A water-tolerant C16H3PW11CrO39 catalyst for the efficient conversion of monosaccharides into 5-hydroxymethylfurfural in a micellar system

Article abstract of DOI:10.1039/c3ra43408g

A water-tolerant cetyltrimethyl ammonium salt of transition metal (Cr(iii)) substituted polyoxometalate C₁₆H₃PW₁₁CrO ₃₉ (C₁₆ = cetyltrimethyl ammonium) has been designed and used for the conversion of fructose and glucose into 5-hydroxymethylfurfural (HMF). The catalyst shows high conversion efficiency (90.3% and 84.2%, respectively) and high yields (40.6% and 35.2%, respectively) due to its dual acidity and hydrophobicity. The catalyst is stable during an aqueous-phase reaction and can be recycled via a simple separation process.

Full text of DOI:10.1039/c3ra43408g

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A water-tolerant C H PW CrO catalyst for the
1
6 3
11
39
efficient conversion of monosaccharides into
-hydroxymethylfurfural in a micellar system†
Cite this: RSC Adv., 2013, 3, 23051
5
a
a
a
a
a
Hongwei Zheng, Zhong Sun, Xiaohu Yi, Shengtian Wang, Jianxin Li,
a
b
Xiaohong Wang* and Zijiang Jiang*
A water-tolerant cetyltrimethyl ammonium salt of transition metal (Cr(III)) substituted polyoxometalate
PW11CrO39 (C16 ¼ cetyltrimethyl ammonium) has been designed and used for the conversion of
fructose and glucose into 5-hydroxymethylfurfural (HMF). The catalyst shows high conversion efficiency
90.3% and 84.2%, respectively) and high yields (40.6% and 35.2%, respectively) due to its dual acidity
16 3
C H
Received 4th July 2013
Accepted 24th September 2013
(
DOI: 10.1039/c3ra43408g
and hydrophobicity. The catalyst is stable during an aqueous-phase reaction and can be recycled via a
www.rsc.org/advances
simple separation process.
At present, efficient HMF production from glucose or cellu-
lose is challenging because the isomerization of glucose into
1. Introduction
Developing new strategies for converting carbohydrates into
-hydroxymethylfurfural (HMF) has attracted much attention
because of fossil resource depletion in this decade. The recent
fructose using Brønsted acids is usually inefficient with a low
HMF yield. By now, conversion of glucose to HMF using some
Lewis acid catalysts has been reported. The catalysts include
5
1,2
14
15
16
developments showed that high fructose dehydration effi- homogeneous ones such as AlCl3, CrCl2, and MgCl ,
2
18
ciency could be obtained with homogeneous or heterogeneous heterogeneous ones such as Nb O (ref. 17) and Ta O , and
2
5
2 5
3
4
catalysts. These catalysts include mineral acids, zeolites, ion dual acid systems that consist of a Lewis acid and a Brønsted
5
6
20
exchange resins, metal chlorides (Cr, Al, Ge and Zn, et al.),
2 5 2 3 4 3
acid such as Nb O $nH O/H PO (ref. 19) and AlCl /HCl. In a
7
8
metal oxides, mesoporous silica materials, sulfonated carbon dual acid system, the Brønsted acid is added to conrm the
9
10
11
materials, heteropolyacids (HPAs), and ionic liquids. It was
reported that CrCl2 was effective for HMF production from
fructose in ionic liquids and an HMF yield up to 97% could be
fructose dehydration. Accordingly, the HMF yield can be
increased signicantly when catalyst containing both
a
Brønsted and Lewis acid sites is used.
6
achieved. The reaction has been explored in different solvent
HPAs represent a candidate for designing water-tolerant and
systems such as organic solvents, sub- and supercritical water, dual acidic (Lewis and Brønsted) catalysts with hydrophobic
organic–water mixtures, biphasic water–organic systems, and surroundings around HPAs. Shimizu et al. have investigated the
ionic liquids. The aqueous process is the most economical and hydrolysis of cellobiose and cellulose using the metal salts of
21
greenest technology when compared with other technologies. HPA catalysts with Brønsted and Lewis acids. Our group has
However, water generally interacts with traditional support
investigated the catalytic activity of the dodecatungstopho-
12
22,23
materials such as alumina and poisons acid sites. In addition,
-HMF can further react with water to produce levulinic acid
phoric acid and its cesium or silver salts
fructose or glucose to HMF. We found that the silver salts of the
and formic acid. Therefore, the development of new water- dodecatungstophophoric acid (Ag PW O ) were active in
on dehydration of
5
13
3
12 40
tolerant solid acids (such as heterogeneous catalysts) that dehydration of fructose and glucose to HMF due to its moderate
23
inhibit further decomposition of HMF is the key to the aqueous- Lewis acidity. The results showed that HMF yields were high in
phase HMF production.
the water–methyl isobutyl ketone (MIBK) biphasic system,
ꢀ
ꢀ
being 77.7% at 120 C for 60 min and 76.3% at 130 C for 4 h.
However, the HMF production in MIBK is not preferred because
of the economic and environmental reasons.
a
Key Lab of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry,
Herein, we designed a Brønsted–Lewis–surfactant-combined
C H PW CrO (H O) (abbreviated as C H PW Cr). The
Northeast Normal University, Changchun 130024, P. R. China. E-mail:
1
6
3
11
39
2
16
3
11
wangxh665@nenu.edu.cn; Fax: +86-431-85099759; Tel: +86-431-88930042
catalyst has the following advantages: (1) availability of
Brønsted and Lewis acids for isomerization and dehydration of
glucose into HMF; (2) fewer conversion of HMF with its
hydrophobic surroundings, resulting in high HMF yields in the
b
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun
1
†
1
30022, P. R. China. E-mail: jzj2002@sohu.com; Tel: +86-431-85262452
Electronic supplementary information (ESI) available. See DOI:
0.1039/c3ra43408g
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water system; (3) concentration of substrates around the cata- hexadecyltrimethylammonium bromide (CTAB) aqueous solu-
lytic sites by the formation of micellar assembles; (4) stability in tion into a 10 mL, 40 mM of H [PW CrO (H O)] solution with
4
11
39
2
water or solvents for reuse; and (5) less leaching of Cr or W stirring. The green precipitate formed immediately and was
ꢀ
atoms for environmental friendliness. These characteristics ltered before being dried at 50 C for about 3 h. The elemental
meet the modern requirements for “green catalysis”. To support analyses of C16
3
H PW11Cr are: W, 66.76; P, 1.10; Cr, 1.68; C, 7.42;
our hypotheses, C16 PW11Cr was employed as a heteroge- H, 1.51; and N, 0.40%, respectively, which gave the formula as
H
3
neous catalyst to convert monosaccharides into HMF in
aqueous and organic solvent systems.
16 3
C H PW11Cr.
2.3 Dehydration reaction
2
. Material and methods
In a typical reaction protocol, a 30 wt% fructose solution,
0
.1 mmol acid catalyst, and solvent were mixed in a 50 mL Parr
2.1 Materials and analytical methods
ꢀ
reactor. The experiment was carried out for 90 min at 130 C in
an electrically-heated oil bath, which took 20 min from room
temperature to 130 C. The reaction was stopped aer rapidly
All used solvents and chemicals were obtained from commer-
cial suppliers, which were used without any purication.
Elemental analysis was carried out using a Leeman Plasma Spec
ꢀ
cooling the reactor in an ice bath and keeping it for 30 min at
(I) Inductively Coupled Plasma Emission Spectrometer (ICP-ES)
ꢀ
0
C. The whole process was repeated three times. The catalyst
and a P-E 2400 CHN elemental analyzer. IR spectra (4000–
was centrifuged and rinsed with water three times to remove
ꢁ
1
500 cm ) were recorded in KBr discs on a Nicolet Magna 560 IR
sugar that was not reacted, and then it was calcinated for 3 h at
spectrometer. DR-UV-vis spectra (200–800 nm) were recorded
ꢀ
5
0 C to remove water. The total leaching amount of catalyst by
3
1
on a Cary 500 UV-vis-NIR spectrophotometer. The P magic-
angle spinning (MAS) spectra of the sample were recorded on a
Bruker AVANCE III 400 WB spectrometer equipped with a 4 mm
standard bore CP/MAS probehead whose X channel was tuned
to 100.62 MHz. The critical micellar concentration (CMC) of
six runs of reaction was detected using a Leeman Plasma Spec
I) ICP-ES.
(
3. Results and discussion
C H PW Cr was determined by a plot of conductivity versus 3.1 Characterization of the catalyst
1
6
3
11
concentration using the conductometer model DDS-11A.
Centrifugation was performed on T4C Centrifuge (4000 rpm,
The FT-IR spectrum of C16
in Fig. 1. The peaks in the IR spectral range of 600–1100 cm
corresponding to Keggin structural vibrations could be easily
distinguished at 1087, 972, 891, and 805 cm , respectively. The
H
3
PW11Cr was investigated, as shown
ꢁ1
5
min, Beijing Yiyao). Thermogravimetric (TGA) and differential
thermal analysis (DTA) using a Shimadzu DT 50 thermal
ꢁ1
ꢀ
analyzer. The experiments were performed up to 700 C at a
peaks were attributed to the asymmetry vibrations P–Oa
ꢀ
ꢁ1
3
ꢁ1
heating rate of 10 C min under nitrogen ow (20 cm min ),
using 0.02–0.025 g of sample, respectively. The saccharide
consumption was measured by high-performance liquid chro-
matography (HPLC, Shimadzu LC-10A) conducted on a system
equipped with a refractive index detector according to the
saccharide concentration in the aqueous phase. The saccharide
was quantied by HPLC with the Aminex HPX-87H column at
the column temperature of 303 K using MilliQ water (pH ¼ 2) at
(internal oxygen connecting P and W), W–O (terminal oxygen
d
bonding to W atom), W–Ob (edge-sharing oxygen connecting
W), and W–O
c
(corner-sharing oxygen connecting W
3
O
13 units),
of
respectively.
Compared to the spectrum
25,26
K
4
[PW11CrO39(H
2
O)],
the characteristic peaks did not shi,
conrming that C16
H
3
PW11Cr maintained the Keggin structure.
3
The DR-UV-vis spectrum of C16H PW11Cr gave two broad peaks
ꢁ
1
a ow rate of 0.6 mL min as the mobile phase. The HMF
concentration in the aqueous solution was determined by HPLC
using a UV detector. The concentration was obtained with the
ION-300H column at a column temperature of 303 K and with a
2
0
: 8 v/v methanol : water (pH ¼ 2) gradient at a ow rate of
ꢁ1
.7 mL min . The HMF concentration in the organic solution
was determined by gas chromatography (GC, Agilent 6890)
equipped with the Agilent 19091J-416 capillary column and a

ame ionization detector.
2.2 Preparation of the catalyst
K
4
[PW11CrO39(H O)] was prepared according to the ref. 24. The
2
+
+
K was replaced by H to obtain H
exchange resin: 1 g of K [PW11CrO39(H
0 mL water to form clear solution. Then the above solution was
passed through cation exchange resin (10 g). In order to conrm
4
[PW11CrO39(H
2
O)] by cation
4
2
O)] was dissolved in
2
+
+
that all K were replaced by H , a large excess of resin was used.
3
PW11Cr was prepared by adding a 10 mL, 40 mM of Fig. 1 IR spectrum of C16H PW11Cr.
C
16
H
3
2
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at 260 nm and 630 nm, as shown in Fig. S1.† The rst peak at Brønsted and Lewis acid sites were calculated based on pub-
ꢁ
1
2
60 nm was assigned to the Ob,c / W charge transfer band of lished extinction coefficients for the bands at 1545 cm and
ꢁ
1
29
POM. The broad envelope centered at 630 nm was typical for 1454 cm (Table 1). The total acid amount of C H PW Cr
octahedral chromium(III) complexes and could be assigned to was 0.83 mmol mmol , which was measured by means of
1
6
3
11
24
ꢁ1
30
spin-allowed transitions to the excited quarter state.
TG/TGA diagram (Fig. S2†) of C16 PW11Cr displayed two
peaks at 394 C and 412 C, which were due to the decompo- 3.2 Dehydration of fructose
titration.
H
3
ꢀ
ꢀ
sition of cetyltrimethyl ammonium and POM.
Fructose can be dehydrated into HMF with Brønsted acid.
KH PW11Cr, (C16 PW11Cr and C16 PW11Cr was investi-
gated as catalysts for dehydration of fructose at 403 K in
-butanol and water. Table 1 showed that the fructose conver-
sion in water decreased in the following sequence: KH CrPW11
91.4%) > C16 CrPW11 (90.3%) > (C16 CrPW11 (74.8%). First
3
The TEM image of C16H PW11Cr indicated the formation of
3
)
2
H
2
H
3
micellar-like aggregations (Fig. 2). The particle diameters were
in the range of 50–100 nm. The EDAX results (Fig. S3†) sug-
gested the molar ratio of P : W : Cr is 1.4 : 8.9 : 1. The critical
micelle concentration (CMC) of C16H PW11Cr was 0.92 mM, as
3
shown in the plot of conductivity versus concentration (Fig. S4†).
1
3
(
H
3
2 2
) H
of all this order is an agreement with solubility of these catalysts
in water. KH PW Cr was soluable in water at reaction condi-
The CMC was determined at break points of nearly two straight-
line portions of the conductivity versus concentration. This
3
11
27
tion, which was homogeneous. C H CrPW
and
16 2 2
(C ) H CrPW11 formed micellar assembly during the reaction,
1
6
3
11
indicated the formation of C16
solutions.
3
H PW11Cr micelles in aqueous
which were heterogeneous. Secondly, this order can be related
with the different of specic surface area in reaction medium
that can affects the adsorption of reagents. Table 1 showed that
the HMF selectivity in water decreased in the following
The surface acidity of C H PW Cr was determined by
1
6
3
11
pyridine adsorption infrared spectroscopy at room temperature
Py-IR), as shown in Fig. S5.† The IR spectrum exhibited a strong
(
ꢁ1
28
band at 1450 cm , which was attributed to the Lewis sites,
sequence: (C ) H CrPW (73.0%) > C H CrPW (45.0%) >
ꢁ
1
16 2
2
11
16
3
11
and another peak at 1540 cm , which was attributed to the
Brønsted sites. The result showed that C16 PW11Cr possessed
both Lewis sites and Brønsted sites. The concentrations of the
KH CrPW (36.3%). This order is an agreement with hydro-
3
11
H
3
phobic of these catalysts. The micellar prevented HMF from
31
further decomposition due to the hydrophobic property.
PW11Cr (two hydrophobic chains) shows higher
hydrophobicity than C16 PW11Cr (one hydrophobic chain).
And KH PW11Cr is hydrophilic. Moreover, the acid sites of these
16 2 2
(C ) H
H
3
3
catalysts can affects the catalytic activity. Hara et al. reported
that the solid catalysts with both Brønsted acid sites and Lewis
acid sites can facilitate the conversion of glucose into HMF and
the Brønsted acid sites play relatively insignicant role for the
17
2 2
reaction. (C16) H PW11Cr has relatively strong Lewis acid sites
and relatively weak Brønsted acid sites, which can improve the
HMF yield and selectivity. The HMF yield in water decreased in
the following sequence: (C16
)
2
H
2
CrPW11 (54.7%)
>
C
16
H
3
CrPW11 (40.6%) > KH CrPW11 (33.2%). This is due to the
3
above factors (conversion and selectivity). A high initial
concentration of fructose may increase the amount of side-
32
products. Polar aprotic solvents (such as DMSO, n-butanol)
33
had been used to improve the HMF selectivity. In this work,
HMF yield were higher in n-butanol than in water when using
(C
16
)
2
H
2
PW11Cr or
16 3
C H PW11Cr. Nevertheless, the HMF
3
Fig. 2 TEM image of C16H PW11Cr.
production in the water system is much more valuable. The
a
Table 1 The activity and selectivity of different catalysts for fructose dehydration
b
c
d
Catalyst
KH CrPW11
CrPW11
CrPW11
BA
LA
TA
Solvent
Conversion (%)
Yield (%)
Selectivity (%)
3
1.78
1.97
1.75
0.26
0.30
0.32
2.33
2.51
2.15
n-Butanol
Water
n-Butanol
Water
n-Butanol
Water
100
91.4
100
90.3
88.6
74.8
61.1
33.2
73.2
40.6
67.1
54.7
61.1
36.3
73.2
45.0
75.7
73.0
C
16
H
3
(C
16
)
2
H
2
a
ꢀ
b
ꢁ1
c
Reaction condition: 0.6 g of fructose, 0.1 mmol of catalyst, 2 g of solvent, 130 C, 90 min. Brønsted acid amount (mmol mmol ). Lewis acid
ꢁ1
d
ꢁ1
amount (mmol mmol ). Total acid content (mmol mmol ).
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sequence of conversion, selectivity and yield in 1-butanol agreed
with the sequence in water, which can be explained with the
same reasons.
C H PW Cr is an amphiphilic molecule consisting of a
1
6
3
11
hydrophilic head group PW11Cr and a hydrophobic tail hexa-
34
decyl trimethyl. From our previous report,
16 3
C H PW11Cr could
enrich the concentration of substrates on the catalytic sites to
accelerate the reaction. The IR spectra of fructose adsorption on
C H PW11Cr conrmed the assembly of fructose on the HPA
16 3
head region (Fig. S6†). W–O bands (terminal oxygen bonding
d
to W atom) shied when adsorb fructose. It indicated that the
interaction between the oxygen atom of the substrate and the
terminal oxygen atom of C16
3
H PW11Cr. The stability of HMF in
the catalytic systems was examined by heating the mixture of
5
0 mg HMF, 4 mL water and 0.1 mmol catalyst (C16
H
3
PW11Cr or
ꢀ
(C
16
)
2
H
2
PW11Cr) in a steel autoclave at 130 C (Fig. 3a). HMF
was decomposed into levulinic acid (LA) (Fig. 3b) and furfural
(
(
FA) (Fig. 3c). The decomposition was slower with
C ) H PW Cr due to the two hydrophobic chains and the
1
6 2
2
11
weaker Brønsted acid sites.
2 2 3
The performance of (C16) H PW11Cr and C16H PW11Cr for
fructose dehydration in water was examined at different
temperatures (Fig. 4). It was found that a higher temperature
could promote fructose dehydration. The HMF yield for
16 3
C H PW11Cr was 53.3% when fructose conversion was 100% at
ꢀ
C for 90 min. The highest the HMF yield for
140
(
1
C ) H PW Cr was 58.8% with 86.9% fructose conversion at
30 C for 120 min. 58.8% is the highest HMF yield in this work.
1
6 2
ꢀ
2
11
The reported catalytic system in single phase (water) showed
14
that the yield with AlCl
3
was 22%.
3.3 Conversion of glucose into HMF
Glucose conversion is more complex than fructose in the water
system. It is instructive to compare our system with other
systems (Table 2). Brønsted acid catalysts (H PW12O40 and
3
hydrochloric acid) produce trace HMF but instead yield levu-
linic and formic acids in the water system due to hydration
17
ability of Brønsted acids.
16 3
C H PW11Cr gave a 35.2% HMF
yield with 84.2% glucose conversion efficiency, which is
19
comparable to Nb O $nH O/H PO . It should be noted that
2
5
2
3
4
the unknown species (polymerization products) is reduced
signicantly with PW11Cr. Compared with the
KH PW11Cr, C16 PW11Cr exhibited better performance due to
same reasons for Table 1.
16 3
C H
3
H
3
3.4 Reusability of the catalyst
The catalyst could be easily separated from the mixture and
reused by washing with water. As shown in Fig. 5, the recycled
catalyst retained high activity for the dehydration of fructose to
HMF aer six times. The fructose conversion efficiency and
HMF yield for all runs remained about 90% and 40%, respec-
3
tively. The leaching of C16H PW11Cr was measured by ICP-AES
and the result showed the leaching rate was 0.4% during cata-
lyst cycles.
Fig.
3
The stability of HMF in water containing
16 3
C H PW11Cr and
(
C
16
)
2
H
2
PW11Cr. (a) The content of HMF, (b) the content of levulinic acid, (c) the
content of furfural.
To verify the catalytic processes, we performed the leaching
ꢀ
test. Firstly, C16
H
3
PW11Cr was heated in water at 130 C for
2
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Fig. 4 The influence of temperature and reaction time on the conversion of fructose under the reaction conditions as: 0.6 g of fructose, 0.1 mmol of catalyst, 2 g of
water. (a) C16 PW11Cr as a catalyst, and (b) (C16 PW11Cr as a catalyst.
H
3
2 2
) H
a
Table 2 The activity and selectivity of different catalysts for glucose dehydration in water
Selectivity
to HMF (%)
Selectivity
to LA (%)
Selectivity
to FA (%)
b
c
Catalyst
BA
LA
Conversion (%)
Unknown (%)
H
3
PW12
HCl
KH
O
40
1.0
—
—
0.26
0.30
0.032
81.5
93.3
76.1
84.2
78.6
1.5
2.1
32.9
41.8
44.6
36.7
17.2
20.3
19.7
5.0
45.7
3.9
31.4
26.5
1.1
16.1
76.8
15.4
12.0
49.3
d
0.36
1.78
1.97
3
CrPW11
CrPW11
$nH O/H
16 3
C H
Nb
d
d
2
O
5
2
3
PO
4
0.012
a
ꢀ
b
ꢁ1
c
Reaction condition: 0.3 g of glucose, 0.1 mmol of catalyst, 2 g of water, 130 C, 120 min. Brønsted acid amount (mmol mmol ). Lewis acid
ꢁ1
d
amount (mmol mmol ). Ref. 17 and 19.
90 min. Aerwards, the solid was separated by an ultraltration
membrane from the aqueous phase and fructose was subse-
ꢀ
quently added. The mixture was heated in water at 130 C for
90 min. The result showed that the conversion efficiency and
yield were 48.9% and 8.9%, respectively. As a control, the
conversion efficiency and yield without using catalyst were
3
48.2% and 8.6%, respectively. Therefore, C16H PW11Cr was
conrmed as a heterogeneous catalyst and the catalytic process
was conrmed as a heterogeneous one.
4. Conclusions
A
dual acidic and water-tolerant heteropolyacid salt
16 3
(C H PW11Cr) has been developed for selective conversion of
fructose and glucose into HMF in the water system. We found
that 30 wt% fructose was converted into HMF with 90.3%
conversion efficiency and a 40.6% yield, and glucose was con-
verted into HMF with 84.2% conversion efficiency and a 35.2%
yield. The high catalytic activity is attributed to the coexistence
of Brønsted and Lewis acid sites in the catalyst and micellar
Fig. 5 The catalyst activity in six reaction cycles. Reaction conditions: 0.6 g of
ꢀ
fructose, 2 g of water, 0.1 mmol of C16
H
3
PW11Cr, 130 C, 90 min.
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structure containing hydrophobic groups. Moreover, this cata- 14 Y. Yang, C.-W. Hu and M. M. Abu-Omar, Green Chem., 2012,
lyst is recyclable and tolerant to high-concentration feedstock, 14, 509–513.
which can decrease the pollution of the Cr atom in real 15 E. A. Pidko, V. Degirmenci and E. J. M. Hensen,
applications.
ChemCatChem, 2012, 4, 1263–1271.
16 B. R. Caes, M. J. Palte and R. T. Raines, Chem. Sci., 2013, 4,
1
96–199.
Acknowledgements
1
7 K. Nakajima, Y. Baba, R. Noma, M. Kitano, J. N. Kondo,
S. Hayashi and M. Hara, J. Am. Chem. Soc., 2011, 133,
4224–4227.
The authors are grateful for the nancial support provided by
the National Natural Science Foundation of China (51078066
and 20871026), as well as the project of Jilin Provincial Science 18 F. Yang, Q. Liu, M. Yue, X. Bai and Y. Du, Chem. Commun.,
and Technology Department (20086035, 20100416, 201105001).
2011, 47, 4469–4471.
1
2
9 F. Yang, Q. Liu, X. Bai and Y. Du, Bioresour. Technol., 2011,
102, 3424–3429.
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