Alkaline ionic liquid modified Pd/C catalyst as an efficient catalyst for oxidation of 5-hydroxymethylfurfural

Article abstract of DOI:10.1155/2018/2018743

Conversion of HMF into FDCA was carried out by a simple and green process based on alkaline ionic liquid (IL) modified Pd/C catalyst (Pd/C-OH^-). Alkaline ionic liquids were chosen to optimize Pd/C catalyst for special hydrophilicity and hydrophobicity, redox stability, and unique dissolving abilities for polar compounds. The Pd/C-OH^- catalyst was successfully prepared and characterized by SEM, XRD, TG, FT-IR, and CO₂-TPD technologies. Loading of alkaline ionic liquid on the surface of Pd/C was 2.54 mmol·g^-1. The catalyst showed excellent catalytic activity in the HMF oxidation after optimization of reaction temperature, reaction time, catalyst amount, and solvent. Supported alkaline ionic liquid (IL) could be a substitute and promotion for homogeneous base (NaOH). Under optimal reaction conditions, high HMF conversion of 100% and FDCA yield of 82.39% were achieved over Pd/C-OH^- catalyst in water at 373 K for 24 h.

Full text of DOI:10.1155/2018/2018743

Hindawi
Journal of Chemistry
Volume 2018, Article ID 2018743, 9 pages
https://doi.org/10.1155/2018/2018743
Research Article
Alkaline Ionic Liquid Modified Pd/C Catalyst as an Efficient
Catalyst for Oxidation of 5-Hydroxymethylfurfural
Zou Bin , Chen Xueshan, Xia Jiaojiao, and Zhou Cunshan
School of Food and Biological Engineering, Jiangsu University, Zhenjiang 212013, China
Correspondence should be addressed to Zou Bin; binzou2009@ujs.edu.cn
Received 27 October 2017; Accepted 13 February 2018; Published 2 April 2018
Academic Editor: Bartolo Gabriele
Copyright © 2018 Zou Bin et al. Tis is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Conversion of HMF into FDCA was carried out by a simple and green process based on alkaline ionic liquid (IL) modifed Pd/C
catalyst (Pd/C-OH−). Alkaline ionic liquids were chosen to optimize Pd/C catalyst for special hydrophilicity and hydrophobicity,
redox stability, and unique dissolving abilities for polar compounds. Te Pd/C-OH− catalyst was successfully prepared and
characterized by SEM, XRD, TG, FT-IR, and CO -TPD technologies. Loading of alkaline ionic liquid on the surface of Pd/C was
2
2.54 mmol⋅g−1. Te catalyst showed excellent catalytic activity in the HMF oxidation afer optimization of reaction temperature,
reaction time, catalyst amount, and solvent. Supported alkaline ionic liquid (IL) could be a substitute and promotion for
homogeneous base (NaOH). Under optimal reaction conditions, high HMF conversion of 100% and FDCA yield of 82.39% were
achieved over Pd/C-OH− catalyst in water at 373 K for 24 h.
1. Introduction
the most important chemical building blocks from HMF via
oxidation, can be used as a substitute for purifed terephthalic
acid (PTA) to produce bulk polyester materials, because it has
a similar structure and properties with PTA [13, 14]; therefore,
it is of great market potential to study the process of catalytic
oxidation of HMF.
Currently, fuel and chemicals needed in society are largely
derived from fossil fuels. Rapid depletion of fossil resources
has generated widespread interest in the utilization of renew-
able resources for the sustainable production of fuel and
chemicals. Renewable energy, such as wind energy, solar
energy, and geothermal energy, cannot be used to produce
organic chemicals that are currently based on fossil fuels.
In contrast, biomass resources with a large proportion of
carbohydrates are extensive. Trough selective dehydration
or hydrogenation processes, biomass can produce liquid
fuels and organic chemicals [1–3]. 5-Hydroxymethylfurfural
(HMF) is one of the important biomass-based platform com-
pounds [4, 5]. It can be obtained by catalyzing the dehydra-
tion of carbohydrates such as fructose, glucose, and cellulose
[6–8]. HMF can be used to prepare important monomers
of fne chemicals and polymers by oxidation, hydrogenation,
ring opening, and polymerization [9]. Products can be used
in medicine, plastics, fuel, and other felds. Te study on
the synthesis of important organic chemical intermediates
or products from HMF as a platform has attracted immense
attention [10–12]. 2,5-Furandicarboxylic acid (FDCA), one of
In the process of producing FDCA, frst of all, Miura et
al. used traditional oxidant KMnO to synthesize FDCA [15].
4
Te method has high cost and low catalytic selectivity. Also,
homogeneous metal catalyst (Co2+/Mn2+/Br−) was used for
aqueous HMF oxidation [16]. But the catalyst could not be
reused. Due to the difculty of separation and poor reuse of
the homogeneous catalysts, it is preferred to utilize heteroge-
neous catalysts over homogeneous catalysts for the oxidation
of HMF into FDCA. Current literatures have reported using
a variety of supported catalysts involving expensive precious
metals with higher catalytic efciency for the preparation of
FDCA [17–19].
Among Pd, Pt, Ru, and Au-based catalysts, the catalytic
efciency of supported Pd nanoparticles is remarkable [20].
Active carbon materials have many excellent properties in
support materials. Tey have good stability in high tempera-
ture, high pressure, acid, alkaline solution, and other reaction

2
Journal of Chemistry
O
O
Pd/C-／（−
O
O
HO
HO
OH
H
Base, oxygen
HFCA
Pd/C-／（−
Base, oxygen
O
O
O
O
O
O
Pd/C-／（−
OH
HO
OH
H
Base, oxygen
FDCA
FFCA
Scheme 1: Reaction of HMF oxidation to FDCA.
conditions. More importantly, their surface has abundant
functional groups, which can be used to adsorb metal ions
and immobilized metal nanoparticles [21, 22]. Terefore
Pd loaded on activated carbon (Pd/C) has high catalytic
activity in theory. Davis et al. have reported a 71% yield of
FDCA over Pd/C under 690 kPa oxygen pressure and 295 K
[23].
the optimal conditions without addition of homogeneous
base.
2. Experimental Section
2.1. Materials. 5-Hydroxymethyl-2-furancarboxylic acid
(HFCA), 5-formyl-2-furancarboxylic acid (FFCA), HMF,
and FDCA were purchased from the J&K Chemical Co.,
Te oxidation of HMF requires addition of homogeneous
base while utilizing noble metal-based catalysts. Without
base, FDCA may not be produced in large quantities. It is
now pointed out that the base can remove the HMF acidic
oxidation product accumulated on the catalyst surface and
allow the reaction to proceed continuously. For example, Nie
et al. demonstrated a base-free process for no FDCA synthesis
using activated carbon loaded Ru metal nanoparticles (Ru/C)
catalyst in toluene with 95.8% 2,5-diformylfuran (DFF) yield
[24]. But adding a large amount of base in the reaction system
will increase the cost and pollute the environment. Terefore,
some scholars consider the preparation of solid base as the
catalyst carrier, For example, Wan et al. loaded bimetallic Au
and Pd onto solid base carrier hydrotalcite (HT) to catalyze
the oxidation of HMF. Without adding homogeneous base,
fnally, the reaction achieved a high yield of FDCA [25].
Although solid base HT can be used as a potential alternative
to homogeneous base, it still has some problems. Zope et al.
have investigated that the Mg2+ component leaching from
the HT reacted with the product acid during reaction [26].
Te interaction between solid base material and product must
be considered.
In this work, we report a much more environmentally
benign and safe process for aqueous HMF oxidation using
solid base modifed activated carbon-supported palladium
nanoparticle catalyst (Pd/C-OH−). Conversion of HMF into
FDCA could be carried out by a simple and green process
based on a novel ionic liquid (IL) modifed Pd/C catalyst and
then exchanged Cl− in ionic liquid with OH− (Scheme 1).
Alkaline ionic liquids were chosen to optimize Pd/C cat-
alyst for their special hydrophilicity and hydrophobicity,
redox stability, and unique dissolving abilities for polar
compounds [27]. Finally, Pd/C-OH− catalyst was found
to exhibit remarkable activity for FDCA synthesis under
Ltd. (Shanghai, China). Palladium(II) chloride (PdCl ,
2
59% Pd) was purchased from Aladdin Chemicals Co.,
Ltd. (Beijing, China). Activated carbon was purchased
from Sigma-Aldrich (Beijing, China). 1-Methylimidazole, 3-
(Chloropropyl)triethoxysilane, and all solvents were pur-
chased from Sinopharm Chemical Reagents (Shanghai,
China).
2.2. Preparation of Pd/C Catalyst. Pd/C was prepared by
incipient wetness impregnation of activated carbon with
aqueous solution of PdCl . 1 g PdCl (5.64 mmol) was added
2
2
to a 250 mL conical fask with 50 mL deionized water, and
then the mixture was diluted to 100 mL with deionized water
and shaken well. 3 g activated carbon was added to the PdCl
2
solution with 1000 rpm stirring condition for 10 h, followed
by evaporation and drying at 383 K in air oven overnight. Te
obtained powder was reduced in a fow of 20% H in N at
2
2
623 K for 4 h to form fnal Pd/C catalyst.
2.3. Preparation of Ionic Liquid. 20 g 1-methylimidazole and
62 g 3-(chloropropyl)triethoxysilane (molar ratio 1 : 1.08)
were added to a 250 mL round bottom fask; the mixture
was sealed and heated in oil bath at 368 K with 1000 rpm
magnetic stirring for 24 h to form ionic liquid. Afer that, the
reaction mixture was cooled down to room temperature and
the formed ionic liquid was reserved for further use.
2.4. Preparation of Ionic Liquid Modifed Pd/C Catalyst. 2 g
Pd/C catalyst and 6.46 g ionic liquid (20 mmol) prepared in
2.3 were added to a 250 mL round bottom fask with 50 mL
toluene and were heated in oil bath at the refux temperature
with 1000 rpm magnetic stirring for 14 h and then the solid
catalyst was fltered and washed with water and ethanol,

Journal of Chemistry
3
Pd
０＞2+
．；＂（4
Reduction
Impregnation
Surface of AC
Adsorption of ０＞2+ and
difusion into AC pores
Pd/C catalyst
EtO
EtO
Heating
(％Ｎ／)3３Ｃ
N
N
Si
+
N
N
Cl
Ionic
liquid
＃Ｆ−
EtO
3-(Chloropropyl)triethoxysilane
Replacement
1-Methylimidazole
Ionic liquid
N
(％Ｎ／)3３Ｃ
+
(％Ｎ／)3３Ｃ
NaOH
N
N
N
／（−
＃Ｆ−
Alkaline ionic liquid
Ionic
liquid
Alkaline ionic
liquid
Replacement
Pd/C-＃Ｆ− catalyst
Pd/C-／（− catalyst
Functional groups
０＞2+
Substrate HMF
Product FDCA
Homogeneous base
Solid base
Pd
Ionic liquid
Alkaline ionic liquid
Scheme 2: Te schematic diagram of alkaline ionic liquid (IL) modifed Pd/C catalyst (Pd/C-OH−) synthesis.
respectively. Finally, the crude product was dried in a vacuum
oven at 323 K overnight (Sc−heme 2).
353 K, 373 K, and 393 K) with magnetic stirring at a constant
rate of 500 rpm in high-pressure cylinders. Afer reacting for
desired time (2 h, 4 h, 8 h, 12 h, and 24 h), 10 ꢀL aliquot was
collected from the reaction mixture and analyzed by HPLC.
In addition, the catalyst used in the experiment was recovered
for reuse.
2.5. Synthesis of Pd/C-OH Catalyst. Te cation exchange
of Cl− in Pd/C-Cl− with OH− was described as follows.
2 g catalyst prepared in 2.4 and 3.2 g NaOH were added to
Te furan compounds were analyzed by HPLC (Shi-
madzu Technology, model 20AB) equipped with a UV
detector. Te samples were separated at the wavelength
of 280 nm using a reverse-phase C18 column (200 mm ×
4.6 mm). Te mobile phase was composed of acetonitrile
and 0.1 wt.% acetic acid aqueous solution at the fow rate
of 0.5 mL⋅min−1. Te contents of HMF, HFCA, FFCA, and
FDCA were obtained by the calibration curves of the standard
material. Te specifc calculation was as follows:
a 150 mL Erlenmeyer fask with 50 mL H O. Te reaction
2
system was sealed and stirred at room temperature for 24 h.
Finally, the catalyst was fltered with water and dried in a
vacuum oven at 323 K overnight.
2.6. Typical Procedure for the Aerobic Oxidation of HMF
Over Pd/C-OH−. Te substrate HMF (0.08 mmol, 10 mg) was
frstly dissolved in 4 g water. A certain amount of Pd/C-OH−
catalyst (20 mg, 40 mg, 60 mg, and 80 mg) was added to the
reaction mixture quickly and oxygen was passed into the
reaction mixture for 5 min. At the end, the reaction mixture
was sealed immediately. Finally, the reaction mixture was
immersed in an oil bath at desired temperature (313 K, 333 K,
HMF conversion = moles of converted HMF/moles of
starting HMF × 100%.
HFCA yield = moles of HFCA/moles of starting HMF
× 100%.

4
Journal of Chemistry
(a)
(b)
Figure 1: SEM images of (a) Pd/C and (b) Pd/C-OH−.
FFCA yield = moles of FFCA/moles of starting HMF
1539 ＝Ｇ−1
1100 ＝Ｇ−1
× 100%.
FDCA yield = moles of FDCA/moles of starting HMF
× 100%.
2.7. Catalyst Characterization. Scanning electron microscope
(SEM) images were produced on a JSM-7500F instrument
and obtained at 30 KV with 1.4 nm image resolution. X-
ray powder difraction (XRD) patterns were measured on a
Bruker D8 Advance powder difractometer. XRD was col-
lected in the 2ꢁ range of 5∘–80∘ with a scanning rate of 2∘⋅S−1.
FT-IR measurements were recorded using a Nicolet-460
FTIR spectrometer with a spectral resolution of 0.4 cm−1 in
the wavenumber range of 400–4000 cm−1. TG was obtained
using a Rheometric Scientifc STA1500 analyzer at the tem-
perature from 323 K to 1073 K in nitrogen atmosphere to
verify the property of catalyst under thermogravimetric anal-
1270 ＝Ｇ−1
500
1000
1500
2000
2500
3000
3500
4000
Wavenumber (＝Ｇ−1
)
(a)
(b)
ysis. CO -TPD was produced on a Micromeritics AutoChem
2
Figure 2: FTIR spectra of (a) Pd/C and (b) Pd/C-OH−.
II 2920 instrument. Typically, the sample was loaded and
pretreated in a quartz reactor with high-purity Ar at 473 K for
2 h, followed by cooling down to 373 K. Ten, the temperature
was raised to 1073 K at a rate of 5 K⋅min−1.
vibration of C-N of imidazole ring and it verifed the presence
of the ionic liquid on the surface of activated carbon.
3. Results and Discussion
As shown in Figure 3, there were two distinct peaks
on the DTG curve, which had a corresponding weight loss
in the TG curve. Te frst sharp peak appeared at 373 K.
Tis peak belonged to the weightless peak of water. Te
second peak appeared between 473 K and 873 K and the tip
temperature was 710 K, indicating that the ionic liquid on the
carbon support began to decompose in this range. As the
temperature continued to rise, the rate of weight loss slowed
down, possibly corresponding to some residual ionic liquid
for further decomposition. We could fgure out the result
from the graph; the loading of ionic liquid on the surface of
Pd/C was 18.13 wt.%. In addition, the palladium loading in the
Pd/C catalyst was quantitatively determined by ICP-AES. Te
Pd content was determined to be 10 wt.%.
3.1. Characterization of Catalysts. SEM images of Pd/C and
Pd/C-OH− catalysts were shown in Figure 1. It was interesting
that there was no virtual diference in the SEM images of
the Pd/C and Pd/C-OH−. Obviously, the structure of Pd/C
has not been signifcantly damaged. In order to provide
more information about the surface functional groups of the
prepared Pd/C-OH− catalyst, it was further characterized by
FT-IR technology. As shown in Figure 2, peaks of 1100 cm−1
and 1539 cm−1 were the stretching vibration of C-O and -
COO-, respectively, which were the characteristic peaks of
activated carbon. It was pointed out that the functional
groups on the surface of activated carbon facilitated the
adsorption of Pd2+ onto the activated carbon surface [28]. Te
absorption peak at 1270 cm−1 was assigned to the stretching
XRD patterns of the Pd/C, Pd/C-Cl−, and Pd/C-OH−
catalysts were shown in Figure 4. Te peak at 23∘ (2ꢁ) was

Journal of Chemistry
5
Table 1: Te efect of catalyst dosage on the HMF oxidation.a
0.0
100
90
HMF
conversion
(%)
Catalyst
dosage (mg)
HFCA
FFCA
FDCA
−0.2
−0.4
−0.6
−0.8
−1.0
Entry
yield (%) yield (%) yield (%)
1
0
8.10
80.78
100
—
—
—
5.54
61.52
59.54
45.89
80
2
3
4
5
20
40
60
80
66.52
26.61
35.48
30.64
8.36
11.13
4.73
—
Weight loss: −18.13%
70
60
100
100
aReaction conditions: Pd/C-OH , HMF (10 mg), H O (4 g), 353 K, and 12 h.
−
2
200
400
600
800
Temperature (∘C)
Figure 3: TG spectra of Pd/C-OH−.
40∘
23∘
47∘
68∘
450
500
550
600
650
700
Temperature (∘C)
Figure 5: CO -TPD profle for Pd/C-OH−.
2
10
20
30
40
50
60
70
80
2 (∘)
(a)
(b)
(c)
the efect of catalyst dosage on the oxidation of HMF with
keeping the other operation conditions constant. Te efect
of catalyst loading was varied over the range of 0–0.08 g/cm3
on the basis of total volume of the reaction mixture [31]. As
HMF conversion and FDCA yield shown in Table 1, there was
no FDCA produced by the HMF oxidation without catalyst.
Initially, HMF conversion and FDCA yield were enhanced
as the catalyst amount increased at the same reaction time
point. For example, HMF conversions of 80.78% and 100%
were obtained afer 12 h with the catalyst amounts of 20 mg
and 40 mg; the corresponding FDCA yields were 5.54%
and 61.52%. Tis increase in HMF conversion and FDCA
yield may be due to the increase of the availability and
number of catalytically active sites as the catalyst amount
increased [32]. With further increase of the catalyst amount
to 60 mg or 80 mg, HMF conversion was almost the same
and FDCA yield decreased to 59.54% and 45.89%. Unlike
chemical reactions with homogeneous catalysts, reactions
with heterogeneous catalysts were limited by mass transfer
in the reaction system. A larger amount of catalyst made the
mass transfer of substrate HMF from the liquid solution to
the active sites slower. It may be also due to the side reaction
caused by the base concentration and reaction temperature.
Figure 4: XRD patterns of (a) Pd/C, (b) Pd/C-Cl−, and (c) Pd/C-
OH−.
the characteristic difraction peak of activated carbon. For
the Pd nanoparticles, three peaks at 40∘, 47∘, and 68∘ (2ꢁ)
were the characteristic difraction peaks of the palladium
nanoparticles. Te intensity of the peak at 40∘ (2ꢁ) was
signifcantly stronger than the other two peaks [29]. As shown
in Figure 4, the decrease of intensity of peaks at 40∘ and 47∘
(2ꢁ) and the disappearance of the peaks at 68∘ (2ꢁ) were
observed, which was attributed to the loading of ionic liquids
and OH− [30].
Te CO -TPD profle for Pd/C-OH− was shown in
2
Figure 5. It was proven that Pd/C-OH− was successfully syn-
thesized and OH− was successfully absorbed on the surface
of the Pd/C catalyst. We can see from the graph that there
was mainly one desorption peak in the CO -TPD around
2
798 K. Te base amount of Pd/C-OH− was in the range of our
research and the base amount was 2.54 mmol⋅g−1.
3.2. Efect of Catalyst Dosage on HMF Oxidation. In this
3.3. Efect of Diferent Solvents on HMF Oxidation. It has been
reported that solvents were very important in the chemical
experiment, diferent catalyst amounts were used to establish

6
Journal of Chemistry
Table 2: Te efect of reaction temperature on the HMF oxidation.a
100
80
60
40
20
0
Reaction
HMF
HFCA
FFCA
FDCA
Entry temperature conversion
yield (%) yield (%) yield (%)
(K)
313
333
353
373
393
(%)
83.12
100
100
100
1
43.46
40.97
26.61
9.76
3.75
8.44
11.13
12.81
—
35.50
50.52
61.52
76.79
78.55
2
3
4
5
100
—
aReaction conditions: Pd/C-OH (40 mg), HMF (10 mg), H O (4 g), and
−
2
12 h.
DMSO
Toluene
Ethanol
solvent
（2／
＃（3＃．
100
80
60
40
20
0
HMF conv.
FDCA yield
HFCA yield
FFCA yield
Figure 6: Efect of the solvents on the HMF oxidation. Reaction
conditions: Pd/C-OH− (40 mg), HMF (10 mg), 353 K, and 12 h.
reaction, because solvent has diferent properties, such as
polarity, dielectric constant, steric hindrance, and acid base
[33]. Tus, the oxidation of HMF was carried out in various
solvents and the results were summarized in Figure 6. We can
conclude that the solvent showed a remarkable efect on both
HMF conversion and product yield. High HMF conversion
and low FDCA yield were obtained in toluene. Te catalyst
showed high HMF conversion in aromatic solvents like
toluene. Te low FDCA yield may be because FDCA has
a high dielectric constant and was insoluble in solvents of
low polarity. Tus, FDCA yield was higher in polar solvents
than those obtained in solvents with low polarity in theory.
Interestingly, low HMF conversion and FDCA yield were
obtained in protic ethanol and DMSO; high HMF conversion
and FDCA yield were obtained in low boiling point aprotic
acetonitrile. To our delight, water was proven to be the best
solvent for the HMF oxidation. As expected, the Pd/C-OH−
catalyst showed the best catalytic performance in water. Full
HMF conversion and FDCA yield of 61.52% were achieved
in water at 353 K for 12 h. In addition, using water as a green
solvent appears to be very appealing due to its low cost and
the absence of toxic pollution.
0
5
10
15
20
25
Reaction time (h)
HMF
FFCA yield
FDCA yield
HFCA yield
Figure 7: Efect of the reaction time on the HMF oxidation.
Reaction conditions: Pd/C-OH− (40 mg), HMF (10 mg), H O (4 g),
2
and 373 K.
substrate was in contact with catalyst active sites at higher
reaction temperatures. However, increasing the reaction tem-
perature to 393 K, FDCA was the only product and there was
no other furan products produced. Te possible reason could
be that the degradation of HMF was serious at the higher
reaction temperature of 393 K. HMF was not stable at high
temperature and was degraded into byproducts [34].
3.5. Efect of Time Course on HMF Oxidation. In order to give
more insights into the aerobic HMF oxidation over Pd/C-
OH− catalyst, the oxidation of HMF at diferent reaction time
point was recorded, and the results were shown in Figure 7.
HMF conversion and FDCA yield gradually increased during
the reaction process [35]. Full HMF conversion was obtained
within 2 h. Te yield of FDCA also gradually increased
with enhancement of the reaction time, and the maximum
FDCA yield was obtained in 82.39% afer 48 h. Besides
FDCA, HFCA was also formed. Hence, we can know that the
oxidation of HMF into HFCA and the further oxidation of
HFCA into FDCA were the main reaction route for the HMF
oxidation over Pd/C-OH− catalyst.
3.4. Efects of Temperature on HMF Oxidation. As the results
shown in Table 2, the reaction temperature had a remarkable
efect on the HMF conversion and FDCA yield. Experi-
ments were carried out at diferent reaction temperatures
in the range of 313 K to 393 K. Generally speaking, we can
conclude that HMF conversion and FDCA yield increased
with increase of reaction temperature. When the temperature
is 313 K, HMF conversion and FDCA yield were 83.32%
and 35.5%, respectively. Increasing the reaction temperature
to 333 K, 353 K, and 373 K greatly enhanced the reaction
efciency. HMF conversions were almost 100% and FDCA
yields were 50.52%, 61.52%, and 76.79%. Signifcantly, more

Journal of Chemistry
7
Table 3: Te efect of base on the HMF oxidation.
Entry
1a
Base (mmol)
HMF conversion (%)
HFCA yield (%)
FFCA yield (%)
10.08
FDCA yield (%)
0
36.79
100
100
99.90
100
—
26.61
9.76
62.09
49.67
21.75
61.52
76.79
18.62
37.64
2b
0.10 (solid base)
0.10 (solid base)
0.10 (homogeneous base)
0.10 (homogeneous base)
11.13
12.81
18.70
11.42
3c
4d
5e
aReaction conditions: Pd/C (10 mg), HMF (10 mg), H O (4 g), 353 K, and 12 h. bReaction conditions: Pd/C-OH (40 mg including 10 mg Pd/C), HMF (10 mg),
−
2
H O (4 g), 353 K, and 12 h. cReaction conditions: Pd/C-OH (40 mg including 10 mg Pd/C), HMF (10 mg), H O (4 g), 373 K, and 12 h. dReaction conditions:
−
2
2
Pd/C (10 mg), 4 mg NaOH, HMF (10 mg), H O (4 g), 353 K, and 8 h. eReaction conditions: Pd/C (10 mg), 4 mg NaOH, HMF (10 mg), H O (4 g), 353 K, and
2
2
12 h.
3.6. Efect of Base on HMF Oxidation. Base played an impor-
tant role in the oxidation of HMF into FDCA. One important
reason for the use of base was that base can be used
to neutralize the FDCA, avoiding FDCA adsorbed on the
surface of catalyst. Te salt of FDCA was dissolved in the
reaction solution and kept the catalyst activity stable [36].
Te results were shown in Table 3. Under the same reaction
condition, HMF oxidation was carried out over Pd/C, Pd/C
with homogeneous base, and Pd/C-OH−, respectively, with
the corresponding FDCA yields of 21.75%, 37.64%, and
61.52%. Hence, we can conclude that base was helpful to
achieve rapid conversion of HMF to the FDCA and Pd/C-
OH− catalyst showed a remarkable efect on HMF oxidation.
100
80
60
40
20
0
1
2
3
4
5
3.7. Catalyst Recycling Experiments. To verify the recycla-
bility and stability of heterogeneous catalysts, the recycling
experiments of the Pd/C-OH− were carried out at 373 K with
40 mg catalyst for 12 h. Afer the reaction, the supernatant was
removed. Te catalyst was washed with water and ethanol
twice. Finally, the catalyst was dried in a vacuum oven at
323 K. Ten the spent catalyst was reused for the next cycle
under the same reaction conditions. Te results were shown
in Figure 8. HMF conversions and FDCA yields decreased
with the cycle of the catalyst. Tis may be due to the loss
of OH− on the surface of the catalyst, which belonged to
physical adsorption rather than covalent binding. On the
other hand, it may be also due to the reduction of catalyst
activity. Tere was a small decrease in the FDCA yield of the
frst and second run. However, HMF conversion and FDCA
yield were observed to show a signifcant decrease from 100%
and 61.96% in the second run to 60.46% and 26.27% in the
third run. Ten, there was a small decrease in the HMF
conversion and FDCA yield of the next runs.
Reaction run
HMF conv.
FDCA yield
Figure 8: Recycle experiments of the catalyst. Reaction conditions:
Pd/C-OH− (40 mg), HMF (10 mg), 373 K, H O (4 g), and 12 h.
2
process for aqueous HMF oxidation was reported using
solid base modifed activated carbon-supported palladium
nanoparticle catalyst (Pd/C-OH−).
Conflicts of Interest
Te authors declare that the received funding did not lead
to any conficts of interest regarding the publication of this
manuscript.
Acknowledgments
4. Conclusion
Tis work was funded by the National Natural Science
Foundation of China (nos. 31170672, 21406093, and 21676125),
the Natural Science Foundation of Jiangsu Province
(BK20140529), Key University Science Research Project
of Jiangsu Province (14KJB530001), China Postdoctoral
Science Foundation (2014T70489, 2013M541621, 1302152C,
and 2014M550271), Six Talent Peaks Project in Jiangsu
Province (2015-NY-016), Foundation for the Eminent Talents
and Research Foundation for Advanced Talents of Jiangsu
University (12JDG074 and 14JDG014), and the Project
In summary, the Pd/C-OH− catalyst was successfully pre-
pared and characterized by SEM, XRD, TG, FT-IR, and
CO -TPD technologies. Te catalyst showed high catalytic
2
activity in the HMF oxidation and reaction temperature,
reaction time, catalyst amount, and solvent greatly afected
the oxidation of HMF. Under optimal reaction conditions,
high HMF conversion of 100% and FDCA yield of 82.39%
were achieved over Pd/C-OH− catalyst in water at 373 K
for 24 h. A much more environmentally benign and green

8
Journal of Chemistry
Funded by the Priority Academic Program Development of
Jiangsu Higher Education Institutions.
[15] T. Miura, H. Kakinuma, T. Kawano, and H. Matsuhisa, “Prepa-
ration of furan-2,5-dicarboxylic acid by oxidizing furan ring
compounds,” U.S. Patent. US-7411078, 2008.
[16] B. Saha, S. S. Dutta, and M. M. Abu-Omar, “Aerobic oxidation
of 5-hydroxylmethylfurfural with homogeneous and nanopar-
ticulate catalysts,” Catalysis Science & Technology, vol. 2, no. 1,
pp. 79–81, 2011.
[17] W. Niu, D. Wang, G. Yang et al., “Pt nanoparticles loaded
on reduced graphene oxide as an efective catalyst for the
direct oxidation of 5-hydroxymethylfurfural (HMF) to produce
2,5-furandicarboxylic acid (FDCA) under mild conditions,”
Bulletin of the Chemical Society of Japan, vol. 87, no. 10, pp. 1124–
1129, 2014.
References
[1] A. Corma Canos, S. Iborra, and A. Velty, “Chemical routes
for the transformation of biomass into chemicals,” Chemical
Reviews, vol. 107, no. 6, pp. 2411–2502, 2007.
[2] S. De, B. Saha, and R. Luque, “Hydrodeoxygenation processes:
Advances on catalytic transformations of biomass-derived plat-
form chemicals into hydrocarbon fuels,” Bioresource Technol-
ogy, vol. 178, pp. 108–118, 2015.
[3] J. B. Binder and R. T. Raines, “Simple chemical transformation
of lignocellulosic biomass into furans for fuels and chemicals,”
Journal of the American Chemical Society, vol. 131, no. 5, pp.
1979–1985, 2009.
[4] Y. Jiang, W. Chen, Y. Sun et al., “One-pot conversion of biomass-
derived carbohydrates into 5-[(formyloxy)methyl]furfural: A
novel alternative platform chemical,” Industrial Crops and
Products, vol. 83, pp. 408–413, 2016.
[5] C. Cai, Q. Liu, J. Tan, T. Wang, Q. Zhang, and L. Ma, “Conver-
sion of Cellulose to 5-Hydroxymethylfurfural using Inorganic
Acidic Catalysts in the Presence of Pressurized Water Steam,”
Bioresources, vol. 12, no. 1, 2016.
[6] S. Hu, Z. Zhang, J. Song, Y. Zhou, and B. Han, “Efcient
conversion of glucose into 5-hydroxymethylfurfural catalyzed
by a common Lewis acid SnCl4 in an ionic liquid,” Green
Chemistry, vol. 11, no. 11, pp. 1746–1749, 2009.
[18] D. K. Mishra, H. J. Lee, J. Kim et al., “MnCo2O4 spinel
supported ruthenium catalyst for air-oxidation of HMF to
FDCA under aqueous phase and base-free conditions,” Gr
Chemistry, vol. 19, no. 7, pp. 1619–1623, 2017.
een
[19] O. Casanova, S. Iborra, and A. Corma, “Biomass into chem-
icals: aerobic oxidation of 5-hydroxymethyl-2-furfural into
2,5-furandicarboxylic acid with gold nanoparticle catalysts,”
ChemSusChem, vol. 2, no. 12, pp. 1138–1144, 2009.
[20] Z. Zhang, J. Zhen, B. Liu, K. Lv, and K. Deng, “Selec-
tive aerobic oxidation of the biomass-derived precursor 5-
hydroxymethylfurfural to 2,5-furandicarboxylic acid under
mild conditions over a magnetic palladium nanocatalyst,” Green
Chemistry, vol. 17, no. 2, pp. 1308–1317, 2015.
[21] Y. Xu, H. Bai, G. Lu, C. Li, and G. Shi, “Flexible graphene flms
via the fltration of water-soluble noncovalent functionalized
graphene sheets,” Journal of the American Chemical Society, vol.
130, no. 18, pp. 5856-5857, 2008.
[7] Z. Zhang and Z. K. Zhao, “Microwave-assisted conversion of
lignocellulosic biomass into furans in ionic liquid,” Bioresource
Technology, vol. 101, no. 3, pp. 1111–1114, 2010.
[22] K. S. Kim, P. Tarakeshwar, and J. Y. Lee, “Molecular clusters of
ꢄ-systems: theoretical studies of structures, spectra, and origin
of interaction energies,” Chemical Reviews, vol. 100, no. 11, pp.
4145–4185, 2000.
[8] W. Li, Z. Xu, T. Zhang et al., “Catalytic conversion of biomass-
derived carbohydrates into 5-hydroxymethylfurfural using a
strong solid acid catalyst in aqueous ꢂ-valerolactone,” Biore-
sources, vol. 11, no. 3, pp. 5839–5853, 2016.
[23] S. E. Davis, L. R. Houk, E. C. Tamargo, A. K. Datye, and R. J.
Davis, “Oxidation of 5-hydroxymethylfurfural over supported
Pt, Pd and Au catalysts,” Catalysis Today, vol. 160, no. 1, pp. 55–
60, 2011.
[9] L. Hu, L. Lin, Z. Wu, S. Zhou, and S. Liu, “Recent
advances in catalytic transformation of biomass-derived
5-hydroxymethylfurfural into the innovative fuels and
chemicals,” Renewable & Sustainable Energy Reviews, vol. 74,
pp. 230–257, 2017.
[24] J. Nie, J. Xie, and H. Liu, “Activated carbon-supported ruthe-
nium as an efcient catalyst for selective aerobic oxidation of 5-
hydroxymethylfurfural to 2,5-diformylfuran,” Chinese Journal
of Catalysis, vol. 34, no. 5, pp. 871–875, 2013.
[25] X. Wan, C. Zhou, J. Chen et al., “Base-free aerobic oxidation
of 5-hydroxymethyl-furfural to 2,5-furandicarboxylic acid in
water catalyzed by functionalized carbon nanotube-supported
Au–Pd alloy nanoparticles,”ACS Catalysis, vol. 4, no. 7, pp. 2175–
2185, 2014.
[26] B. N. Zope, S. E. Davis, and R. J. Davis, “Infuence of reaction
conditions on diacid formation during Au-catalyzed oxidation
of glycerol and hydroxymethylfurfural,” Topics in Catalysis, vol.
55, no. 1-2, pp. 24–32, 2012.
[27] P. J. Dyson, M. C. Grossel, N. Srinivasan et al., “Organometallic
synthesis in ambient temperature chloroaluminate(III) ionic
liquids. Ligand exchange reactions of ferrocene,” Journal of the
Chemical Society - Dalton Transactions, no. 19, pp. 3465–3469,
1997.
[10] O. Casanova, S. Iborra, and A. Corma, “Chemicals from
biomass: Etherifcation of 5-hydroxymethyl-2-furfural (HMF)
into 5,5ꢃ(oxy-bis(methylene))bis-2-furfural (OBMF) with solid
catalysts,” Journal of Catalysis, vol. 275, no. 2, pp. 236–242, 2010.
[11] S. P. Verevkin, V. N. Emel’yanenko, E. N. Stepurko, R. V.
Ralys, D. H. Zaitsau, and A. Stark, “Biomass-derived platform
chemicals: Termodynamic studies on the conversion of 5-
hydroxymethylfurfural into bulk intermediates,” Industrial &
Engineering Chemistry Research, vol. 48, no. 22, pp. 10087–
10093, 2009.
[12] J. Keskiva¨li, P. Wrigstedt, K. Lagerblom, and T. Repo, “One-step
Pd/C and Eu(OTf)3 catalyzed hydrodeoxygenation of branched
C11 and C12 biomass-based furans to the corresponding alka-
nes,” Applied Catalysis A: General, vol. 534, pp. 40–45, 2017.
[13] N. Jacquel, R. Saint-Loup, J.-P. Pascault, A. Rousseau, and F.
Fenouillot, “Bio-based alternatives in the synthesis of aliphatic-
aromatic polyesters dedicated to biodegradable flm applica-
tions,” Polymer (United Kingdom), vol. 59, pp. 234–242, 2015.
[14] D. Yan, J. Xin, C. Shi et al., “Base-free conversion of 5-
hydroxymethylfurfural to 2,5-furandicarboxylic acid in ionic
liquids,” Chemical Engineering Journal, vol. 323, pp. 473–482,
2017.
[28] B. Liu, Y. Ren, and Z. Zhang, “Aerobic oxidation of 5-
hydroxymethylfurfural into 2,5-furandicarboxylic acid in water
under mild conditions,” Green Chemistry, vol. 17, no. 3, pp. 1610–
1617, 2015.
[29] Y.-M. Lu, H.-Z. Zhu, W.-G. Li, B. Hu, and S.-H. Yu, “Size-
controllable palladium nanoparticles immobilized on carbon

Journal of Chemistry
9
nanospheres for nitroaromatic hydrogenation,” Journal of Mate-
rials Chemistry A, vol. 1, no. 11, pp. 3783–3788, 2013.
[30] N. Mei, B. Liu, J. Zheng, K. Lv, D. G. Tang, and Z. H. Zhang,
“A novel magnetic palladium catalyst for the mild aerobic oxi-
dation of 5-hydroxymethylfurfural into 2, 5-furandicarboxylic
acid in water,” Catalysis Science Technology, vol. 5, no. 6, pp.
3194–3202, 2015.
[31] G. D. Yadav and R. V. Sharma, “Biomass derived chem-
icals: Environmentally benign process for oxidation of 5-
hydroxymethylfurfural to 2,5-diformylfuran by using nano-
fbrous Ag-OMS-2-catalyst,” Applied Catalysis B: Environmen-
tal, vol. 147, pp. 293–301, 2014.
[32] Z. Zhang, Z. Yuan, D. Tang, Y. Ren, K. Lv, and B. Liu, “Iron oxide
encapsulated by ruthenium hydroxyapatite as heterogeneous
catalyst for the synthesis of 2,5-diformylfuran,” ChemSusChem,
vol. 7, no. 12, pp. 3496–3504, 2014.
[33] R. R. Sever and T. W. Root, “DFT study of solvent coordination
efects on titanium-based epoxidation catalysts. Part one: For-
mation of the titanium hydroperoxo intermediate,” Te Journal
of Physical Chemistry B, vol. 107, no. 17, pp. 4080–4089, 2003.
[34] K. R. Vuyyuru and P. Strasser, “Oxidation of biomass derived 5-
hydroxymethylfurfural using heterogeneous and electrochemi-
cal catalysis,” Catalysis Today, vol. 195, no. 1, pp. 144–154, 2012.
[35] L. Gao, K. Deng, J. Zheng, B. Liu, and Z. Zhang, “Efcient
oxidation of biomass derived 5-hydroxymethylfurfural into 2,5-
furandicarboxylic acid catalyzed by Merrifeld resin supported
cobalt porphyrin,” Chemical Engineering Journal, vol. 270, pp.
444–449, 2015.
[36] L. Ardemani, G. Cibin, A. J. Dent et al., “Solid base catalysed
5-HMF oxidation to 2,5-FDCA over Au/hydrotalcites: fact or
fction?” Chemical Science, vol. 6, no. 8, pp. 4940–4945, 2015.

Journal of
Nanomaterials
Journal of
International Journal of
The Scientifc
Journal of
Analytical Methods
Photoenergy
in Chemistry
World Journal
Applied Chemistry
Hindawi
Hindawi
Hindawi
Hindawi Publishing Corporation
Hindawi
www.hindawi.com
www.hindawi.com
Volume 2018
www.hindawi.com
Volume 2018
hw
t
w
tp
w
:/./h
w
in
w
d
w
aw.hii.ncodmawi.com
Volume 20183
Volume 2018
www.hindawi.com
Volume 2018
Advances in
International Journal of
Physical Chemistry
Medicinal Chemistry
Hindawi
www.hindawi.com
Hindawi
Volume 2018
www.hindawi.com
Volume 2018
Submit your manuscripts at
www.hindawi.com
Journal of
Bioinorganic Chemistry
and Applications
Materials
Hindawi
Hindawi
www.hindawi.com
Volume 2018
www.hindawi.com
Volume 2018
International Journal of
Advances in
Journal of
International Journal of
BioMed
Tribology
Chemistry
Research International
Spectroscopy
Electrochemistry
Hindawi
Hindawi
Hindawi
www.hindawi.com
Hindawi
Hindawi
www.hindawi.com
www.hindawi.com
Volume 2018
www.hindawi.com
Volume 2018
Volume 2018
www.hindawi.com
Volume 2018
Volume 2018
Enzyme
Research
Journal of
Journal of
Biochemistry
Spectroscopy
Nanotechnology
Research International
Hindawi
Hindawi
www.hindawi.com
Hindawi
www.hindawi.com
Hindawi
www.hindawi.com
www.hindawi.com
Volume 2018
Volume 2018
Volume 2018
Volume 2018