2013, 42, 9755.
28 P. Zhao, Y. Leng and J. Wang, Chem. Eng. J., 2012, 204-206
,
72.
29 C. Gao, G. Chen, X. Wang, J. Li , Y. Zhou and J. Wang, Chem.
Commun., 2015, 51, 4969.
30 K. Inumaru, Catal. Surv. Asia, 2006, 10, 151.
31 R.-J. van Putten, J. C. van der Waal, E. de Jong, C. B.
Rasrendra, H. J. Heeres and J. G. de Vries, Chem. Rev., 2013,
113, 1499.
32 I. Sádaba, Y. Y. Gorbanev, S. Kegnæ s, S. S. R. Putluru, R. W.
Berg and A. Riisager, ChemCatChem, 2013, 5, 284.
33 J. Chen, Y. Guo, J. Chen, L. Song and L. Chen, ChemCatChem,
2014, , 3174.
34 F. Xu and Z. Zhang, ChemCatChem, 2015,
35 A. Takagaki, M.Takahashi, S. Nishimura and K. Ebitani, ACS
Catal., 2011, , 1562.
36 Z. Zhang, Z. Yuan, D. Tang, Y. Ren, K Lv and B. Liu,
ChemSusChem, 2014, , 3496.
6
7
, 1470.
1
7
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