MCM-41 Immobilized Acidic Functional Ionic Liquid and Chromium(III) Complexes Catalyzed Conversion of Hexose into 5-Hydroxymethylfurfural

Article abstract of DOI:10.1002/cjoc.201600912

The development of novel methods to obtain biofuels and chemicals from biomass has been an immediate issue in both academic and industrial communities. In this work, a series of novel catalysts were prepared and characterized by FT-IR, TGA, XRD, SEM, TEM, ICP-AES, NH₃-TPD and BET, which were applied for the conversion of hexose to 5-hydroxymethylfurfural (HMF). The Cr(Salten)-MCM-41-[(CH₂)₃SO₃HVIm]HSO₄ catalyst was the most active catalyst, and a glucose conversion of 99.8% with 50.2% HMF yield was obtained at 140 °C for 4 h in dimethyl sulfoxide (DMSO). The effects of reaction temperature, reaction time, solvents and catalyst dosages were investigated in detail. MCM-41 immobilized acidic functional ionic liquid and chromium(III) Schiff base complexes as heterogeneous catalysts can be easily recovered by simple filter treatment, exhibiting excellent stability and activity towards hexose conversion. Thus the heterogeneous catalysts were environment-friendly for transforming biomass carbohydrates into fine chemicals.

Full text of DOI:10.1002/cjoc.201600912

FULL PAPER
DOI: 10.1002/cjoc.201600912
MCM-41 Immobilized Acidic Functional Ionic Liquid and Chro-
mium(III) Complexes Catalyzed Conversion of Hexose into
5-Hydroxymethylfurfural
Wenwen Yuan,a Yi Huang,a Chunyan Wu,a Xiang Liu,a Yongmei Xia,b and Haijun Wang*,a
a School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China
b State Key Laboratory of Food Science & Technology, Wuxi, Jiangsu 214122, China
The development of novel methods to obtain biofuels and chemicals from biomass has been an immediate issue
in both academic and industrial communities. In this work, a series of novel catalysts were prepared and character-
ized by FT-IR, TGA, XRD, SEM, TEM, ICP-AES, NH3-TPD and BET, which were applied for the conversion of
hexose to 5-hydroxymethylfurfural (HMF). The Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4 catalyst was the
most active catalyst, and a glucose conversion of 99.8% with 50.2% HMF yield was obtained at 140 ℃ for 4 h in
dimethyl sulfoxide (DMSO). The effects of reaction temperature, reaction time, solvents and catalyst dosages were
investigated in detail. MCM-41 immobilized acidic functional ionic liquid and chromium(III) Schiff base complex-
es as heterogeneous catalysts can be easily recovered by simple filter treatment, exhibiting excellent stability and
activity towards hexose conversion. Thus the heterogeneous catalysts were environment-friendly for transforming
biomass carbohydrates into fine chemicals.
Keywords glucose, chromium(III) schiff base complex, acidic ionic liquid, MCM-41, 5-hydroxymethylfurfural
Introduction
HMF.[10] Therefore, the efficient and economical con-
version of carbohydrates to HMF is important for the
biomass utilization. Conventionally, HMF is produced
by dehydration of monosaccharides (e.g. glucose and
fructose), disaccharides (e.g. sucrose and maltose) and
polysaccharides (e.g. starch and cellulose) in an acidic
medium.[11] So far, the transformations of glucose and
fructose into HMF have attracted much attention in
monosaccharide. Though a high yield of HMF is ob-
tained using fructose as feedstock, the large-scale ap-
plication of this process is restricted due to the limited
sources and high price of fructose.[12] Compared with
fructose, glucose is the more abundant and inexpensive
monosaccharide in nature.[13]
The depletion of fossil energy and global climate
change contributes to more and more attention on the
development and utilization of renewable sources to
produced fuels and chemicals.[1] As a widely distributed,
hugely produced, renewable, and low-pollution resource
and potential application values, biomass can be not
only used as fuel, but also converted into chemical in-
termediates for the production of various chemicals and
liquid fuels, such as 5-hydroxymethylfurfural (HMF) and
lactic acid.[2] HMF, called a ‘sleeping giant’ as a versa-
tile intermediate, is an important and valuable platform
compound.[3,4,5]
HMF is an important and versatile platform chemical
that can be further converted into more than 175 valua-
ble bio-based products as fine chemicals, polymeric
materials, pharmaceuticals and liquid fuels.[6,7] Selective
oxidation of HMF can generate an important chemical,
2,5-furandicarboxylic acid (FDCA). FDCA can replace
the petrochemical derived terephthalic acid, a building
block for the synthesis of polymers.[8] 2,5-Dimethyl-
furanis produced by hydrogenation of HMF, can be used
as an additive in automotive liquid biofuels.[9]
1-Hydroxyhexane-2,5-dione as a new platform com-
pound can also be produced by hydrogenation of
HMF production from glucose mainly comprises
two steps, namely, isomerization of glucose to fructose
and dehydration of fructose to HMF.[14,15] Lewis acid
can promote the isomerization process of glucose, and
Brønsted acid can catalyze the dehydration process.
Thus, it is vitally important to combine a Lewis acid and
a Brønsted acid for the catalytic conversion of glucose
to HMF. In recent decades, many kinds of catalysts have
been applied to the degradation of glucose. Significant
improvements on glucose conversion to HMF can be
attained by performing the reaction in the presence of a
series of metal halide (such as CrCl3, SnCl4, CrCl2 and
*
E-mail: wanghj329@outlook.com; Tel.: 0086-13382888162; Fax: 0086-0510-89880685
Received December 27, 2016; accepted March 6, 2017; published online XXXX, 2017.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201600912 or from the author.
Chin. J. Chem. 2017, XX, 1—10
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Yuan et al.
FULL PAPER
AlCl3),[15,16] which can catalyze the isomerization of
glucose to fructose in tandem with mineral acids.[16] The
effect of different ionic liquids (ILs) on HMF prepara-
tion from glucose in N,N-dimethylacetamide (DMA)
over AlCl3 was revealed by a combined experimental
and computational study. Yang et al.[17] found that ionic
liquids with the same cation but different anions have
different effects on glucose conversion. A series of ce-
rous phosphate (CP) catalysts with different crystal
structures for the dehydration of glucose into HMF were
also studied. Cerous phosphate (CP) was synthesized by
a hydrothermal method at 120 ℃, which has a hexago-
nal crystal structure and obtains 97% conversion of
glucose and 61% yield of HMF.[18] Wang et al.[19] used
AlCl3 as catalyst, water and 1,2-dimethoxyethane
(DMOE) as solvent under optimal conditions, obtaining
a high HMF yield (58.56%). Ordomsky et al.[20] studied
the glucose dehydration over different metal phosphates,
obtaining selectivity towards HMF varying between
30% and 60%, depending on the Lewis to Brønsted
(L/B) acid sites ratio. Chinnappan et al.[21] used pyri-
dinium based dicationic ionic liquid as solvent and
CrCl2 as catalyst to convert glucose into HMF. HMF
yield of 47% was obtained from glucose in the presence
of metal chloride (2.1 mol% CrCl2) at 110 ℃ for 120
min. Despite these homogeneous catalysts and ionic
liquids showing high catalytic efficiency, the challenges
in the catalyst recycling, separation and the expensive
price of ionic liquids greatly reduced their potential in
the commercial viability.[22] To tackle these problems,
heterogeneous catalysts have been widely applied to the
conversion of glucose into HMF. For example,
phosphated TiO2 was examined for the conversion of
glucose to produce HMF, and 90% yield of HMF was
obtained in a water-THF biphasic system containing
N-methyl-2-pyrrolidone (NMP) at 175 ℃.[23] Su et
al.[24] used sulfonic acid functionalized metal-organic
framework MIL-101(Cr)-SO3H as the catalyst for
γ-valerolactone-mediated cascade reaction of glucose
dehydration into HMF, giving an HMF yield of 44.9%
and selectivity of 45.8% under the optimal reaction
conditions. Moreno-Recio et al.[25] utilized thermal or
ion-exchange treatment modified commercial NH4-
ZSM-5 zeolite (MFI) as the catalyst, biphasic NaCl (20
wt%) aqueous solution/methyl isobutyl ketone (MIBK)
system as solvent, achieving 80% conversion of glucose
and 42% yield of HMF at 195 ℃. As seen in the above
mentioned studies, heterogeneous catalysts combining
Lewis with Brønsted acidic sites are favored because
they can effectively catalyze isomerization and dehydra-
tion glucose into HMF.
tures.[27,28] Various transition metal complexes have
been synthesized because of various applications such
as oxidation of alcohol and thiols,[29,30] epoxidation of
olefins,[29] Suzuki-Miyaura coupling reaction,[31] asym-
metric reaction,[32] and so on. Transition metal Schiff
base complexes as homogeneous catalysts in chemical
reactions are greatly limited due to high cost of recovery
and lack of reusability. Nikoorazm et al.[33] have re-
ported that chromium and manganese Schiff base com-
plexes were immobilized on the walls of mesoporous
MCM-41 to overcome the disadvantages of homogene-
ous catalyst. Ghorbani-Choghamarani et al.[34] prepared
a stable, efficient and recoverable heterogeneous nano-
catalyst by immobilizing Ni, Co, Cr, Zn or Cd com-
plexes on Fe3O4 magnetic nanoparticles (M-Salen-
MNPs), which can oxidize sulfides to sulfoxides and
oxidize coupling thiols into their corresponding disul-
fides. Among the above-mentioned support materials,
mesoporous silica MCM-41 has been employed as a
useful and versatile solid support for preparation of het-
erogeneous catalysts due to its large tunable pore di-
mensions, high surface area, and ease of surface func-
tionalization.[35] Therefore, we first synthesized
MCM-41 whose surface was introduced the mercapto-
propyl, leading to a homogeneous distribution of mer-
capto-organic moieties in the silica framework. Then
wang et al.[36] introduced a catalyst by immobilizing
Schiff base chromium complexes on the functionalized
MCM-41, which can catalyze the isomerization of glu-
cose to fructose with high activity and selectivity.
Here we made efforts to explore the immobilization
of chromium(III) Schiff-base moiety and Brønsted
acidic ionic liquid [(CH2)3SO3HVIm]HSO4 on MCM-41.
The bifunctional heterogeneous catalysts can decrease
chromium(III) toxicity and reduce harm to the environ-
ment. In this paper, we reported Cr(Salten)-MCM-41-
[(CH2)3SO3HVIm]HSO4 showed an excellent catalytic
activity for conversion of glucose and could also be
used for the hydrolysis of other carbohydrates, such as
fructose, galactose and inulin.
Experimental
Materials
Salicylaldehyde, chromium acetate (Cr(OAc)3, 99%),
3-aminopropyltrimethoxysilane, 3-mercaptopropyl tri-
methoxysilane, vinylimidazole and 1,3-propanesultone
were purchased from Shanghai Aladdin Industrial Inc.
HMF used in the study was obtained from Sigma-
Aldrich Co. LLC.; inulin was obtained from Alfa Aesar;
fructose, mannose, glucose, cellobiose, cetyltrime-
thylammonium bromide (CTAB), tetraethyl orthosilicate
(TEOS), and o-phenylenediamine were purchased from
Sinopharm Chemical Reagent Co. Ltd. All the chemi-
cals were used without further purification. Deionized
water was produced by using a laboratory water-purifi-
cation system (RO DI Digital plus).
Schiff bases have drawn much attention because
they contain electron-donating group (C＝N), which
can be coordinated with a number of metal ions.[26]
Transition metal Schiff base complex catalysts have
attracted wide attention for their more accessible syn-
thesis conditions and versatile coordination struc-
2
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Chin. J. Chem. 2017, XX, 1—10

Conversion of Hexose into 5-Hydroxymethylfurfural
Preparation of the catalyst
Brønsted acidic ionic liquid ([(CH2)3SO3HVIm]-
HSO4, 3.1 g) and mercaptopropyl modified MCM-41
(MCM-41-SH, 2.0 g) were sequentially added to the
solvent of acetonitrile (30 mL), anhydrous ethanol (20
mL) and the initiator of azobisisobutyronitrile (AIBN,
0.4 g) in a 100 mL round bottom flask.[35] The mixture
was refluxed for 30 h at 80 ℃ under nitrogen atmos-
phere. The product was filtered, subsequently washed
with acetone, ether and ethanol. Finally, the formed sol-
id was dried in vacuum at 60 ℃ for 6 h.
Synthesis of MCM-41 modified with 3-mercapto-
propyl trimethoxysilane (MPS) Mesoporous MCM-
41 was prepared according to the literature method, with
a
slight modification.[26] Post synthesis calcined
MCM-41 (1 g) and 3-mercaptopropyl trimethoxysilane
(6 mL) were added to a 100 mL three-necked flask
charged with ethanol (50 mL) at 70 ℃ for 12 h under
nitrogen atmosphere.[37] The resulting white solid of
functionalized MCM-41 (MCM-41-SH) was filtered,
washed with ethanol, and dried under vacuum.
Scheme 1 The preparation of MCM-41-[(CH2)3SO3HVIm]-
Preparation of MCM-41-[(CH2)3SO3HVIm]HSO4
The acidic ionic liquid [(CH2)3SO3HVIm]HSO4 was
synthesized by the following process.[38] First, 1,3-pro-
pane-sultone (6.1 g) was slowly added to 1-vinylimid-
azole (4.7 g) and ethyl acetate (50 mL) in a 100 mL
three-necked flask at 0 ℃. After completion of the drop,
the mixture was stirred at room temperature for 24 h and
completely turned into solid. Then the formed solid was
washed with ethyl acetate 3 times and dried in vacuum
at 90 ℃ for 2 h. Then, the formed solid (1-vinyl-3-
(3-propyl-sulfonic acid) salt of imidazole intermediate)
was dissolved in 2.5 mL H2O in a 100 mL round bottom
flask, and equal-molar sulfuric acid (2.7 mL) was slowly
dropped into the flask at 0 ℃. After the dropping was
finished, the mixture was heated up to 60 ℃ gradually
and then stirred for 24 h. Finally, the formed brown
viscous liquid was dried in vacuum at room temperature
for 5 h.
HSO4
O
N
SO3H
HN
+
O
O
Si
SH
-
HSO4
O
AIBN/Acetonitrile
reflux, 30 h
SO3H
HN
N
O
O
Si
S
-
HSO4
Preparation of ligand-metal complexes
The ligands were prepared and purified according to
the literature.[36] Further characterization of crystalline
1
ligand was done with the help of FT-IR, H NMR and
UV-vis (see ESI). The chromium(III) complexes were
prepared essentially as described.[36] Complexation of
Scheme 2 Synthetic route of heterogeneous catalyst
SO3H
N
N
N
-
O
O
O
N
Cr
HSO4
N
N
O
O
Toluene acetonitrile
Reflux
N
N
Si
SO3H
-
Cr
S
+
NH2
O
O
HSO4
NH
S
Si
Si
O
Si
OEt
EtO
OEt
OO
O
O
O
1
SO3H
N
N
H
N
-
H
N
HSO4
N
N
O
N
N
Cr
N
N
O Si
O
SO3H
Toluene acetonitrile
Reflux
Cr
S
S
O
O
-
+
HSO4
NH2
O
O
NH2
Si
Si
O O
O
O O
O
Si
OEt
EtO
OEt
2
Chin. J. Chem. 2017, XX, 1—10
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Yuan et al.
FULL PAPER
salphen/Salten with Cr(OAc)3 was carried out by
refluxing them at a 1∶2 molar ratio with continuous
stirring in methanol for 10 h under nitrogen protection.
The obtained solid products were washed with water
and dried under vacuum at 40 ℃. The chromium(III)
complexes were characterized by FT-IR (ESI Figure
S4).
Immobilization of Cr(salphen)/Cr(salten)-APTES
on MCM-41-[(CH2)3SO3HVIm]HSO4 Typically, the
heterogeneous catalyst was synthesized by the following
process.[36,38] The suspension of freshly dried MCM-41-
[(CH2)3SO3HVIm]HSO4 (1.0 g) was dissolved in the
mixture solvent of dry toluene (30 mL) and acetonitrile
(20 mL), the as-prepared Cr(salphen)/Cr(salten)-APTES
(1.0 g, compound 1/2) was added to the mixture and
refluxed for 24 h under N2 atmosphere. The collected
powder was washed overnight in a Soxhlet extractor
using equivalent alcohol and acetonitrile as solvent and
then the solid was dried at 80 ℃ overnight. By choos-
ing in turn the different double amines [Cr(salphen),
Cr(salten)], the corresponding complex-immobilized
materials were obtained and denoted as Cr(salphen)-
MCM-41-[(CH2)3SO3HVIm]HSO4, Cr(salten)-MCM-
41-[(CH2)3SO3HVIm]HSO4, respectively.
Results and Discussion
Catalyst characterization
Infrared spectroscopy was used as a key method to
characterize the functional groups of the products (Fig-
ure 1). FT-IR spectra were recorded on a Nicolet 360
FT-IR instrument (KBr discs) in the 4000－500 cm1
region. ESI Figure S3 shows the UV-Vis diffuse-reflec-
tance spectra of the samples. UV-vis spectra were rec-
orded on TU-1901 dual-beam UV-Vis spectrophotome-
1
ter in the 200－600 nm. H NMR spectra were meas-
ured on a Bruker DPX 300 spectrometer at ambient
temperature in CDCl3 using TMS as the internal refer-
ence. Thermo gravimetric analysis (TGA, STA409) was
determined from 50 to 600 ℃ using a ramp rate of
20 ℃/min. The synthesized samples were examined by
X-ray diffraction (XRD) using a Bruker D8 Advance
powder diffractometer. The Ni-filtered Cu/Kα radiation
was used at an acceleration voltage of 40 kV and a cur-
rent of 20 mA with a scanning speed of 1 (°)/min. The
diffraction angle was scanned from 1° to 10°. The tex-
tural properties of the mesoporous materials were
measured using the Brunauer-Emmett-Teller (BET)
method over the range p/p0＝0.05－0.30, where a linear
relationship was maintained. Pore size distributions
were calculated using the Barrett-Joyner-Halenda (BJH)
model. TEM studies were performed on a JEOL JEM
model 2100 microscope operated at 200 kV. SEM stud-
ies were carried on a HITACHI S-4800 field-emission
scanning electron microscope. NH3-TPD was conducted
with an AutoChem 5080 chemisorption analyzer.
Catalytic reactions
The hexose dehydration reaction experiments were
carried out in a 25 mL reaction vial equipped with a
magnetic stirrer. The typical experiment for hexose de-
hydration was as follows: hexose (100 mg), catalyst (50
mg) and DMSO (2 mL) were added into the reaction
vial. The reaction mixture was heated to desirable tem-
peratures for a specific time. After the reaction was run
for the desired time, the products were filtered out of the
catalyst and then diluted with deionized water, and ana-
lyzed using a high-performance liquid chromatography
(HPLC).
Analysis
The liquid samples were analyzed with HPLC using
an Agilent Alliance System instrument (1100 Series)
equipped with a refractive index detector and a Shodex
SURGER SP0810 (300×8.0) column for analysis. Ul-
tra-pure water was used as the mobile phase, with a
flow rate of 0.7 mL/min and 70 column temperature.
The concentrations of glucose, fructose, and HMF were
quantified by HPLC analysis through the external
standard method and calibration curves of commercially
available standard substrates. Glucose conversion (conv.
mol%) and HMF yield (mol%) were calculated accord-
ing to:
Figure 1 FT-IR spectrum of Cr(Salphen)-MCM-41-[(CH2)3-
SO3HVIm]HSO4.
SEM and TEM analysis
The SEM micrographs of the pure MCM-41 and the
Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4
are
shown in Figures 2(I) and 2(II). Pure MCM-41
exhibited spherical particles with uniform size and
diameter at the nano level, the surface of the catalyst
generated aggregation when organic functional groups
were supported on it (Figure 2(II)). As seen from the
Figure 2(III), the TEM micrograph confirms that the
material presents longer range order, dimensional pores,
Glucose conversion (mol%)＝
moles of remaining glucose
(1－
)100%
×100%
starting moles of glucose
moles of HMF
HMF yield (mol%)＝
starting moles of glucose
4
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Conversion of Hexose into 5-Hydroxymethylfurfural
similar to the pure silicon MCM-41. The image of the
catalyst Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4
was showed in ESI Figure S8.
ous catalyst were similar to that of the homogeneous
Cr(salphen) complex, indicating that the quadridentate
coordination structure of homogeneous complex
(Cr(salphen)) remained intact in all immobilized com-
plexes. The FT-IR spectrum of Cr(salten)-MCM-41-
[(CH2)3SO3HVIm]HSO4 was showed in ESI Figure
S5(II).
Small angle X-ray diffraction studies
The powder XRD patterns of MCM-41, Cr(Sal-
phen)-MCM-41-[(CH2)3SO3HVIm]HSO4 and Cr(Sal-
ten)-MCM-41-[(CH2)3SO3HVIm]HSO4 are all showed
in Figure 3 (I and II). The (b) and (c) of Figure 3 indi-
cated that the structural ordering of the com-
plex-immobilized materials remains intact. In the XRD
pattern (Figure 3) of pure MCM-41, a very strong
reflection at 2θ＝1.89° for d100 and also two other
weaker reflections at 2θ＝3.79° and 4.35° for d110 and
d200, respectively, can be indexed to well-ordered
mesoporous material of a hexagonal symmetry.[41] After
immobilization of Cr complex, the intensity of the peak
at (100) decreased largely, the higher angle peaks in the
parent sample no longer appeared. It is mainly due to a
loss of the mesoporous order. Nevertheless, the immobi-
lized catalyst remains structural ordering of the
MCM-41 channels. After being recycled five times the
catalysts remain ordering structure of the MCM-41
channel.
Figure 2 (I) SEM image of the pure MCM-41, (II) SEM image
of the catalyst Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4,
(III) TEM image of the catalyst Cr(Salphen)-MCM-41-
[(CH2)3SO3HVIm]HSO4.
FT-IR spectroscopy
The FT-IR spectrum of heterogeneous catalyst
Cr(salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4 showed
the characteristic bands at 1611, 1532, 1459, 1189, 1123,
1042, 760 and 616 cm–1 (Figure 1), which fit well with
the published data in literature.[39] The representative
bands for a tetradentate ONNO functionality appeared
at about 1611 cm–1, which were attributed to the C＝N
stretching vibration of imine groups and were shifted to
a lower frequency (1610 cm–1) on complexation. The
representative bands at 1459 and 1532 cm1 were due to
C＝N and C＝C vibrations of the imidazole ring. The
vibration at 1042 cm1 was attributed to Si-O-Si asymmet-
ric stretching vibration peaks, indicating that the complex
had been immobilized onto the functionalized silica.[40] If
the bands belonging to MCM-41-[(CH2)3SO3HVIm]-
HSO4 were excluded, the FTIR spectra of heterogene-
Figure 3 Low angle powder XRD patterns of MCM-41 (a),
Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4 (b) and Cr(Salten)-
MCM-41-[(CH2)3SO3HVIm]HSO4 (c), and the catalyst recycled
five times of Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4 (b')
and Cr(Salten)-MCM-41-[(CH2)3-SO3HVIm]HSO4 (c').
Chin. J. Chem. 2017, XX, 1—10
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Yuan et al.
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N2 sorption studies
The initial weight loss (＜1.2%) from the samples
(＜150 ℃) is due to the removal of physically adsorbed
water and non-bonded surface hydroxyl group. The
weight loss (1.2%－4.1%) between 200 and 250 ℃ is
attributed mainly to the removal of chemically adsorbed
water. Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4
presents a loss of about 38.2% (Cr(Salphen)-MCM-41-
[(CH2)3SO3HVIm]HSO4, 37.9%) at 250 －550 ℃,
which is attributed to the loss of the acid ionic liquid
and chromium complex covalently grafted onto the sili-
ca. On the basis of these results, the supported catalyst
exhibited good thermal stability below 250 ℃.
The N2 adsorption-desorption isotherms of MCM-41
and immobilized complexes are showed in Figure 4 (I
and II). MCM-41 gives typical type IV adsorption iso-
therms with H1 hysteresis loop according to IUPAC
classification, indicating the presence of the mesoporosity.
The H1 hysteresis loop was related to the capillary con-
densation in the mesopore channels.[42] The textural prop-
erties of initial support and supported Cr-salphen/salten
samples are given in Table 1, which demonstrate that
the surfaces have substantially changed over the organic
functionalized group and Cr-salphen/salten complexes.
Noticeably, for the immobilized complexes, the surface
area decreased in the samples, which indicated that
Cr-salphen/salten complexes had entered into the pore
channel of zeolite instead of adsorbing on the support
external surface. Most likely some pores were blocked
by the aminopropyl and acid ionic liquid.[41] But the
average pore diameters decreased in the samples, which
suggested that acid ionic liquids and the Cr-salphen/
salten complexes may be well confined in the pores of
mesoporous silica.
Figure
5
TG analysis for the Cr(Salphen)-MCM-41-
[(CH2)3SO3HVIm]HSO4 (a) and Cr(Salten)-MCM-41-[(CH2)3-
SO3HVIm] HSO4 (b), and the recovered catalyst after five runs of
Cr(Salphen)MCM-41-[(CH2)3SO3HVIm]HSO4 (c) and Cr(Salten)-
MCM-41-[(CH2)3SO3HVIm]HSO4 (d).
Conversion of glucose to HMF by different catalysts
According to previous experimental data,[36] ob-
tained Cu and Mn Schiff base complexes had little cat-
alytic activity for the dehydration of glucose. But Cr
Schiff base complexes can efficiently catalyze the
isomerization of glucose to fructose under certain con-
ditions. HMF production from glucose is still a chal-
lenge compared to that from fructose. Insights into the
most preferred mechanistic pathways for isomerization
of glucopyranose to fructofuranose and subsequent de-
hydration of fructofuranose to the final product HMF,
were considered to be two main reactions in the whole
process.[43] Chromium(III) Schiff base complexes im-
mobilized on modified MCM-41 can be more active for
the isomerization of glucose into fructose (Table 2, En-
tries 4－11). Based on the results discussed above, ionic
liquid modified MCM-41 is a good heterogeneous sup-
port (Table 2, Entries 10, 11).
Figure 4 Nitrogen adsorption-desorption isotherms of MCM-
41 (a), Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4 (b) and
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4 (c).
The yield of HMF was the highest among these cat-
alysts (Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4,
50.2%, Figure 6), indicating that the Brønsted acidic
functionality is an important factor for HMF selectivity.
Based on the results discussed above, Schiff base chro-
mium complexes immobilized on ionic liquid modified
mesoporous materials exhibit more excellent catalytic
activity toward the dehydration of glucose.
Thermal analysis
TG analysis was performed to determine percent
weight loss of the samples. TG graphs of supported
Cr-salphen/salten complex were showed in Figure 5.
6
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Conversion of Hexose into 5-Hydroxymethylfurfural
deactivation at low temperatures.[44] However, the cata-
lytic results reflect that HMF yield rose with increase of
temperature and time at first, achieving a value close to
47.4% (Figure 7(I)) and 50.2% (Figure 7(II)) at 140 ℃.
The main reason was that the isomerization and dehy-
dration reactions of glucose were accelerated by in-
creasing the temperature, which was favorable to
achieve a high yield. The HMF yield decreased from 4 h
to 5 h, which can be explained by that the transfor-
mation of glucose was limited because some acidic sites
were covered by the rapidly formed humus on the sur-
face of catalyst.[45] As is shown in Figure 7, both too
high temperature and too long time were not conducive
to the stability of HMF due to the side reaction. From
these data, 140 ℃ and 4 h were selected as the opti-
mum conditions to study other parameters of the cata-
lytic process.
Figure 6 Influence of different catalysts on the conversion of
glucose to HMF. Reaction conditions: 100 mg of glucose, 2 mL
of DMSO, 50 mg of catalyst, 140 ℃.
Catalytic conversion of glucose into HMF at differ-
ent reaction temperatures
Catalytic conversion of glucose into HMF with dif-
ferent amount of catalyst
Different temperatures and reaction times were in-
vestigated to achieve maximum yield of HMF from
glucose when DMSO was used as solvent. The reaction
time is from 1 to 5 h at different temperatures (120, 130,
140, 150 ℃). As shown in Figures 7(I), (II), when the
reaction temperatures were lower than 140 ℃, with the
elongation of reaction time, the catalytic efficiency of
glucose into HMF was still not high, the HMF yield did
not improve significantly. The probable reason may be
that the substrates or products were strongly adsorbed
on the surface of mesoporous silica materials causing
Next, the influence of different dosages of catalyst
on the conversion of glucose at 140 ℃ for 4 h was
evaluated in Figure 8. The variations of the catalyst
dosage (30－70 mg) show that the glucose conversion
slightly improved with the increasing of catalyst dosag-
es, possibly as a consequence of the catalyst having
more active sites on conversion of glucose in DMSO
(Figure 8). However, further increase in catalyst dosages
decreased the HMF yield. It means that the excessive
Table
1
Physico-chemical properties of MCM-41, Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4 and Cr(Salten)-MCM-41-
[(CH2)3SO3HVIm]HSO4
Average
pore
size/nm
6.74
Surface
aciditya/
(mmol•g1)
－
Crb/
wt%
Surface area/
(m2•g1)
Pore volume/
(cm3•g1)
Entry
1
2
3
Sample type
MCM-41
Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4
Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4
749.4
473.2
479.0
469.8
1.264
0.605
－
1.98
2.01
5.10
0.132
0.800
0.592
0.790
6.68
5.04
6.64
0.141
0.126
0.133
c
4
5
1.84
1.96
d
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4
475.9
a
b
Acid concentration values were determined through NH3-TPD. The chromium contents of the catalysts were detected by using
ICP-AES. c,d The recovered catalyst after five runs.
Table 2 The catalytic activity of different catalysts on the conversion of glucose into HMFa
Entry
Catalyst
Temperature/℃
130 (glucose)
130 (glucose)
130 (glucose)
140 (glucose)
140 (glucose)
140 (glucose)
140 (glucose)
140 (glucose)
140 (glucose)
140 (glucose)
140 (glucose)
Time/h
HMF yield/%
19.9
13.8
16.3
29.4
38.9
36.4
29.8
40.1
1
2
3
4
5
6
7
8
MCM-41-[(CH2)3SO3HVIm]HSO4
Cr(salphen)
Cr(salten)
4
4
5
4
4
4
5
4
4
4
4
Cr(salphen)-MCM-41
Cr(salphen)-MCM-41-SH
Cr(salphen)-MCM-41-SO3H
Cr(salten)-MCM-41
Cr(salten)-MCM-41-SH
Cr(salten)-MCM-41-SO3H
Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4
9
10
11
39.6
47.5
50.2
a Reaction conditions: 100 mg gluctose, 2 mL DMSO, 50 mg catalyst.
Chin. J. Chem. 2017, XX, 1—10
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7

Yuan et al.
FULL PAPER
catalyst has not facilitated the transformation of glucose
into HMF due to the formation of undesired products
such as soluble polymers and humins. Thus the optimal
dosage of catalyst for the reaction is 50 mg.
Catalytic conversion of glucose into HMF over dif-
ferent solvents
It is known that the solvent is an important factor,
which affects the reaction efficiency. Thus, we have
investigated the catalytic activity of Cr(Salten)-MCM-
41-[(CH2)3SO3HVIm]HSO4 in a variety of common
solvents at 140 ℃ for 4 h (Table 3). It is noted that the
solvent showed a remarkable effect on both glucose
conversion and HMF yield. The reaction in DMA gave a
poor HMF yield of 12.1% (Table 3, Entry 3). 50.2%
HMF yield was obtained in the strong polar and
high-boiling-point solvent (DMSO; Table 3, Entry 4),
because DMSO favors the furanoid form and the side
reactions are remarkably suppressed.[45] Clearly, DMA,
DMF and NMP were less effective as reaction media in
the study. When NMP was used as solvent, the yield of
HMF reached 31.1% with 97.9% fructose conversion. In
addition, the catalytic activity of Cr(Salten)-MCM-41-
[(CH2)3SO3HVIm]HSO4 can be further verified for glu-
cose conversion in a biphasic system (H2O/DMSO and
[AMIM]Cl/DMSO). It was demonstrated that DMSO
with the co-solvent of [AMIM]Cl in different propor-
tions can obtain various yield of HMF (37.8%－43.3%).
One possible reason for this is that the IL may simulta-
neously play the role of a solvent, stabilize the HMF
product in the reaction mixture and increase the reaction
selectivity.[46]
Figure 7 Glucose transformation into HMF in the presence of
Cr(Salphen)-MCM-41-[(CH2)3SO3HVIm]HSO4(I) and Cr-
(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4(II). Reaction condi-
tions: 100 mg glucose, 2 mL DMSO, 50 mg catalyst.
Further experiments demonstrate that co-solvent
plays an important role in the conversion of glucose into
HMF. For example, the yield of HMF in a biphasic sys-
tem (DMSO/H2O) is 36.8% (Table 3, Entry 8). The ex-
planation for this trend is that a small amount of water
could lower the viscosity of reaction system and then
promote the mass transfer between catalyst and glucose,
which helps the hydrolysis of glucose.[46] In addition, in
aqueous solution, the resulting HMF simultaneously
combines with water to produce levulinic acid and for-
mic acid, reducing the yield of HMF.
Recyclability of the catalysts
The recyclability is of great importance for applying
a catalyst in industrial process. Therefore, we chose
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4 as a cat-
alyst to research the recyclability for the dehydration
reaction of glucose (Figure 9), maintaining the same
reaction conditions as those described above, except
using a recovered catalyst. After the reactions, the cata-
lyst was separated by filtration from the reaction mix-
ture. The recovered catalyst was washed with water and
ethanol and dried at 60 ℃ overnight, prior to its reuse
in another run. As depicted in Figure 9, no obvious de-
crease in catalytic activity was observed after five suc-
cessive reaction runs, suggesting that Cr(Salten)-
Figure 8 The HMF yield and conversion of glucose with dif-
ferent amounts of catalyst. Cr(Salphen)-MCM-41-[(CH2)3SO3-
HVIm]HSO4 (I) and Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]-
HSO4 (II). Reaction conditions: 100 mg glucose, 2 mL DMSO,
140 ℃, 4 h.
8
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Chin. J. Chem. 2017, XX, 1—10

Conversion of Hexose into 5-Hydroxymethylfurfural
Table 3 Effect of solvents on the conversion of glucose into HMFa
Entry
Solvent
Temperature/℃
Conversion/%
99.8
HMF yield/%
50.2
1
2
DMSO (Dimethyl sulfoxide)
DMF (N,N-Dimethylformamide)
DMA (N,N-Dimethylacetamide)
NMP (N-Methyl pyrrolidone)
[AMIM]Cl(0.5)＋DMSO(1.5)
[AMIM]Cl(1)＋DMSO(1)
[AMIM]Cl(1.5)＋DMSO(0.5)
H2O(0.5)＋DMSO(1.5)
H2O(1)＋DMSO(1)
140
140
140
140
140
140
140
140
140
140
89.1
16.5
3
80.1
12.1
4
97.9
31.1
5
98.9
37.8
6
99.1
43.3
7
99.2
41.5
8
88.4
36.8
9
82.1
27.9
10
H2O(1.5)＋DMSO(0.5)
78.6
25.6
a Reaction conditions: 100 mg of glucose, 50 mg of Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4, 2 mL of solvent, 4 h.
Table 4 Dehydration of different substrates catalyzed by
a
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4
Entry Substrate Time/h Temperature/℃
HMF yield/%
1
2
3
4
5
6
Fructose
Sucrose
Mannose
Inulin
Galactose
Cellulose
4
5
4
3
4
5
130
140
140
140
140
140
89.3
82.3
33.7
82.5
13.9
9.2
a Reaction conditions: 100 mg of substrate, 50 mg of catalyst, 2
mL of DMSO.
Figure 9
Reusability of the Cr(Salten)-MCM-41-[(CH2)3-
MCM-41-[(CH2)3SO3HVIm]HSO4 is an efficient cata-
lyst that favors the isomerization of the glucose and the
dehydration of the fructose. Catalytic conversions of
glucose, galactose, cellulose, and sucrose into HMF
have been extensively studied over several combina-
tions of two kinds of catalytic sites. The catalyst
SO3HVIm]HSO4 catalyst in the dehydration of glucose. Reaction
conditions: 50 mg catalyst, 2 mL DMSO,140 ℃, 4 h.
MCM-41-[(CH2)3SO3HVIm]HSO4 exhibited excellent
catalytic stability and recyclability.
Cr(Salten)-MCM-41-[(CH2)3SO3HVIm]HSO4
has
Conversion of other feedstock to HMF
demonstrated to be the most active with high conversion
rate and HMF yield (50.2%) at 140 ℃ for 4 h in
DMSO. Although these processes still need to be im-
proved for practical application, we believe that further
progress will realize the biorefinery by heterogeneous
catalysis to ensure sustainable development.
The reaction conditions of fructose, sucrose, inulin,
mannose, galactose and cellulose dehydration and cor-
responding HMF yields were summarized in Table 4.
89.3% yield of HMF was obtained for the dehydration
of fructose when Cr(Salten)-MCM-41-[(CH2)3SO3-
HVIm]HSO4 was used as a catalyst at 130 ℃ for 4 h
(Table 4, Entry 1). When galactose and cellulose were
subjected to reaction system, the HMF yield was re-
markably inferior (Table 4, Entries 5, 6). This result
clearly indicates that Cr(Salten)-MCM-41-[(CH2)3SO3-
HVIm]HSO4 as bifunctional acidic catalyst can hardly
catalytze the conversion of galactose and cellulose, be-
cause it is difficult for hydrolysis of cellulose and the
isomerization of galactose in the organic media. Among
these results, the catalyst still showed good catalytic
performance in synthesizing HMF.
References
[1] Tong, X.; Yu, L.; Chen, H.; Zhuang, X.; Liao, S.; Cui, H. Catal.
Commun. 2017, 90, 91.
[2] Wang, J.; Qu, T.; Liang, M.; Zhao, Z. RSC Adv. 2015, 5, 106053.
[3] Bozell, J. J.; Petersen, G. R. Green Chem. 2010, 12, 539.
[4] Roman-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Nature
2007, 447, 982.
[5] Li, J.; Ma, Y.; Wang, L.; Song, Z.; Li, H.; Wang, T.; Li, H.; Eli, W.
Catalysts 2015, 6, 1.
[6] Siankevich, S.; Fei, Z.; Yan, N.; Dyson, P. J. Chimia (Aarau) 2015,
69, 592.
[7] Mukherjee, A.; Dumont, M.-J.; Raghavan, V. Biomass Bioenergy
2015, 72, 143.
Conclusions
[8] Zhang, Z.; Zhen, J.; Liu, B.; Lv, K.; Deng, K. Green Chem. 2015, 17,
1308.
[9] Yang, P.; Cui, Q.; Zu, Y.; Liu, X.; Lu, G.; Wang, Y. Catal. Commun.
2015, 66, 55.
In summary, glucose or glucose-based carbohydrates
were efficiently transformed into HMF catalyzed by
functionalized mesoporous silica materials. Cr(Salten)-
Chin. J. Chem. 2017, XX, 1—10
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
9

Yuan et al.
FULL PAPER
[10] Xu, Z.; Yan, P.; Zhang, Z. Chin. J. Org. Chem. 2017, 37, 40.
[11] Zakrzewska, M. E.; Bogel-Łukasik, E.; Bogel-Łukasik, R. Chem.
Rev. 2011, 111, 397.
Inorg. M. 2014, 45, 1300.
[29] Bhunia, S.; Jana, S.; Saha, D.; Dutta, B.; Koner, S. Catal. Sci. Tech-
nol. 2014, 4, 1820.
[12] Li, W.; Xu, Z.; Zhang, T.; Li, G.; Jameel, H.; Chang, H.; Ma, L. Bio-
resour 2016, 11, 5839.
[30] Nikoorazm, M.; Ghorbani-Choghamarani, A.; Noori, N. Res. Chem
Intermed. 2016, 42, 4621.
[13] Yang, Y.; Liu, W.; Wang, N.; Wang, H.; Song, Z.; Li, W. RSC Adv.
2015, 5, 27805.
[31] Dhara, K.; Sarkar, K.; Srimani, D.; Saha, S. K.; Chattopadhyay, P.;
Bhaumik, A. Dalton Trans. 2010, 39, 6395.
[14] van Putten, R.-J.; van der Waal, J. C.; de Jong, E.; Rasrendra, C. B.;
Heeres, H. J.; de Vries, J. G. Chem. Rev. 2013, 113, 1499.
[15] Wang, T.; Nolte, M. W.; Shanks, B. H. Green Chem.2014, 16, 548.
[16] Pagán-Torres, Y. J.; Wang, T.; Gallo, J. M. R.; Shanks, B. H.;
Dumesic, J. A. ACS Catal. 2012, 2, 930.
[17] Yang, Y.; Liu, W.; Wang, N.; Wang, H.; Li, W.; Song, Z. Chin. J.
Chem. 2015, 33, 583.
[18] Wang, L.; Yuan, F.; Niu, X.; Kang, C.; Li, P.; Li, Z.; Zhu, Y. RSC Adv.
2016, 6, 40175.
[19] Wang, S.; Lin, H.; Chen, J.; Zhao, Y.; Ru, B.; Qiu, K.; Zhou, J. RSC
Adv. 2015, 5, 84014.
[20] Ordomsky, V. V.; Sushkevich, V. L.; Schouten, J. C.; vander Schaaf,
J.; Nijhuis, T. A. J. Catal. 2013, 300, 37.
[21] Chinnappan, A.; Jadhav, A. H.; Chung, W.-J.; Kim, H. Ind. Crops
Prod. 2015, 76, 12.
[32] Thakur, S. S.; Chen, S.-W.; Li, W.; Shin, C.-K.; Kim, S.-J.; Koo,
Y.-M.; Kim, G. J. J. Organomet. Chem. 2006, 691, 1862.
[33] Nikoorazm, M.; Ghorbani-Choghamarani, A.; Khanmoradi, M. J.
Porous. Mater. 2016, 23, 761.
[34] Ghorbani-Choghamarani, A.; Darvishnejad, Z.; Tahmasbi, B. Inorg.
Chim. Acta 2015, 435, 223.
[35] Rohitha, C. N.; Kulkarni, S. J.; Narender, N. Synth. Commun. 2013,
43, 2853.
[36] Wang, Y.; Gu, Z.; Liu, W.; Yao, Y.; Wang, H.; Xia, X.-F.; Li, W. RSC
Adv. 2015, 5, 60736.
[37] Qiao, K.; Hagiwara, H.; Yokoyama, C. J. Mol. Catal. A: Chem. 2006,
246, 65.
[38] Miao, J.; Wan, H.; Guan, G. Catal. Commun. 2011, 12, 353.
[39] Wang, X.; Wu, G.; Li, J.; Zhao, N.; Wei, W.; Sun, Y. Catal. Lett.
2007, 119, 87.
[22] Deng, T.; Li, J.; Yang, Q.; Yang, Y.; Lv, G.; Yao, Y.; Qin, L.; Zhao, X.;
Cui, X.; Hou, X. RSC Adv. 2016, 6, 30160.
[40] Wu, G.; Wang, X.; Liu, X.; Ding, K.; Zhang, F.; Zhang, X. Catal.
Lett. 2013, 144, 364.
[23] Atanda, L.; Shrotri, A.; Mukundan, S.; Ma, Q.; Konarova, M.; Bel-
tramini, J. ChemSusChem 2015, 8, 2907.
[41] Yuan, X.; Shan, G.; Li, L.; Wu, J.; Luo, H.-A. Catal. Lett. 2015, 145,
868.
[24] Su, Y.; Chang, G.; Zhang, Z.; Xing, H.; Su, B.; Yang, Q.; Ren, Q.;
Yang, Y.; Bao, Z. AIChE J. 2016, 62, 4403.
[25] Moreno-Recio, M.; Santamaría-González, J.; Maireles-Torres, P.
Chem. Eng. J. 2016, 303, 22.
[26] Narang, S.; Mehta, R.; Upadhyay, S. N. Ind. Eng. Chem. Res. 2013,
52, 3967.
[27] Yaul, R.; Dhande, V.; Pethe, B.; Aswar, S. Bull. Chem. Soc. Ethiop.
2014, 28, 255.
[42] Liou, T.-H. Chem. Eng. J. 2011, 171, 1458.
[43] Guan, J.; Cao, Q.; Guo, X.; Mu, X. Comput. Theor. Chem. 2011, 963,
453.
[44] Yi, X.; Delidovich, I.; Sun, Z.; Wang, S.; Wang, X.; Palkovits, R.
Catal. Sci. Technol. 2015, 5, 2496.
[45] Zhang, Z.; Du, B.; Zhang, L.-J.; Da, Y.-X.; Quan, Z.-J.; Yang, L.-J.;
Wang, X.-C. RSC Adv. 2013, 3, 9201.
[46] Zhang, Z.; Du, B.; Quan, Z.-J.; Da, Y.-X.; Wang, X.-C. Catal. Sci.
Technol. 2014, 4, 633.
[28] Refat, M. S.; El-Megharbel, S. M.; Adam, A. M. A. Synth. React.
(Lu, Y.)
10
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