Efficient conversion of glucose to 5-hydroxymethylfurfural using bifunctional partially hydroxylated AlF3

Article abstract of DOI:10.1039/c5ra24013a

Partially hydroxylated AlF₃ (denoted as AlF₃) was synthesized by using a sol-gel method, and unambiguously characterized by FT-IR, XRD, NH₃-TPD, SEM, TEM, N₂ adsorption-desorption, and FTIR (pyridine-adsorption) techniques. The resulting mesoporous material (AlF₃) simultaneously bearing Lewis and Br?nsted acid sites was efficient for producing 5-hydroxymethylfurfural (HMF) from glucose, and an optimized HMF yield of 57.3% at a glucose conversion of 95.5% was obtained within 10 h at 140 °C. The effects of reaction temperature, time, catalyst amount, solvent and substrate type, and the amount of Br?nsted/Lewis acid sites on conversion of glucose to HMF were also investigated. The existence of both Lewis and Br?nsted acid sites in AlF₃ was found to play a key role in glucose-to-HMF conversion.

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Efficient conversion of glucose to 5-hydroxymethylfurfural by
using bifunctional partially hydroxylated AlF3
Received 00th January 20xx,
Accepted 00th January 20xx
Ye-Min Lu, Hu Li, Jian He, Yan-Xiu Liu, Zhi-Bing Wu, De-Yu Hu and Song Yang*
DOI: 10.1039/x0xx00000x
Partially hydroxylated AlF
by FT-IR, XRD, NH -TPD, SEM, TEM, N
mesoporous material (AlF ) simultaneously bearing Lewis and Brønsted acid sites was efficient for producing 5-
3
(denoted as AlF
3
) was synthesized by using a sol–gel method, and unambiguously characterized
www.rsc.org/
3
2
adsorption-desorption, and FTIR (pyridine-adsorption) techniques. The resulting
3
hydroxymethylfurfural (HMF) from glucose, and an optimized HMF yield of 57.3% at glucose conversion of 95.5% was
obtained within 10 h at 140 ºC. The effects of reaction temperature, time, catalyst amount, solvent and substrate type,
and the amount of Brønsted/Lewis acid sites on converrsion of glucose to HMF were also investigated. The existence of
3
both Lewis and Brønsted acid sites in AlF was found to play a key role in glucose-to-HMF conversion.
2
0
recyclable. In general, catalytic conversion of glucose to HMF
through two steps including glucose-to-fructose isomerization and
subsequent dehydration to produce HMF, in which Lewis acid sites
facilitate the former reaction while Brønsted acid sites promote the
1
. Introduction
With the increase of general awareness of a low-carbon economy,
much attention has been placed on transformation of renewable
biomass-derived resources to the revised top chemicals such as 5-
hydroxymethylfurfural (HMF), furfural, 2,5-furandicarboxylic acid
2
1,22
later one.
1,2
3-5
(
FDCA), and N-containing furan derivative , so as to reduce Partially hydroxylated MgF , containing both Lewis and Brønsted
2
6
society’s dependence on petroleum-based chemicals. Among these acid sites, has been used as a heterogeneous catalyst for converting
compounds, HMF is identified as a primary intermediate for the xylose to furfural, in which 79% xylose conversion and 90% furfural
7
sustainable production of value-added chemicals and biofuels.
selectivity was obtained in water/toluene as solvent in 20 h at 160
23
Catalytic dehydration of fructose and glucose serves as a model ºC. MgF is also applied to dehydrate xylose and glucose, affording
2
8
reaction to synthesize HMF from biomass-derived carbohydrates.
HMF with 58% selectivity and 45.2% yield in a water/1-butanol
2
4
As compared with fructose, glucose is more abundant biphasic solvent at 160 ºC for 8 h. Most recently, AlF3−x(OH)x
monosaccharide found in nature, thus showing more beneficial for prepared by a sol-gel method was found to possess both Lewis and
9
a large scale production of HMF. In recent years, increasing Brønsted acid sites, as well as a high specific surface area (100-370
2
−1
attention has been paid to study on converting glucose to HMF.
m
g ), which was efficient for acylation of 2-methylfuran with
10
25
Various catalytic systems such as silica-supported boric acid,
acetic anhydride.
Motivated by above findings, partially
1
1
12
13
graphene oxide-ferric oxide, phosphate, niobia/carbon, InCl3- hydroxylated AlF was synthesized by a sol–gel route in the present
3
1
4
15,16
ionic liquids, functional polymeric ionic liquids,
mesoporous study, which was demonstrated to have high specific surface area
1
7
18
Al O -B O
3,
sulfated mesoporous niobium oxide and activated and Lewis-Brønsted dual acidic sites. The as-prepared catalyst was
2
3
2
1
9
carbon catalyst
have been developed for transforming further employed as a heterogeneous catalyst for conversion of
carbohydrates into HMF. Glucose can be dehydrated to HMF in the glucose as well as other biomass-derived saccharides to HMF, and
presence of homogeneous or heterogeneous acids. Among these effects of several key factors including reaction temperature,
catalytic systems, homogeneous acids generally have serious reaction time, and catalyst amount on HMF production were
deficiencies such as corrosion of equipment, hazard of handling, investigated.
production of waste, and poor recovery, while heterogeneous
2
. Experimental
catalysts are insoluble, easily separable from products, and
2
.1 Material
State Key Laboratory Breeding Base of Green Pesticide and Agricultural
Bioengineering, State-Local Joint Laboratory for Comprehensive Utilization of
Biomass, Center for Research and Development of Fine Chemicals, Guizhou
University, Guiyang 550025, China. Email: jhzx.msm@gmail.com, Tel:
Glucose was purchased from Sigma–Aldrich Corporation. Aluminum
isopropoxide (AlP) was bought from Zhejiang Maya reagent
Industrial. Dimethylsulfoxide (DMSO), and HMF were from Shanghai
Aladdin Industrial Inc. Other reagents used in this work were
purchased from Chongqing Chuandong Chemical Reagent Company.
+
86(851)8829-217, Fax: +86(851)8829-2170.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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All chemicals were of analytical grade and used without and a refractive index (RI) detector. During this process, the column
purification, unless otherwise noted. temperature remained constant at 65 ºC; while the mobile phase
used was 0.005 M H SO at a flow rate of 0.6 mL/min. The molar
2
4
2
.2 Catalysts preparation
concentrations of glucose and HMF were calculated according to
the standard curves. Glucose conversion rate (X, mol%) and HMF
yield (Y, mol%) were calculated as follows:
Partially hydroxylated AlF
3
samples were synthesized by a sol-gel
2
5
route, according to a reported method with slight modifications.
In a general procedure, aluminum isopropoxide (1.23 g, 6 mmol)
was introduced into 38 mL of anhydrous methanol (≥ 99.9%). After
stirring for 30 min, a stoichiometric amount of aqueous HF (0.90 g,
18 mmol, 40 wt% HF in water) was added into this suspension
under stirring condition. The resulting solution was stirred for 8 h
and aged overnight at ambient temperature. Then, the obtained sol
was dried in an oven at 100 ºC for 24 h to give a white powder,
3
. Results and discussion
followed by calcination under dry air at different temperatures of 3.1 Characterization of catalysts
50, 250 and 350 ºC for 5 h, and the obtained sample was denoted
AlF -T, where T corresponds to the calcination temperature.
3
-150 is shown in Fig. 1a. All peaks with 2θ ≈
1
The XRD pattern of AlF
5°, 30°, 40° and 45° are attributed to the cubic pyrochlore
3
1
For comparison, FeF
3
and MgF
2
were synthesized according to framework of AlF -150, which are in accordance with reported
3
2
5
26
reported procedures,
2 3
and commercially available Al O and results.
aluminum isopropoxide were also calcined under dry air at 150 ºC
for 5 h.
Structure property of AlF
in the range of 400−4500 cm , as illustrated in Fig. 1b. The sample
-150 was investigated by FT−IR spectrum
3
−1
−1
2.3 Catalysts characterization
exhibits peaks at around 1213 and 3442 cm , and a shoulder at
−
1
3
626 cm , which can be ascribed to the deformation δ(OH) and
stretching ν(OH) modes of isolated bridged Al–OH groups,
X-ray diffraction (XRD) measurements were carried out using a
D/Max-3c X-ray diffractometer with Cu Ka (λ = 0.154 nm), scanning
from 10° to 80° and using an operating voltage and current of 40 kV
and 30 mA, respectively. FT-IR spectra were recorded on an IR
26
–1
respectively, while the strong band at about 660 cm is assigned
27
to the Al–F stretch center of the corner-sharing Al–F octahedral.
prestige-21 FT-IR instrument (KBr disks). SEM was performed using The texture property of AlF -150 was evaluated by N adsorption–
3
2
a FESEM XL-30 (Philips) electron microscope. The microscopic desorption isotherm (Fig. 1c) and BJH pore-size distribution (Fig.
features were obtained by TEM on a JEM-2000FXII system operated 1d). From Fig. 1c, it can been seen that the hysteresis loop of
3
at 200 kV. NH -TPD was conducted on an AutoChem 2920 isotherm located in a wide range of relative pressure of 0.0–1.0
chemisorption analyzer. The Brunauer–Emmett–Teller (BET) strongly suggests the presence of microposes and mesopores in the
method was utilized to calculate the specific surface areas (SBET). samples, which is consistent with the pore-size distributions (Fig. 1d)
The pore volume (VBJH) and mean pore size (DBJH) were derived and TEM image (Fig S1). Table 1 summarizes BET surface areas and
from the adsorption branches of the isotherms using the Barrett– average diameters of AlF -150 and Al O . In comparison to Al O
3
2
3
2 3
2
-1
Joyner–Halanda (BJH) method. FT-IR of adsorbed pyridine was (pore diameter: 9.5 nm, and specific surface area: 185 m g ), AlF -
3
measured by Frontier FT-IR of PE Company.
150 possesses a relatively larger pore diameter of 17.5 nm but a
2
-1
lower specific surface area of 127.7 m g , which was deduced to be
2.4 Typical procedure for catalytic conversion of glucose into HMF
caused by assembly of AlF -150 particles to form intergranular
3
pores, as illustrated by SEM image (Fig. S2).
All glucose dehydration experiments were performed in a 15 mL
pressure tube under magnetic stirring condition, unless otherwise
3
mentioned. In a typical run, glucose (50 mg) and AlF -150 (20 mg)
were added into DMSO (1.0 g) in the reactor, which was then
immersed into the preheated oil bath. The reaction mixture was
stirred at a speed of 500 to 800 rpm for a specific reaction time.
Time zero was recorded when the reactor was immersed into the
oil bath. Upon completion, the mixture was decanted into a
volumetric flask using deionized water as diluent, and analyzed by
high performance liquid chromatography (HPLC).
2.5 Analytical methods
Glucose conversion and yield of HMF were analyzed by high-
performance liquid chromatography (HPLC; Agilent 1100, USA)
fitted with an Aminex HPX-87H column (Bio-Rad, Richmond, CA)
2
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Fig. 1 XRD pattern (a), FT-IR spectrum (b), N
2
adsorption–desorption isotherm (c), and 3.2 Synthesis of HMF from glucose catalyzed by various catalysts
3
BJH pore-size distribution (d) of AlF -150.
In this work, we initially studied the effect of various catalysts on
dehydration of glucose to HMF (Fig. 3). DMSO, a common and
cheap reagent, was used as solvent. AlF -150, Al , aluminium
isopropoxide (AlP), and AlCl were used to catalyze glucose
dehydration. Among above catalysts, AlF -150 was found to be the
Table 1 physicochemical properties of AlF
3
-150, reused AlF
3
-150, and Al
2
O
3
3
2 3
O
3
Acid distribution
BET
3
a
(
mmol/g)
surface
Pore
Total acid density best catalyst for transformation of glucose into HMF with 57.3%
Catalyst
2
-
b
area /m g
size/nm
(mmol/g)
2 3
yield and 95.5% glucose conversion at 140 ºC after 10 h. Al O
Brønsted
acid
Lewis
acid
1
afforded a HMF yield of 38.4% at glucose conversion of 90.9%
under identical reaction conditions. The presence of both Lewis and
Brønsted acid sites may contribute the higher catalytic activity of
AlF
3
-150
127.7
17.5
19.9
9.5
0.0305
0.0282
0
0.0669
0.0645
0.0698
3.25
2.64
2
1
AlF
catalysts AlP (pH = 5.65) and AlCl
glucose-to-HMF conversion, and a little difference in HMF yield (i.e.,
0.0% and 53.6%, respectively) and glucose conversion (i.e., 89.0%
3
-150 than that of Al
2
O
3
.
On the other hand, homogeneous
Reused
AlF -150
3
(pH = 4.47) were also used for
1
24
3
4
Al
2
O
3
185
2.14
and 93.0%, respectively) was observed, which indicates that the
homogeneous catalyst possessing more acidity is more
a
−1
Deduced from the intensity of the band of Brønsted acid located at 1540 cm and
−
1
3
2
Lewis acid at 1450 cm obtained from the adsorption-desorption of pyridine followed
advantageous to convert glucose to HMF. Other metal fluorides
i.e., FeF and MgF ) were also used for this reaction, while
by IR.
(
3
2
b
Total acid density quantified by NH
3
-TPD.
relatively lower catalytic performance (15.5% and 26.8%,
respectively) is observed, which could be ascribed to the lack of
2
3,25
Furthermore, NH -TPD was carried out to investigate acid strength Brønsted acid sites in these catalysts.
As a control experiment,
3
-150 catalyst (Fig. S3). The catalyst was found dehydration of glucose was also carried out without adding a
3
and density of the AlF
to possess two desorption bands: one big peak at a temperature of catalyst, and a low HMF yield of 11.5% and glucose conversion of
around 150 ºC and another small one at around 300 ºC, implying 30.5% were obtained. These results imply that AlF -150 having both
3
that the acidic centers of this sample was related to weak and Lewis and Brønsted acid sites can drive glucose dehydration to
medium strong acid sites, respectively. As shown in Table 1, AlF
3
-
HMF. AlF -150, therefore, was selected as the superior catalyst for
3
150 exhibited a higher acid density than the others, which was converting glucose to HMF in the following experiments.
possibly ascribed to the generation of more week acid sites after
introduction of Al species and hydroxyl groups.
The acid type on the surface of AlF
3 2 3
-150 and Al O were evaluated
by the pyridine adsorption IR spectra (Fig. 2). The bands at around
-
1
-1
1
453 cm and 1618 cm are assigned to Lewis acid sites associated
2
8,29
−1
with the non-coordinated Al sites,
while the peak at 1490cm is
possibly assigned to pyridine simultaneously adsorbed to Brønsted
3
0
and Lewis acid sites. As compared with Al
2 3
O , the spectrum of
-1
AlF -150 shows an additional band at 1540 cm , which is
3
characteristic of pyridine adsorbed on Brønsted acid sites derived
from OH, and its electronegativity can be enhanced by the
3
1
2 3
neighbour Al and F atoms. These results indicate that Al O
contains only Lewis acid sites, while the sol-gel synthesized AlF
has both Lewis and Brønsted acid sites.
3
-150
Fig. 3 Effects of various catalysts on dehydration of glucose to HMF (Reaction
conditions: 50 mg glucose, 1.0 g DMSO, 20 mg catalyst, 140 ºC, and 10 h).
3
.3 Effect of reaction time and temperature
In order to explore the effect of reaction conditions on glucose
dehydration, reaction temperature and time were firstly studied
and results are shown in Fig. 4. It can be seen that reaction
temperature immensely affects glucose-to-HMF conversion. When
dehydration of glucose was conducted at 120 ºC, the increase of
reaction time from 2 to 10 h resulted in an increase in HMF yield
and glucose conversion, while further increasing the reaction time
to 12 h led to a slight decrease of HMF yield and slight increase of
glucose conversion. On the other hand, if reaction temperature was
elevated to 140 ºC, same change trend to the reaction taking place
3 2 3
Fig. 2 Pyridine adsorption IR spectra of AlF -150 (a) and Al O (b)
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at 120 ºC was detected. Gratifyingly, HMF yield increased from amount of catalyst. Hence, 20 mg was chosen as the optimal dosage
1
6.4% (84.9% conversion) at 120 ºC to 57.3% (95.5% conversion) at of AlF
40 ºC after reacting for 10 h. Nevertheless, further increasing
3
-150.
1
reaction temperature to 160 ºC, along with the increase of reaction
time from 2 to 12 h, resulted in decreased HMF yields but increased
glucose conversions. These results indicated that dehydration of
glucose to HMF required a moderate temperature of 140 ºC, while
decreased HMF yields were observed at relatively higher
temperatures (e.g., 160 ºC), which might be caused by the unstable
2
3
structure of the catalyst.
Fig.5 Influence of AlF
3
-150 amount on production of HMF from glucose (Reaction
conditions: 50 mg glucose, 1.0 g DMSO, 140 °C, and 10 h).
3
.5 The effect of various solvents
3
3
34,35
The type of solvents such as ionic liquids and organic solvents
immensely affects the activity of glucose-to-HMF conversion. Fig. 6
illustrates the effect of various solvents on production of HMF from
3
glucose over 20 mg AlF -150 at 140 ºC for 10 h. In this study, HMF
yields of 17.5%, 4.1%, 57.3%, 4.6%, 8.5%, 23.7%, and 18.9% at
glucose conversion of 55.6%, 37.8%, 95.5%, 14.3%, 18.6%, 79.5%,
and 77.7% were found to be obtained from glucose in DMA, DMF,
DMSO, 1-butanol, 2-butanol, [BMIM]Cl and [BMIM]Cl/water,
respectively. It seemed that that side reactions were not dominant
during glucose dehydration in DMSO, and the formation of
byproducts such as levulinic acid and humins was inhibited by
36
DMSO.
Fig.4 Effect of reaction time and temperature on conversion of glucose to HMF
Reaction conditions: 50 mg glucose, 1.0 g DMSO, and 20 mg AlF -150).
(
3
3
3.4 Effect of AlF -150 amount
Fig. 5 shows the influence of AlF
3
-150 amount (i.e., 10 mg, 20 mg,
Fig.6 Effect of various solvents on production of HMF from glucose (Reaction
30 mg, 40 mg, and 50 mg) on dehydration of glucose to HMF.
conditions: 50 mg glucose, 1.0 g solvent, 20 mg AlF
water/[BMIM]Cl ratio
3
-150, 140 °C, and 10 h). 5/95 w/w
Increasing the catalyst amount from 10 to 20 mg resulted in an
increase in HMF yield from 38.6 to 57.3% and glucose conversion
from 86 to 95.5%. However, further increasing the catalyst amount
to 50 mg led to HMF yield decreasing from 57.3 to 13.5%, while
glucose conversion slightly changed from 95.5 to 96.5%. The
increase of catalytic activity should be attributed to an increase in
the availability of the number of active sites, while the decrease
may be caused by catalyst aggregation (e.g., electrostatic
3
.6 Synthesis of HMF from various carbohydrates catalyzed by
AlF -150
3
In order to explore the substrate scope of the catalytic system,
various carbohydrates including monosaccharides (fructose and
glucose), disaccharides (sucrose and cellobiose) and polysaccharide
interaction and bonding effect) that hinders the interaction (inulin) were employed as feedstock for HMF production, and the
between active sites and glucose molecules after adding an excess experimental results are presented in Fig. 7. Under the optimized
reaction conditions, the highest HMF yield 57.3% with conversion
4
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rate of 95.5% was obtained from glucose in DMSO. To our delight, AlF -150 was studied for dehydration of glucose to HMF under
3
high HMF yield of 54.3%, 55.0%, 40.6%, and 44.3% at conversion of
4.3%, 95.3%, 90%, and 93.1% could also be obtained, when inulin,
sucrose, cellobiose, and fructose were used as the substrate,
optimized reaction conditions (i.e., 50 mg glucose, 20 mg AlF
.0 g DMSO, 140 ºC, and 10 h). In a typical recovery procedure,
the catalyst was separated by centrifugation after reaction, which
was subsequently treated with 30% H at 100 °C in a Teflon-lined
3
-150,
9
24,37
1
respectively. The results illustrated that the AlF -150 catalyst
3
2 2
O
containing both Lewis and Brønsted acid sites was efficient for
transformation of carbohydrates that contain fructose and glucose
units into HMF.
flask under severe stirring for 4 h, followed by filtering, washing
with ethanol, and drying at 100 °C. The recovered catalyst was used
for the second cycle under the same conditions. The results in four
consecutive cycles are shown in Fig. S6, it was found that HMF
yields and glucose conversion slightly decreased from 57.3% to
4
5.6% and 95.5% to 89.3% in four consecutive cycles, respectively.
The IR spectrum (Fig.S7) and the wide-angle XRD profile (Fig.S8) of
the recovered AlF -150 are well consistent with those of the fresh
3
one. On the other hand, BET surface areas, BJH pore diameters, and
the results of pyridine adsorption IR spectra (Table 1) of the reused
3
and fresh AlF -150 samples are close to each other, revealing a
durable structure of the catalyst, which may be responsible for
relatively stable HMF yields of the recovered catalyst in recycles.
Fig.
3
7 Synthesis of HMF from different carbohydrates over AlF -150 (Reaction
conditions: 50 mg substrate, 20 mg catalyst, 1.0 g DMSO, 140 ºC, and 10 h)
3
.7 Influence of Brønsted acid site amount of AlF
3
The influence of Brønsted acid site contents of AlF
3
on dehydration
of glucose to HMF was studied. The results shown in Fig. 7
demonstrate that the yield of HMF decreases with the increase of
calcination temperature, which can be ascribed to a gradual
elimination of hydroxyl groups associated with Brønsted acidity at
2
3
high temperatures . In other words, higher Brønsted acid density
may afford increased HMF yields. In order to explore whether more
Brønsted acidity beneficial for a higher HMF yield, the content of
Brønsted acid was adjusted by addition of 15 μmol HCl (0.01 wt%)
Fig. 8 Influence of Brønsted acid site amount on dehydration of glucose to HMF
3 3
to the reaction system of AlF -250 and AlF -350 containing few
(
Reaction conditions: 50 mg glucose, 1.0 g DMSO, 20 mg catalyst, 140 ºC, and 10 h)
Brønsted acid sites (Table S1). It was found that increasing the
content of the Brønsted acid sites could increase the yield of HMF
and glucose conversion under identical reaction conditions. In order
to further study the synergy of Lewis and Brønsted acid sites in
a
0
.01 wt% HCl: 15 μmol.
4
. Conclusions
dehydration of glucose to HMF, we carried out a range of glucose Partially hydroxylated AlF -150 with Lewis and Brønsted acid sites
3
dehydration reactions over the catalyst AlF
and Brønsted acid sites at 140 ºC in different reaction periods (i.e., under atmospheric pressure and mild conditions. A high HMF yield
5 min, 30 min, 5 h, and 10 h). It can be clearly seen from Fig. S4 of 57.3% at glucose conversion of 95.5% could be achieved in the
3
-150 containing Lewis was capable of catalyzing conversion of glucose to HMF in DMSO
1
that fructose was formed from glucose via isomerization in the early presence of the AlF -150 catalyst at 140 ºC in 10 h. The presence of
3
stage (after reacting for 15 and 30 min). However, fructose was not both Lewis and Brønsted acid sites on AlF -150 was found to play a
3
stable enough after a little longer time (> 5 h), which will be further crucial role in this reaction.
dehydrated to HMF. These results illustrated that the activity of the
Acknowledgements
bifunctional catalyst is higher than the monofunctional acid (e.g.,
HCl) which is lack of active sites (i.e., Lewis acid sites) to promote
This work was financially supported by the Natural Science
glucose isomerisation, as shown in Fig. S5. It was indicated that
Foundation of China (No. 21576059), the Key Technologies R&D
Lewis acid would promote the isomerization of glucose to fructose,
Program (2014BAD23B01), the Research Project of Chinese Ministry
while Brønsted acid sites facilitated fructose dehydration to HMF,
of Education (213033A), the International Science & Technology
which is in consistent with the results reported by Behera and
21
Cooperation Program of China (2010DFB60840), and the Key S&T
Parida.
Projects of Guizhou Province (Nos. [2012]6012, [2011]3016 &
[
2008]70011).
3.8 Catalyst recycling
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Catalyst recycling is an important goal in liquid-phase reactions in
terms of green and sustainable chemistry. Thus, the recyclability of
1
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2
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RSC Advances
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DOI: 10.1039/C5RA24013A
Graphic Abstract:
Mesoporous AlF material bearing both Lewis and Brønsted acid sites exhibits high catalytic
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performance in glucose-to-fructose isomerization and subsequent dehydration to HMF (57.3% yield).