Ruthenium complex immobilized on poly(4-vinylpyridine)-functionalized carbon-nanotube for selective aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

Article abstract of DOI:10.1039/c4ra14592e

Polymer/carbon composite material of poly(4-vinylpyridine)-functionalized carbon-nanotube (PVP/CNT) was prepared by in situ polymerization of 4-vinylpyridine monomer in the presence of CNT suspension. Raman spectra analysis confirmed the almost unchanged graphitized surfaces of CNT moiety in the PVP/CNT after the covalent functionalization of pristine CNT with PVP. Catalyst made of ruthenium complex immobilized on PVP/CNT (Ru-PVP/CNT) was fully characterized by ICP-OES, TG-DTA, FT-IR, Raman, XRD, UV-vis, BET, TEM, XPS and H₂-TPR. Moreover, Ru-PVP/CNT shows excellent catalytic performance towards the selective oxidation of biomass-based 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) with molecular oxygen as oxidant. The reaction parameters such as the reaction temperature, reaction time, solvent, catalyst amount, oxidant, and oxygen pressure were systematically investigated for this important biomass-related transformation. Under the optimal condition, a DFF yield of 94% with a full HMF conversion were obtained by using Ru-PVP/CNT in N,N-dimethylformamide (DMF) under 2.0 MPa O₂ at 120 °C. This journal is

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ARTICDLOIE: 10.10T39/YC4RPA145E92E
Ruthenium Complex Immobilized on Poly(4-vinylpyridine)-
Functionalized Carbon-Nanotube for Selective Aerobic Oxidation of 5-
Hydroxymethylfurfural to 2,5-Diformylfuran
Jinzhu Chen,*a Jiawei Zhong,a,c Yuanyuan Guoa and Limin Chenb
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Polymer-carbon composite material of poly(4-vinylpyridine)-functionalized carbon-nanotube (PVP/CNT)
was prepared by in situ polymerization of 4-vinylpyridine monomer in the presence of CNT suspension.
10 Raman spectra analysis confirmed the almost unchanged graphitized surfaces of CNT moiety in the
PVP/CNT after the covalent functionalization of pristine CNT with PVP. Catalyst made of ruthenium
complex immobilized on PVP/CNT (Ru-PVP/CNT) was fully characterized by ICP-OES, TG-DTA, FT-
IR, Raman, XRD, UV-vis, BET, TEM, XPS and H2-TPR. Moreover, Ru-PVP/CNT shows excellent
catalytic performance towards the selective oxidation of biomass-based 5-hydroxymethylfurfural (HMF)
15 to 2,5-diformylfuran (DFF) with molecular oxygen as oxidant. The reaction parameters such as the
reaction temperature, reaction time, solvent, catalyst amount, oxidant, and oxygen pressure were
systematically investigated for this important biomass-related transformation. Under the optimal
condition, a DFF yield of 94% with a full HMF conversion were obtained by using Ru-PVP/CNT in N,N-
dimethylformamide (DMF) under 2.0 MPa O2 at 120 °C.
(TEMPO).13-15 Nevertheless, the requirement of stoichiometric
oxidants and the release of hazardous wastes are unavoidable for
these methods. Therefore, selective oxidation of HMF to DFF
with environment friendly molecular oxygen as oxidant satisfied
the requirement of green chemistry.
1. Introduction
With the rapid depletion of fossil fuel and the aggravation of
global warming, much effort has been devoted to the production
of fuels and chemicals from renewable resources. As the only
carbon-containing renewable resource, biomass serves as an
alternative feedstock to provide fuels and chemicals.1, 2
5-Hydroxymethylfurfural (HMF), obtained from acid-promoted
dehydration of C6 based carbohydrate, has been identified as a
key platform chemical compound which can be transformed to a
4
variety of valuable chemicals and fuels.3, In particular, the
selective oxidation of HMF to 2,5-diformylfuran (DFF) has
attracted considerable interests in recent decades, due to the
applications of DFF in monomer, pharmaceuticals,5 fungicides,6
furan-urea resins7 as well as heterocyclic ligand.8 However, the
selective oxidation of HMF is influenced by various parameters
such as reaction temperature, reaction time, solvent, oxidants etc.
In addition, some byproducts such as 5-hydroxymethyl-2-
furancarboxylic acid (HMFCA), 5-formyl-2-furancarboxylic acid
(FFCA), 2,5-furandicarboxylic acid (FDCA) can be produced
during the process (Scheme 1). Therefore, it is still a challenging
task for the selective oxidation of HMF to DFF.
The selective oxidation of HMF to DFF have been reported by
using conventional oxidants such as NaOCl,9 BaMnO4,10
Pb(OAc)4-pyridine,11 K2Cr2O7-DMSO, trimethylammonium
chlorochromate (TMACC),12 oxalylchloride (OC), pyridinium
chlorochromate (PCC) and 2,2,6,6-tetramethylpiperidine-1-oxide
Scheme 1. Pathway of oxidation of HMF.
To date, homogeneous metal/bromide systems (Co/Mn/Br,
Co/Mn/Zr/Br)16 and heterogeneous transition metal-based
catalysts such as ruthenium,17-21 vanadium,22-31 manganese,9, 32, 33
copper23, 26 and silver34 have been developed for the production of
DFF from HMF or directly from carbohydrate.35-40 Recently, our
team achieved one-step approach to DFF directly from fructose
by using acidic cesium salts of molybdovanadophosphoric
heteropolyacids (CsMVP-HPAs)39 as well as proton- and
vanadium-containing graphitic carbon nitride [V-g-C3N4(H+)].40
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Among the developed catalyst systems, ruthenium-based catalyst
is proved to be more active and selective to this important
biomass-related transformation of HMF to DFF. For example,
series of nitrogen-containing polymer, including PVP- and
poly(1-vinylimidazole) (PVI)-functionalized CNT (Figure 1).
Moreover, the catalysts, made of palladiumDsOuIp: 1p0o.1rt0e3d9/oCn4RtAh1e4s5e92E
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Ebitani and coworkers obtained DFF from HMF with yield of 92% polymer/CNT composite materials, showed excellent selectivity
over hydrotalcite-supported ruthenium catalyst [Ru(OH)x/HT] in
N,N-dimethylformamide (DMF) using molecular oxygen as
oxidant.38 Antonyraj et al. achieved DFF from HMF with yield of
97% on RuCl3/Al2O3 at 130 °C with molecular oxygen.19 Zhang
and team members obtained DFF yield of 86.4% with
Fe3O4@SiO2-NH2-Ru(III) at 120 °C. It was found that Ru3+ ions
from RuCl3 aqueous solution can be effectively immobilized by
amino group of Fe3O4@SiO2-NH2.18 In addition, Corma et al.
obtained a DFF yield of 82% on immobilized vanadyl pyridine
complexes at 130 °C. It was observed that vanadyl groups can be
fully coordinated with pyridine ligand.29 Therefore, pyridine-
Ru(III) complex was investigated as catalyst for selective aerobic
oxidation of HMF to DFF in this research.
Currently, commercially available carbon materials such as
carbon nanotubes (CNT) have attracted ever-increasing attention
due to their high surface area, tunable surface properties, superior
mechanical strength etc. However, the lack of solubility and the
difficult manipulation of CNT in most solvents have limited their
use. Therefore, CNT generally needs to undergo chemical
functionalization to enhance solubility in various solvents and to
produce novel hybrid materials for practical applications.41 By
comparison, there is a large potential for the development and
application of organic polymer with tailored physical and
chemical properties in both selective catalysis and functional
material science, owing to the possibility of employing the vast
range of organic transformations developed by synthetic organic
chemists.42, 43 Therefore, to combine the advantages of polymer
and CNT, much effort has been put in polymer/CNT composite
material. For instance, our group recently developed poly(p-
styrenesulfonic acid)-functionalizd CNT (CNT-PSSA) as solid
acid for effective conversion of biomass-based fructose to HMF
and alkyl levulinate.44
towards hydrogenation of phenol and derivatives. Our research
results further indicate that the phenol conversion is related to the
conductive property of polymer/CNT; whereas, the
cyclohexanone selectivity is contributed to the nitrogen-
containing nature of polymer/CNT.42, 43
To explore the application of composite material PVP/CNT,
ruthenium complex was immobilized on the PVP/CNT (Ru-
PVP/CNT) through the formation of coordinative bond N:Ru3+
(Figure 2). Raman spectra analysis confirmed the almost
unchanged graphitized surfaces of CNT moieties in both
PVP/CNT and Ru-PVP/CNT after the functionalization of
pristine CNT. Moreover, the coordinative bond of N:Ru3+ in
Ru-PVP/CNT was confirmed by UV-vis and X-ray photoelectron
spectroscopy (XPS) analysis. The synthesized catalyst Ru-
PVP/CNT shows excellent catalytic performance towards the
selective oxidation of HMF to DFF with molecular oxygen as
oxidant (Scheme 1). Under the optimal condition, a DFF yield of
94% with full HMF conversion were obtained by using Ru-
PVP/CNT in DMF under 2.0 MPa O2 at 120 °C.
Fig. 2 Proposed structure of Ru-PVP/CNT.
2. Results and discussion
2.1 PVP/CNT and Ru-PVP/CNT
PVP/CNT composite material was prepared by polymerization of
4-vinylpyridine monomer with azobisisobutyronitrile (AIBN) as a
radical initiator in the presence of CNT suspension. According to
43, 52
literature,41,
the CNT is functionalized by poly(4-
vinylpyridine) through covalent chemical grafting in PVP/CNT.
The catalyst of Ru-PVP/CNT was synthesized by treating
PVP/CNT with aqueous solution of RuCl3, followed with
filtration and drying under vacuum. The inductively coupled
plasma-optical emission spectroscopy (ICP-OES) analysis of the
Ru-PVP/CNT showed that 2.2 wt% of Ru was immobilized on
PVP/CNT.
The thermal stabilities of CNT, PVP and PVP/CNT were
investigated by thermal gravimetric-differential thermal analysis
(TG-DTA). As shown in Figure 3, CNT shows no significant
weigh lose before 800 °C. By contrast, PVP shows the weight
loss of 2.4% at 100 °C, which is attributed to the loss of residual
moisture associated with PVP. In addition, PVP further shows
weight loss of 97.6% at 418 °C as supported with a sharp DTA at
Fig. 1 Proposed structure of PVP/CNT and PVI/CNT. (x indicates the
degree of polymerization).
In recent decades, transition metal complex with nitrogen-
containing polymer as ligand or immobilizer has attracted great
interests for catalysis purpose. Among the developed nitrogen-
containing polymers, due to the strong affinity of the pyridyl
group with transition metal ions, poly(4-vinylpyridine) (PVP)-
immobilized transition metal complexes45-47 have particularly
been used in various applications such as chemoselective
protection of aldehydes,48 selective solid phase extraction,49
hydrogenation and hydroformylation,50 water gas shift reaction,51
reduction of nitrobenzene.51 Recently, our team investigated a
2
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405 °C. As for PVP/CNT, beside the weight loss of 2.5% at
100 °C attributed to the loss of residual moisture, the main
decomposition started at 290 °C with the weight loss of 26.3%
which was supported by DTA at 330 °C. The similar TG-DTA
results were observed in Fullerene[60]-polyvinylpyridine
composites.53 TG-DTA of PVP/CNT thus confirmed that CNT
was successfully functionalized by polymer PVP.
moiety in the PVP/CNT composite.42, 43 Therefore, FT-IR results
further verify the existence of PVP chain segments in the as-
prepared PVP/CNT composite materials.
Raman spectroscopy is used to determine the changes of defect
density in the CNT moiety of PVP/CNT and Ru-PVP/CNT after
the polymerization and immobilization process (Figure 5). The
peak near 1576 cm−1 (G-band) corresponds to the E2g mode of
graphite. Whereas, the peak around 1342 cm−1 (D-band) is
associated with the vibrations of carbon atoms in the disordered
graphite structure, i.e., the defect sites. Generally, the intensity
ratio of the D-band to G-band (ID/IG) is used to determine the
defect density of CNT. The ID/IG is 0.85 for the pristine CNT and
then slightly increases to 0.88 for PVP/CNT and to 0.89 for Ru-
PVP/CNT. Therefore, Raman spectra analysis indicates that
graphitized surfaces of CNT moieties in both PVP/CNT and Ru-
PVP/CNT were almost unchanged after the covalent
functionalization of CNT with polymer PVP to give PVP/CNT
and the immobilization of Ru complex on PVP/CNT to afford
Ru-PVP/CNT, respectively.
a
100
80
60
CNT
PVP/CNT
PVP
40
20
0
200
400
600
Temperature /
CNT
PVP
0.5
0.4
0.3
0.2
0.1
0.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
b
CNT
PVP/CNT
PVP
PVP/CNT
2800
2400
Wavenumber / cm
2000
1600
-1
200
400
Temperature /
600
Fig. 4 FT-IR spectra of PVP and PVP/CNT.
Fig. 3 (a) TG and (b) DTA analysis of CNT, PVP, and PVP/CNT.
G
D
The Fourier transform infrared (FT-IR) spectra of PVP and
PVP/CNT are compared in Figure 4. As we have investigated
previously, the FT-IR spectrum of pristine CNT is practically
featureless with extremely low infrared absorption intensities.42, 44
For PVP/CNT, the IR bands at 2919 and 2850 cm−1 were
assigned to asymmetric and symmetric vibration absorptions,
respectively, for C–H band of the aliphatic CH2 in vinyl chain. In
the case of PVP, the corresponding bands are observed at 2926
and 2854 cm−1, respectively. In addition, the absorption bands of
PVP/CNT around 1580 cm-1 are assigned to the C=C stretching
vibration of pyridine ring. The absorption bands at 1462 and 1441
cm-1 are attributed to C=N stretching vibration of pyridine ring in
PVP/CNT, which are in accordance with the reported
observance.54 The spectrum shifts between PVP and PVP/CNT
are attributed to the strong π-π interaction between PVP and CNT
CNT
PVP/CNT
Ru-PVP/CNT
1000
1500
2000
-1
Raman Shift / cm
Fig. 5 Raman spectra of CNT, PVP/CNT and Ru-PVP/CNT.
The Ultraviolet visible (UV-vis) spectra of PVP/CNT and Ru-
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PVP/CNT are compared in Figure S1 (ESI). For PVP/CNT, the
bands at 207 and 255 nm are attributed to the absorptions of
π→π* and n→π* orbits of PVP, respectively. In the case of Ru-
PVP/CNT, the corresponding absorption band shift to 210 and
258 nm, respectively. Therefore, the presence of Ru3+ ions in Ru-
PVP/CNT lead to red shifts of PVP/CNT in both bands, which is
attributed to the formation of coordination bonds between pyridyl
ligand in PVP and Ru3+ ions in the Ru-PVP/CNT.
The surface morphologies of the CNT and PVP/CNT were
further observed by transmission electron microscopy (TEM).
The outside diameter of pristine CNT falls into the raVgieewoAfrt1ic0le Otonline
DOI: 10.1039/C4RA14592E
20 nm with the CNT length around 10~30 um (Figure S3, ESI).
In contrast, PVP/CNT shows a thin polymer coating of 2-4 nm
over CNT (Figure 7). Thus, TEM analysis of PVP/CNT
effectively confirmed the functionalization of CNT with polymer
PVP.
The Brunauer-Emmett-Teller (BET) surface areas and the pore
sizes of PVP/CNT and Ru-PVP/CNT were calculated with BET
and Barrett-Joyner-Halenda (BJH) methods. As determined from
the nitrogen adsorption/desorption isotherm in Figure S2 (ESI),
the average pore diameter and total pore volume for PVP/CNT
are 16.5 nm and 0.35 cm3 g-1, respectively. By comparison, the
average pore diameter and total pore volume for Ru-PVP/CNT
decrease to 14.6 nm and 0.33 cm3 g-1, respectively. However,
BET surface areas of PVP/CNT and Ru-PVP/CNT are 84.8 and
89.4 m2 g-1. The slightly increased surface area can be attributed
to the formation of new pore in the matrix of PVP/CNT.42
The Powder X-ray diffraction (XRD) patterns of PVP/CNT and
Ru-PVP/CNT show no distinct difference (Figure 6), though a
slight attenuation of the diffraction peaks at 26, indicating that
the immobilization process does not greatly damage the
crystallinity structure of PVP/CNT. The diffraction peaks of both
PVP/CNT and Ru-PVP/CNT located at a 2 value of about 26
and 43 were assigned to the characteristic peaks of the (002) and
(100) packing of graphitic CNT, respectively.42, 43 Moreover, the
distinct reflections for Ru(0) and RuO2 were unobserved in XRD
results,55 which proves the unchanged valence state of Ru(III)
during the catalyst preparation process.18, 55
The surface composition of PVP/CNT and Ru-PVP/CNT were
investigated with X-ray photoelectron spectroscopy (XPS).
Peaks corresponding to carbon, oxygen, nitrogen, ruthenium and
chlorine are presented in the survey scan (Figure 8a).
Corresponding O1s signals were possibly arose from surface
impurities.56 For Ru-PVP/CNT, there is an overlap between Ru
56
3d and C 1s peak at around 282.5 eV.18,
The presence of
chlorine peak indicated that Cl− ion acts as the counter ion of
Ru3+ ion.45 The binding energy at 461.8 and 484.2 eV are
assigned to Ru 3p3/2 and Ru 3p1/2, respectively, which
demonstrates that the oxidation state of the ruthenium species is
Ru3+ (Figure 8b).18, 57 The N 1s binding energies are 397.0 and
397.4 eV for PVP/CNT and Ru-PVP/CNT, respectively (Figure
8c). The observed shift in N 1s binding energies indicates that
coordination bonds are presumably formed between nitrogen
atom of pyridyl ligand and Ru3+ ion in Ru-PVP/CNT.
a
C1s
N1s
O1s
O1s
PVP/CNT
C1s+Ru3d
Cl 2p
(002)
Ru3p
N1s
400
Ru-PVP/CNT
600
500
300
200
100 0
(100)
Binding Energy / eV
(002)
PVP-CNT
(100)
b
Ru-PVP-CNT
Ru3p
3/2
Ru3p
1/2
20
40
60
80
2 theta / degree
Fig. 6 XRD patterns of PVP/CNT and Ru-PVP/CNT.
490
480
470
460
450
Binding Energy / eV
Fig. 7 TEM images of PVP/CNT.
4
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c
100 oC
110 oC
120 oC
HMF Conv.
HMF Conv.
HMF Conv.
DFF Yield
DFF Yield
DFF Yield
397.0
N 1s
100
100
80
60
40
20
0
PVP/CNT
80
60
40
20
0
397.4
Ru-PVP/CNT
400
398
396
394
Binding energy / eV
0
2
4
6
8
10
12
Fig. 8 (a) XPS scan survey for PVP/CNT and Ru-PVP/CNT, (b) Ru 3p
XPS spectra of Ru-PVP/CNT, (c) N 1s XPS spectra of PVP/CNT and Ru-
PVP/CNT.
Time / h
Fig. 9 The influences of reaction temperature and time on the aerobic
oxidation of HMF to DFF. Reaction conditions: HMF (63 mg, 0.5 mmol),
Ru-PVP/CNT (60 mg, Ru 2.2 wt%), DMF (5 mL), O2 (2.0 MPa).
The Temperature-programmed reduction (H2-TPR) profile for
Ru-PVP/CNT is provided in Figure S4 (ESI). Two reduction
peaks take place around 173 and 540 °C for Ru-PVP/CNT, the
peak at 173 °C results from the reduction of Ru complex;
whereas, hydrogen consumption observed at 540 °C is attributed
to the methanation of PVP/CNT.58 Therefore, the H2-TPR profile
effectively testifies that Ru species is in the form of Ru3+ rather
than Ru0 in Ru-PVP/CNT.
It is widely accepted that the nature of solvent have great
impacts on the conversion rate of HMF and selectivity to DFF.
Therefore, various solvents such as high boiling and polar
solvents [DMF and dimethylsulfoxide (DMSO)], low boiling and
polar solvents [isopropyl alcohol (IPA), ethanol (EtOH),
acetonitrile (MeCN), 1,4-dioxane and water] and non-polar
solvent (toluene) are investigated so as to study the solvent effect
on the aerobic oxidation of HMF. Among all the solvents tested,
DMF showed HMF conversion of >99% with DFF selectivity of
95% (Table 1, Entry 1), which may be ascribed to the high
solubility of oxygen in DMF.34 Satisfying result can also be
achieved with the use of toluene (Table 1, Entry 2).19, 20 1,4-
dioxane and water achieved high HMF conversion but low DFF
selectivity (Table 1, Entries 4-5), which may be attributed to the
decomposition of 1,4-dioxane molecule19 and the hydration of the
2.2 Selective aerobic oxidation of HMF over Ru-PVP/CNT
The prepared Ru-PVP/CNT was investigated as potential catalyst
for selective aerobic oxidation of HMF to DFF. The reaction is
typically carried out in DMF under 2.0 MPa O2. Figure 9 shows
the effects of reaction temperature and time on the aerobic
oxidation of HMF to DFF. Both the HMF conversion and DFF
yield increased with reaction time at all temperatures investigated.
The yield of DFF increased slowly to 67% after 12 h at 100 °C;
whereas, it increased quickly to 94% after 12 h at 120 °C,
confirming that increasing the reaction temperature promotes the
aerobic oxidation of HMF to DFF. The result was consistent with
the previous reports.17-19, 32, 34
aldehyde groups in HMF and DFF to germinal diols,21,
59
respectively. Alcohol-type solvents (IPA and EtOH) also
achieved great HMF conversion and selectivity toward DFF
(Table 1, Entries 3, 6).19 MeCN and DMSO attained modest level
of HMF conversion (Table 1, Entries 7-8), the poor performance
of DMSO may be ascribed to the strong coordination effect of
60
DMSO molecule with Ru3+ center.20,
Besides, it has been
reported that DMSO tend to undergo disproportionation to yield
toxic Me2SO2 and Me2S under oxidizing conditions.21
Table 1 Effect of solvents on the aerobic oxidation of HMF to DFFa
Entry Solvent
HMF
conversion
(%)
DFF
yield
(%)
94
DFF
selectivity
(%)
1
2
N,N-dimethylformamide
Toluene
>99
>99
95
88
87
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3
4
5
6
7
8
Isopropyl alcohol
1,4-Dioxane
Water
Ethanol
Acetonitrile
Dimethylsulfoxide
>99
>99
>99
92
70
60
77
35
13
83
66
52
78
35
13
89
94
86
2, Entry 5), which can be attributed to the strong oxidative
capability of t-BuOOH leading to the breakage of the furan
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ring.17, 18 By contrast, low HMF conversion of 47% and low DFF
DOI: 10.1039/C4RA14592E
yield of 32% were obtained by using H2O2 (Table 2, Entry 6),
which is presumably attributed to the quick decomposition of
H2O2 catalyzed by ruthenium species.17, 61 Therefore, the mild
oxidant H2O2 was not effective for the oxidation of HMF to DFF,
which is consistent with the previous results.18, 32
a Reaction conditions: HMF (63 mg, 0.5 mmol), Ru-PVP/CNT (60 mg, Ru
2.2 wt%), solvent (5 mL), O2 (2.0 MPa), 120 °C, 12 h.
Table 2 Catalytic oxidation of HMF using various oxidantsa
HMF Conv.
DFF Yield
DFF Sel.
100
80
60
40
20
0
100
80
60
40
20
0
Entry Oxidant
HMF conversion DFF yield
DFF selectivity
(%)
>99
95
83
26
(%)
94
90
80
25
13
32
(%)
95
95
96
96
13
68
b
1
2
3
4
5
6
O2
O2
O2
O2
c
d
e
t-BuOOH f
H2O2
98
47
g
a Reaction conditions: HMF (63 mg, 0.5 mmol), Ru-PVP/CNT (60 mg, Ru
2.2 wt%), DMF (5 mL), 120 °C, 12 h. b O2 (2.0 MPa), c O2 (1.0 MPa), d O2
(0.5 MPa), e O2 (0.1 MPa), f t-BuOOH (3.5 mmol), g H2O2 (3.5 mmol)
were used, respectively.
40
50
Catalyst amount / mg
60
Fig. 10 Aerobic oxidation of HMF to DFF with various catalyst dosages.
Reaction conditions: HMF (63 mg, 0.5 mmol), Ru-PVP/CNT (Ru 2.2
wt%), DMF (5 mL), O2 (2.0 MPa), 120 °C, 12 h.
100
80
60
40
20
0
100
80
60
40
20
0
HMF Conv.
DFF Yield
In addition to the solvent effect, the catalyst Ru-PVP/CNT
loading level also exhibits a dramatic influence on the aerobic
oxidation of HMF to DFF. As shown in Figure 10, HMF
conversions of 82% and 95% were obtained after 12 h with 40
mg and 50 mg of Ru-PVP/CNT, respectively, the corresponding
DFF yields were 77% and 88%. Notably, HMF conversion and
DFF yield increased to >99% and 94%, respectively, after 12 h
by the use of 60 mg of Ru-PVP/CNT. The higher the catalyst
loading, the higher both HMF conversion and DFF yield. The
results indicate that the increase of the catalyst amount leads to
the increase of the aerobic oxidation rate of HMF to DFF, which
should be ascribed to the increase in the number and availability
of catalytically active sites.34 Notably, the selectivity of DFF
almost always maintained around 92-95% regardless of catalyst
loading level (Figure 10). This result suggests that the use of Ru-
PVP/CNT can effectively avoid further oxidation of DFF to
FFCA under the investigated conditions, thus leading to a high
selectivity to DFF. In fact, the DFF selectivity is mainly
determined by the reaction temperature, the solvent as well as the
oxidant in this research.17, 18, 32
In general, oxidant plays a vital role on the conversion rate of
HMF and selectivity to DFF. As shown in Table 2, molecular
oxygen, the clean and easily available oxidant, was most effective
for the oxidation of HMF to DFF. An increase of the oxygen
pressure leads to an increase of both HMF conversion and DFF
yield (Table 2, Entries 1-4), which is ascribed to an enhanced
molecular oxygen concentration in the solvent with the increase
of oxygen pressure.20, 34 In addition to O2, common oxidants such
as tert-butyl hydroperoxide (t-BuOOH) and hydrogen peroxide
(H2O2) were also explored for the oxidation of HMF to DFF.
However, DFF yield was rather low with t-BuOOH as the oxidant
though nearly quantitative HMF conversion was observed (Table
Fig. 11 Aerobic oxidation of HMF to DFF with various catalysts.
Reaction conditions: HMF (63 mg, 0.5 mmol), catalyst (60 mg), DMF (5
mL), O2 (2.0 MPa), 120 °C, 12 h.
In addition to Ru-PVP/CNT, various other ruthenium catalysts,
made of Ru3+ immobilized on PVP and PVI/CNT (Figure 1),
were further investigated to probe the influence of support on the
selective aerobic oxidation of HMF to DFF (Figure 11). Without
immobilization of Ru3+, no oxidation products were detected with
the use of pristine PVP/CNT in the blank experiment (Figure 11),
which indicated that the Ru rather than the support PVP/CNT
showed catalytic activity in the aerobic oxidation of HMF.19 In
the case of Ru-PVP and Ru-PVI/CNT, moderate HMF
conversions and DFF yields were observed. Obviously, among all
the catalysts explored, Ru-PVP/CNT is considerably more active
and selective to afford DFF from HMF under the investigated
conditions, presumably owing to the strong coordination ability
of the pyridyl ligand to the ruthenium ion in the Ru-PVP/CNT.
The decrease in HMF conversion with recycled Ru-PVP/CNT
may be attributed to the leaching of active metal (ICP-OES
6
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analysis of the recycled Ru-PVP/CNT showed that 1.9 wt% of Ru
was immobilized on PVP/CNT), the inevitable losses of catalyst
during filtration18 and the insoluble polymeric furanic compounds
adsorbed on the catalyst19.
time at 120 °C under 2.0 MPa O2. After the reaction, the mixture
was cooled to ambient temperature. The quantitative analysis
methods of substrate and product are provided in the Supporting
Information.
Reusability of the catalyst
3. Conclusions
The resulting precipitates were filtrated from the reaction mixture
by nylon membrane and washed with de-ionized water. The solid
powder was then dried in a vacuum oven at 60 C until it attained
constant weight. The recovered catalyst was used for the next
circle, and other steps were the same as those described above.
In conclusion, the composite material of poly(4-vinylpyridine)-
functionalized carbon-nanotube (PVP/CNT) was prepared by in
situ polymerization of 4-vinylpyridine monomer in the presence
of CNT suspension. Raman spectra analysis confirmed the almost
unchanged graphitized surfaces of CNT moiety in the PVP/CNT
after the covalent functionalization of pristine CNT with PVP.
The catalyst of ruthenium complex immobilized on PVP/CNT
(Ru-PVP/CNT) shows excellent catalytic performance towards
5. Acknowledgements
We are grateful for the financial support from National Natural
Science Foundation of China (21472189, 21172219, 51406211
and 21207039), National Basic Research Program of China (973
Program, 2012CB215304), 100 Talents Program of the Chinese
Academy of Sciences, and Guangdong Natural Science
selective
aerobic
oxidation
of
biomass-based
5-
hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF).
Under the optimal condition, a DFF yield of 94% with a full
HMF conversion were obtained by using Ru-PVP/CNT in N,N-
dimethylformamide (DMF) under 2.0 MPa O2 after 12 h at
120 °C. The research highlights a good prospect for catalytic
application of polymer-CNT composite material for biomass-
related transformations.
Foundation
(S2013010012986,
S2011010000737
and
S2013040012615).
Notes and references
a
CAS Key Laboratory of Renewable Energy, Guangzhou Institute of
Energy Conversion, Chinese Academy of Sciences. Guangzhou 510640
(PR China). E-mail: chenjz@ms.giec.ac.cn. Tel./Fax: +86-20-3722-3380.
4. Experiment
b
College of Environment and Energy, South China University of
Materials and Characterization
Technology, Guangzhou 510006 (PR China)
c University of Chinese Academy of Sciences. Beijing 100049 (PR China).
† Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
Materials and catalyst characterizations are provided in the
Supporting Information.
Catalyst Preparation
1. P. Gallezot, Chem. Soc. Rev., 2012, 41, 1538-1558.
2. J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew. Chem. Int. Ed,
2007, 46, 7164-7183.
3. R. J. V. Putten, J. C. V. D. Waal, E. D. Jong, C. B. Rasrendra, H. J.
Heeres and J. G. D. Vries, Chem. Rew., 2013, 113, 1499-1597.
4. A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and C. A. M. Afonso,
Green Chem., 2011, 13, 754-793
5. K. T. Hopkins, W. D. Wilson, B. C. Bender, D. R. McCurdy, J. E.
Hall, R. R. Tidwell, A. Kumar, M. Bajic and D. W. Boykin, J. Med.E
Chem., 1998, 41, 3872-3878.
6. M. D. Poeta, W. A. Schell, C. C. Dykstra, S. Jones, R. R. Tidwell, A.
Czarny, M. Bajic, A. Kumar, D. Boykin and J. R. Perfect, Antimicrob.
Agents Ch., 1998, 42, 2495-2502.
Preparation of polymer/CNT and polymer: The polymer/CNT
was prepared by the polymerization of the corresponding polymer
52
monomer in the presence of CNT. The PVP/CNT,43,
62
52
PVI/CNT42,
and PVP43,
were prepared according to the
published literature and the corresponding synthetic procedures
were provided in the supporting Information.
Preparation of Ru-PVP/CNT: PVP/CNT (60 mg) was added to
an aqueous ruthenium chloride solution (20 mL, 5 ×10−3 mol L-1).
The mixture was stirred for 12 h at room temperature. The
resulting precipitates were filtrated and washed with de-ionized
water twice to remove adsorbed and uncomplexed metal salt.
Then the solid powder was dried in a vacuum oven at 60 C until
it attained constant weigh. Ru-PVI/CNT and Ru-PVP were
prepared following the same procedures.
7. A. S. Amarasekara, D. Green and L. D. Williams, Eur. Polym. J.,
2009, 45, 595-598.
8. D. T. Richter and T. D. Lash, Tetrahedron Lett., 1999, 40, 6735-6738.
9. A. S. Amarasekara, D. Green and E. McMillan, Catal. Commun.,
2008, 9, 286-288.
Typical Procedures for the Aerobic Oxidation of HMF to
DFF.
10. T. E. Hajj, J. C. Martin and G. Descotes, J. Heterocyclic Chem., 1983,
20, 233-235.
11. J. W. V. Reijendam, G. J. Heeres and M. J. Janssen, Tetrahedron,
1970, 26, 1291-1301.
12. L. Cottier, G. Descotes, J. Lewkowski and R. Skowroñski, Org. Prep.
Proced. Int., 1995, 27, 564-566.
13. L. Cottier, G. Descotes, E. Viollet, J. Lewkowski and R. Skowroñski,
J. Heterocyclic Chem., 1995, 32, 927-930.
Aerobic oxidation of HMF was carried out in Teflon-lined
stainless steel autoclave (50 mL). Typically, HMF (63 mg, 0.5
mmol) and Ru-PVP/CNT (60 mg, Ru 2.2 wt%) was added into
DMF (5 mL), and the mixtures were stirred at ca. 700 rpm during
the reactions. The reaction was carried out at a given reaction
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ARTICLE TYPE
14. B. Karimi, H. M. Mirzaei and E. Farhangi, ChemCatChem, 2014, 6,
758-762.
39. R. L. Liu, J. Z. Chen, L. M. Chen, Y. Y. Guo and J. W. Zhong,
ChemPlusChem, 2014, 79, 1448–1454
15. N. Mittal, G. M. Nisola, L. B. Malihan, J. G. Seo, S. P. Lee and W. J.
Chung, Korean J. Chem. Eng., 2014, 31, 1362-1367.
16. W. Partenheimer and V. V. Grushin, Adv. Synth. Catal., 2001, 343,
102-111.
17. Y. Wang, B. Liu, K. C. Huang and Z. H. Zhang, Ind. Eng. Chem.
Res., 2014, 53, 1313-1319.
40. J. Z. Chen, Y. Y. Guo, J. Y. Chen, L. Song and L. M. Chen,
View Article Online
DOI: 10.1039/C4RA14592E
ChemCatChem, 2014, 6, 3174–3181.
41. N. Karousis and N. Tagmatarchis, Chem. Rev. 2010, 110, 5366–5397.
42. J. Z. Chen, W. Zhang, L. M. Chen, L. L. Ma, H. Gao and T. J. Wang,
ChemPlusChem, 2013, 78, 142-148.
43. A. B. Chen, Y. L. Li, J. Z. Chen, G. Y. Zhao, L. L. Ma and Y. F. Yu,
ChemPlusChem, 2013, 78, 1370-1378.
44. R. L. Liu, J. Z. Chen, X. Huang, L. M. Chen, L. L. Ma and X. J. Li,
Green Chem., 2013, 15, 2895-2903.
45. J. M. Clear, J. M. Kelly and J. G. Vos, Macromol. Chem. Phys., 1993,
184, 613-625.
46. N. H. Agnew, J. Polym. Sci. Polym. Chem. Ed., 1976, 14, 2819-2830.
47. L. A. Belfiore, M. P. McCurdie and E. Ueda, Macromolecules, 1993,
26, 6908-6917.
48. S. W. Kshirsagar, N. R. Patil and S. D. Samant, Synthetic Commun.,
2010, 40, 407-413.
49. P. Mondal, S. P. Bayen, K. Roy and P. Chowdhury, Sep. Sci.
Technol., 2012, 47, 1651-1659.
50. M. M. Mdleleni, R. G. Rinker and P. C. Ford, Inorg.Chim. Acta,
1998, 270, 345-352.
18. S. G. Wang, Z. H. Zhang, B. Liu and J. L. Li, Ind. Eng. Chem. Res.,
2014, 53, 5820-5827.
19. C. A. Antonyraj, J. Jeong, B. Kim, S. Shin, S. Kim, K. Y. Lee and J.
K. Cho, J. Ind. Eng. Chem., 2013, 19, 1056-1059.
20. J. F. Nie, J. H. Xie and H. C. Liu, J. Catal., 2013, 301, 83-91.
21. J. F. Nie, J. H. Xie and H. C. Liu, Chinese J. Catal., 2013, 34, 871-
875.
22. I. Sádaba, Y. Y. Gorbanev, S. Kegnaes, S. S. R. Putluru, R. W. Berg
and A. Riisager, ChemCatChem, 2013, 5, 284-293.
23. N. T. Le, P. Lakshmanan, K. Cho, Y. Han and H. Kim, Appl. Catal.,
A, 2013, 464-465, 305-312.
24. F. L. Grasset, B. Katryniok, S. Paul, V. Nardello-Rataj, M. Pera-Titus,
J. M. Clacens, F. D. Campo and F. Dumeignil, RSC Adv., 2013, 3,
9942-9948.
25. J. F. Nie and H. C. Liu, Pure Appl. Chem., 2012, 84, 765-777.
26. J. P. Ma, Z. T. Du, J. Xu, Q. H. Chu and Y. Pang, ChemSusChem,
2011, 4, 51-54.
51. A. J. Pardey, A. D. Rojas, J. E. Yánez, P. Betancourt, C. Scott,
CarlosChinea, C. Urbina, D. Moronta and C. Longo, Polyhedron,
2005, 24, 511-519.
27. C. Carlini, P. Patrono, A. M. R. Galletti, G. Sbrana and V. Zima,
Appl. Catal., A, 2005, 289, 197-204.
52. S. H. Qin, D. Q. Qin, W. T. Ford, J. E. Herrera and D. E. Resasco,
Macromolecules, 2004, 37, 9963-9967.
28. C. Moreau, R. Durand, C. Pourcheron and D. Tichit, Stud. Surf. Sci.
Catal. 1997, 108, 399-406.
53. M. G. H. Zaidi, T. Agarwal, S. Alam and A. K. Rai, Fuller. Nanotub.
Car. N., 2011, 19, 329-342.
29. O. C. Navarro, A. C. Canós and S. I. Chornet, Top.Catal., 2009, 52,
304-314.
30. X. Q. Jia, J. P. Ma, M. Wang, Z. T. Du, F. Lu, F. Wang and J. Xu,
Appl. Catal., A, 2014, 482, 231-236.
31. C. A. Antonyraj, B. Kim, Y. Kim, S. Shin, K. Y. Lee, I. Kim and J. K.
Cho, Catal. Commun., 2014, 57, 64-68.
32. B. Liu, Z. H. Zhang, K. L. Lv, K. J. Deng and H. M. Duan, Appl.
Catal., A, 2014, 472, 64-71.
33. J. F. Nie and H. C. Liu, J. Catal., 2014, 316, 57-66.
34. G. D. Yadav and R. V. Sharma, Appl. Catal., B, 2014, 147, 293-301.
35. G. A. Halliday, R. J. Young and V. V. Grushin, Org. Lett., 2003, 5,
2003-2005.
36. X. Xiang, L. He, Y. Yang, B. Guo, D. M. Tong and C. W. Hu, Catal.
Lett., 2011, 141, 735-741.
37. H. J. Yoon, J. W. Choi, H. S. Jang, J. K. Cho, J.W. Byun, W. J.
Chung, S. M. Lee and Y. S. Lee, Synlett, 2011, 165-168.
38. A. Takagaki, M. Takahashi, S. Nishimura and K. Ebitani, ACS Catal.,
2011, 1, 1562-1565.
54. H. B. Friedrich and N. Singh, Catal. Lett., 2006, 110, 61-70.G. P.
Rachiero, U. B. Demirci and P. Miele, Catal. Today, 2011, 170, 85-
92.
55. H. Y. H. Chan, C. C. Takoudis and M. J. Weaver, J. Catal., 1997,
172, 336-345.
56. G. P. Williams, CRC Handbook of Chemistry and Physics, CRC
Press: Boca Raton, 2001, pp. 200.
57. T. Komanoya, H. Kobayashi, K. Hara, W. J. Chun and A. Fukuoka,
Appl. Catal., A, 2011, 407, 188-194.
58. S. E. Davis, B. N. Zope and R. J. Davis, Green Chem., 2012, 14, 143-
147.
59. K. Mori, T. Hara, T. Mizugaki, K. Ebitani and K. Kaneda, J. Am.
Chem. Soc, 2004, 126, 10657–10666.
60. P. C. Selvaraj and V. Mahadevan, J. Mol. Catal. A: Chem., 1997, 120,
47-54.
61. M. Takafuji, S. Ide, H. Ihara and Z. H. Xu, Chem. Mater., 2004, 16,
1977-1983.
TOC
Ruthenium complex, immobilized on poly(4-vinylpyridine)-functionalized carbon-nanotube, shows excellent catalytic performance
towards selective aerobic oxidation of biomass-based 5-hydroxymethylfurfural to 2,5-diformylfuran.
8
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