Selective yields of furfural and hydroxymethylfurfural from glucose in tetrahydrofuran over Hβ zeolite

Article abstract of DOI:10.1039/c8ra04060e

Several simple and effective solvents combined with Hβ zeolite were tested to selectively convert glucose into furfural and hydroxymethylfurfural in this work. The physicochemical properties of typically different polar aprotic solvents were compared. Tetrahydrofuran was found to be a suitable solvent in the selective conversion of glucose. The effect of reaction parameters, such as temperature, reaction time, water content, glucose dosage and protonic acid addition, on the product distribution were investigated in detail. Furfural and hydroxymethylfurfural could be selectively produced in this system, and the highest yields of furfural and hydroxymethylfurfural were up to 35.2% and 49.7% respectively. Furfural could be stable in a tetrahydrofuran medium when adding 5 wt% water in the absence of extra protonic acid. However, furfural production was extremely suppressed after addition of an acidic inorganic salt, which increased the yield of hydroxymethylfurfural. This investigation indicates a simple and feasible method to selectively produce furfural and hydroxymethylfurfural from renewable cellulosic carbohydrates.

Full text of DOI:10.1039/c8ra04060e

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Selective yields of furfural and
hydroxymethylfurfural from glucose in
Cite this: RSC Adv., 2018, 8, 24534
tetrahydrofuran over Hb zeolite†
abc
abc
Haiyong Wang,abc Longlong Ma,
Chenguang Wang,abc
*
Jin Tan,
Qiying Liu,
abc
abc
Qi Zhang
and Minghong Heabc
Several simple and effective solvents combined with Hb zeolite were tested to selectively convert glucose
into furfural and hydroxymethylfurfural in this work. The physicochemical properties of typically different
polar aprotic solvents were compared. Tetrahydrofuran was found to be a suitable solvent in the
selective conversion of glucose. The effect of reaction parameters, such as temperature, reaction time,
water content, glucose dosage and protonic acid addition, on the product distribution were investigated
in detail. Furfural and hydroxymethylfurfural could be selectively produced in this system, and the highest
yields of furfural and hydroxymethylfurfural were up to 35.2% and 49.7% respectively. Furfural could be
stable in a tetrahydrofuran medium when adding 5 wt% water in the absence of extra protonic acid.
However, furfural production was extremely suppressed after addition of an acidic inorganic salt, which
increased the yield of hydroxymethylfurfural. This investigation indicates a simple and feasible method to
selectively produce furfural and hydroxymethylfurfural from renewable cellulosic carbohydrates.
Received 13th May 2018
Accepted 25th June 2018
DOI: 10.1039/c8ra04060e
rsc.li/rsc-advances
and levulinic acid (LA) over acid catalyst.6–8 Production of FFA
from hexose is technologically challenging. However, some
Introduction
literatures have reported that lower yield of FFA can be formed
from hexose during hydrothermal treatment in the absence of
catalysts under extreme conditions (high temperature and high
pressure).9–12 Furthermore, FFA can be also achieved with high
selectivity in the catalytic fast pyrolysis of glucose by using ZK-5
zeolite via its small pore size.13 Until few years ago, Dumesic and
his team found that FFA as well as other products are easy to be
obtained from glucose under mild conditions over Hb zeolite in
g-valerolactone (GVL)/water solvent and they present a view-
point that the use of zeolite catalysts in lactone/water solvents
offers new routes for the selective conversion of renewable
biomass feedstocks.14 Then Hb zeolite combined with g-butyr-
olactone (GBL)/water are adopted to convert hexoses and other
cellulosic carbohydrates (e.g., glucose, fructose, sucrose, cellu-
lose) into FFA.15 In order to achieve FFA with higher yield from
hexoses or cellulosic carbohydrates, the modied versions of
Hb zeolite (Fe, Zn and Zr metals are loaded on the Hb zeolite via
ion-exchanged route respectively) are tested to be efficient
catalysts for FFA production in GVL.16
Furfural (FFA) and hydroxymethylfurfural (HMF) are two
versatile kinds of furanic compounds, which are used for the
production of a wide range of non-petroleum derived chem-
icals.1 However, there is no synthetic route available for FFA and
HMF production in the chemical industry yet.2 Commonly, FFA
is commercially produced from bagasse, corncob and oat hulls
with sulfuric acid treatment, in which hemicellulose fractions
are hydrolyzed to pentoses, followed by the dehydration of
pentoses (xylose) to FFA by mineral acid.3 This industrial
process for FFA production not only consumes large amounts of
steam, but also generates a great deal of acidic residues which
mainly consist of cellulose and lignin.4,5 That is, the valuable
fractions of raw material for FFA production from renewable
biomass only depend upon hemicellulose, and a large amount
of cellulose is abandoned as waste. Utilization of the abundant
cellulose fractions in hydrolysis residues will enrich the feed-
stock source in producing FFA and HMF.
It is generally assumed that cellulose is composed of glucose
and this hexose undergoes successive dehydration to form HMF
According to the possible mechanism of glucose to FFA,
isomerization of glucose into fructose is an important step over
Lewis acid site and the produced fructose is the substrate for the
rearrangements and the retro-aldol condensations.15,17 Nowa-
days, the catalysts used in the isomerization are divided into
enzyme, Lewis acid and base catalyst. The best catalyst for
isomerization is enzyme. However, this process suffers from
various drawbacks such as the need of low concentrated
aGuangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS),
510640, Guangzhou, China. E-mail: mall@ms.giec.ac.cn
bCAS Key Laboratory of Renewable Energy, 510640, Guangzhou, China
cGuangdong Provincial Key Laboratory of New and Renewable Energy Research and
Development, 510640, Guangzhou, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra04060e
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solutions of glucose with high purity and limited operating 0.5 g of glucose, 0.1 g of Hb zeolite and 9.5 g of solvent were put
temperature range.18 As for base catalyst, monosaccharides are into the reactor. In order to avoid oxidation, high purity
unstable under strong alkaline conditions and degrade into nitrogen was used to remove air inside the reactor. Aer that,
more than 50 different byproducts.19 Therefore, most work have the reactor was heated to the expectant temperature and
been conducted on Lewis acid catalysts. Among the various maintained for a certain period of time. The reaction was halted
Lewis acid catalysts, Hb zeolite before and aer dealuminizing and the system was cooled down to room temperature by cold
procedure are tested to be an efficient catalyst for isomeriza- water when reaction was completed. The mixed liquid and
tion.20 Meanwhile, Hb zeolite is compatible with the subsequent catalyst was separated through a centrifuge at the rotational
dehydration reaction for FFA and HMF production from glucose speed of 5000 rpm for 5.0 min. The programs for catalyst recycle
due to the physicochemical properties, which the enriched were performed aer Hb zeolite was calcined again at 823 K for
Lewis acid sites on the external surface are in favor of isomer- 300 min.
ization, and the strong Brønsted acid sites located in micro-
pores are the active sites for hydrolysis reaction to FFA, HMF
Analytic methods
and LA formation.21
The qualitative analysis of glucose, fructose, FFA, HMF and LA
All of those investigations verify a fact that not only hemi-
cellulose but also cellulose can be converted to FFA. However, it
were determined using HPLC (Waters 2695) equipped with
a SH1011 column (8.0 ꢀ 300 mm, 6 mm particle size, Waters)
is obviously noticed that the mediums playing for FFA and HMF
through an external standard method. The mobile phase was an
production from hexoses or cellulosic carbohydrates only
aqueous solution of sulfuric acid (5 mM) at the ow rate of 0.5
depend upon the lactone/water.14–16,22–24 Despite the excellent
mL minꢁ1 and the column was kept at 323 K. A Waters 410
properties of lactone (e.g., GVL, GBL) in biomass conversion, the
refractive index detector (operated at 318 K) was adopted to
large-scale and industrial synthesis of lactone is highly limited
detect glucose, fructose and LA, while a UV detector (with the
due to the reduction of commercially synthetic materials.25
wavelength of 284 nm) was used to detect HMF and FFA. All
Tetrahydrofuran (THF), a sustainable kind of polar aprotic
liquid samples obtained aer each experiments were diluted 20
times by deionized water before analysis. The relevant calcula-
solvent as well as lactone, is derived from renewable biomass
directly.26 Moreover, it has a similar ve-membered ring struc-
tions for glucose conversion, mole yields of different products
ture with that of lactone. It is deduced that the synergistic effect
and carbon balance were in the following formulas:
between Hb zeolite and lactone enables the selective C–C bond
cleavage of hexoses into pentoses and promotes the subsequent
dehydration of pentoses to FFA.14,15 In this work, THF medium
combined with Hb zeolite was performed to break through the
limitation for solvent (lactone) application in the selective
synthesis of FFA and HMF from hexoses or cellulosic carbohy-
drates. Thus, a cost-effective reaction system (Hb zeolite and
THF) was employed and the inuential mechanism on products
distribution were investigated in detail. The reaction conditions
of this system for the selective conversion of glucose to FFA and
HMF were discussed.
n0 ꢁ nl
conversion ð%Þ ¼
ꢀ 100%
(1)
(2)
n0
ni
mole yield ð%Þ ¼
ꢀ 100%
n0
P
nc
i
carbon balance ð%Þ ¼
ꢀ 100%
(3)
6n0
In the formula (1), n0 and nl are the mole content of glucose
before and aer reaction. In the formula (2), n0 represents the
same meaning as in the formula (1), ni was the mole content of
each product (fructose, FFA, HMF, LA and formic acid) respec-
Experimental
Materials
tively. In the formula (3), nc is the total carbon mole content of
i
Hb zeolite (Si : Al ¼ 25) was provided by catalyst plant of Naikai
University, China. Fructose (purity > 99.0%) was purchased
from MYM Biological Technology Company Limited; glucose
and KHSO4 were all obtained from Damao Chemical Reagents
Company, China. Tetrahydrofuran (THF), dimethyl sulfoxide
(DMSO), sulfolane, dioxane and N,N-dimethylformamide (DMF)
were bought from Guangdong Guanghua Sci-Tech., Co., Ltd.,
China. The standard compounds of FFA, HMF and LA were all
purchased from Aladdin Reagent Company. All reagents were of
analytical grade and used without further purication.
each product (fructose, FFA, HMF, LA, formic acid and black
char).
Results and discussion
Production of FFA from glucose in various solvents
In order to compare the properties of different solvents in the
conversion of glucose into FFA, HMF and LA, several typically
common solvents (e.g., THF, sulfolane, DMSO, dioxane and
DMF) which have the same polar aprotic properties as lactone
are selected as the reaction mediums.26–28 Table 1 shows the
differences of ve commonly used dipolar aprotic solvents in
Reaction procedure
Hb zeolite was put into a furnace and calcined at 823 K for physicochemical properties. Lower boiling point (339 K) of THF
300 min. Then conversion of glucose into FFA and HMF was indicates that it can be recycled easily when used as reaction
conducted in a 25 mL stainless steel reactor with a Teon inner. solvent.26
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Table 1 Physicochemical properties of five commonly used dipolar
less polar phase is used to protect them (sugars, FFA, HMF and
LA) from further exposure to the acidic catalyst in the polar
phase.33
aprotic solvents29,30
Solvents
Hb zeolite in an aprotic organic solvent affects the reaction
kinetics by changing the stabilization of the acidic proton
relative to the protonated transition state.28 According to the
physicochemical properties in Table 1, it is easy to note that
THF and dioxane have smaller dipole moments, which show
weaker polarity of THF and dioxane compared with that of the
other solvents. The reactivity of Hb zeolite in the solvent is
similar to that of a strong homogeneous Brønsted acid, which
depends upon the extent of proton solvation relative to the
polarity of solvent.28
Property
Sulfolane DMSO DMF THF Dioxane
Molecular weight
120.2
1.3
78.1
1.1
73.1
0.9
72.1 88.1
0.9 1.0
Density (g cmꢁ3
)
Boiling point (K)
Freezing point (K)
Permittivity (3y) @298 K
Dipole moment (Debye)
Viscosity (MPa s) @303 K 10.4
560.3
301.4
43.4a
4.7
462.1 426.1 339.0 374.0
291.6 212.6 165.0 284.8
46.7
4.0
36.7
3.9
7.6
1.7
0.6
2.2
0.5
1.1
2.0b
0.9c
Flash point (K)
Autoignition point (K)
450.0
801.0
362.0 331.0 290.2 288.6
575.0 718.0 594.1 353.0
Consequently, the generated furans (HMF and FFA) are
prone to degradation/polymerization in the strong polar
solvents.34,35 For example, they are ineluctable to repolymeriza-
tion with hexoses and other chemicals to humins through aldol
reaction and self-condensation over acid catalysts.36 In addition,
these solvents give different products distribution, possibly due
to the different synergistic effects between Hb zeolite and
aprotic organic solvents.24
a
b
Mean the temperatures at 303 K. Mean the temperatures at 298 K.
Mean the temperatures at 293 K.
c
Usually, the use of organic solvents in biomass conversion
reactions can lead to high rates and improve selectivities
through affecting the solubilities of substrate fractions and
affecting chemical reaction thermodynamics.27,31 However, the
yield and selectivity of FFA from hexoses and various cellulosic
carbohydrates are signicantly affected by the synergistic effects
of zeolite and solvent.15 In this investigation, it is clearly seen
from Fig. 1 that the highest total yield of FFA, HMF and LA was
achieved at 49.4% in THF, followed by dioxane (43.8%).
Although glucose has a high conversion in those solvents, the
yields of FFA in sulfolane and DMSO are low, especially in DMF
(because of the heavy char formation).
The selectivities of FFA, HMF and LA in various solutions
show that FFA has the highest selectivity in THF, sulfolane and
dioxane, and DMSO medium is in favor of HMF production
(Fig. S1†). Different products selectivities are detected in various
mediums by altering the extents of solvation of the initial and
transition states of these catalytic processes.31 Moreover, solvent
with different properties have different ability to transfer the
hydrogen ions, which changes dispersion of hydrogen ions in
solvent and further affect their catalytic behaviors.32 Generally,
the polar phase is used to dissolve and convert sugars while the
Effect of the temperature on products distribution
Fig. 2 shows the versatile products distribution with increasing
reaction temperature from 413 K to 493 K. Fructose, FFA, HMF
and LA were identied as the main products when glucose was
used as substrate (Fig. S2†). As the reaction proceeded,
a signicant effect of reaction temperature on the yield of
different products has been observed. Obviously, only 5.3%
yield of fructose was detected as the main product at 413 K
accompanied by a few FFA and HMF. However, the highest total
yield of FFA, HMF and LA was obtained at 56.2% with an
increase in the reaction temperature at 453 K. Meanwhile, there
was nearly no fructose appeared in this mixture (the yield of
fructose was only about 0.5%). According to the possibly
proposed pathway of FFA and HMF production from glucose,
fructose is a key intermediate product through isomerization
over Lewis acid, which is ready for the next rearrangements and
retro-aldol condensations to FFA production.11,17 The enriched
Fig. 1 Yields of FFA and other products in different solvents over Hb Fig. 2 Effect of the different temperature on products distribution.
zeolite. Reaction conditions: 0.5 g glucose, 0.1 g Hb zeolite, 9.5 g Reaction conditions: 0.5 g of glucose, 0.1 g of Hb zeolite, 9.0 g of THF,
solvent, 453 K, 120 min.
0.5 g of water, 120 min.
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Lewis acid sites on the external surface of Hb zeolite are in favor rehydration of HMF to LA and formic acid could be enhanced.41
of isomerization, while the strong Brønsted acid sites located in Meanwhile, the undesired side reactions, such as polymeriza-
micropores are the active sites for hydrolysis reaction to HMF tion between sugars, FFA, HMF, and LA, are also accelerated
and LA formation.21 Herein, both bifunctional acid active sites due to the enhanced polarity of solution. Based on these
resulted in the FFA, HMF and LA coproduction under this reasons, the yields of FFA, HMF and LA were achieved at 5.0%,
circumstances. Although higher temperature could accelerate 22.1% and 5.3% in the absolute water respectively. The sharply
the rate of chemical reaction, the unwanted side reactions also changed conversion of glucose was attributed to the undesired
appeared at the same time. Moreover, these side reactions are coke formation in water medium.42
much more thermally sensitive than other benecial reactions
for FFA, HMF and LA production,37 which results in the sharp
Effect of the prolonged time on products distribution
decline of total yields at higher temperature.
A typical time prole for the products distribution was per-
formed and the results are exhibited clearly in Fig. 4. The
changed yield curves of fructose, FFA, HMF and LA suggests
a close relationship between relevant intermediate chemicals
when glucose is converted in THF/water solution over Hb
zeolite. Obviously, fructose was the main product in a short
period of time (9 min), and it reduced gradually as time was
prolonged to 360 min. Usually, LA comes from the rehydration
of HMF following fructose dehydration over acid catalysts.43–45
Consequently, a decrease of fructose results in the increase of
HMF and LA at a certain period of time. The highest yield of
HMF was obtained at 31.9% when reaction time was prolonged
to 360 min.
Effect of the water content on products distribution
Water is not only a solvent in this system, but also a product of
the dehydration procedure, involved in each step from glucose
to FFA, HMF and LA.35 Previous investigation demonstrates that
FFA and HMF yields and selectivity are signicantly affected by
solvent and cosolvent.38 In this work, the inuence of the water
percentage on products distribution was investigated and the
results are showed in Fig. 3. Commonly, addition of organic
solvent allows to suppress the activity of external acid sites of
Hb zeolite in the side reactions with increase in the selectivity to
HMF and LA at high glucose conversion.39
It is interesting to note that the yield of FFA reached the
maximum value only at the time of 120 min as well as a high
conversion of glucose. Stable yield of FFA was at about 24.4% no
matter reaction time was further prolonged to 420 min. This
result indicates a fact that the degradation of FFA is suppressed
drastically by THF. All of these results show a parallel reaction
routes for glucose conversion:11,17 (i) isomerization of glucose
into fructose and successive dehydration to HMF and LA. (ii)
Conversion of the isomerized fructose into FFA through rear-
rangements and retro-aldol condensations.
Since glucose does not dissolve in the absolute organic
solution, it is rst converted to organic-soluble oligomers which
could be reverted to glucose if diluted in water at mild condi-
tions.40 Therefore, newly isomerized fructose were converted to
FFA, HMF and LA rapidly with parallel reactions in the pure
THF medium. Consequently, the nal products mainly con-
sisted of FFA, HMF and LA, and the total yield was achieved at
49.4%. More and more fructose were detected with the increase
of water percentage from 0 wt% to 40 wt%. On the contrary, the
total yield of FFA, HMF and LA declined to 24.9%.
Previous investigation reveals that the interaction between
solvents and acidic catalysts is affected obviously by the polar-
Effect of the glucose dosage on products distribution
ities of solution, determining availability of the acidic sites on According to previous literatures, glucose isomerization, fruc-
the surfaces of the catalysts.35 Furthermore, the degradation of tose diffusion and retro-aldol condensations are the three
FFA is found to be suppressed drastically by the shielding effect essential steps for FFA and HMF production.11,15,17 Initial
of solvent.34 With increasing the content of water in THF, the substrates with high concentration can accelerate their diffused
Fig. 3 Effect of the different water content on products distribution. Fig. 4 Effect of the different reaction time on products distribution.
Reaction conditions: 0.5 g of glucose, 0.1 g of Hb zeolite, 9.5 g of Reaction conditions: 0.5 g of glucose, 0.1 g of Hb zeolite, 9.5 g of THF,
solvent, 453 K, 120 min.
0.5 g of water, 453 K.
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Table 2 Effect of the glucose dosage on products distributiona
Yields/%
Glucose
dosage/wt%
Black char
(C mol)
Entry
Conversion/%
FFA
HMF
LA
Formic acid
Glucose
Fructose
Carbon balance/%
1
2
3
4
5
6
7
8
9
10
0.1
0.3
0.5
1.0
2.0
3.0
4.0
5.0
6.0
8.0
100
100
100
100
100
99.5
99.5
99.2
97.3
96.6
31.9
33.3
33.9
34.3
35.2
32.6
31.1
25.9
20.7
15.4
15.4
15.4
19.4
19.5
27.5
30.4
28.0
23.3
22.3
20.4
—
—
—
—
—
—
—
—
—
—
—
—
—
0.5
1.4
2.5
1.2
6.7
8.5
12.9
18.9
19.6
22.4
23.6
25.1
30.6
43.9
56.8
63.8
66.4
80.5
81.7
80.5
71.1
70.2
71.1
3.8
4.5
5.4
4.8
4.0
3.5
1.7
1.4
1.4
4.2
4.3
4.8
5.3
3.7
3.9
2.4
1.9
1.8
—
0.5
0.5
0.8
2.7
3.4
a
Reaction conditions: m(glucose + THF) ¼ 9.5 g, 0.1 g of Hb zeolite, 0.5 g of water, 453 K, 120 min.
rate into zeolite pores, which increases the risk for byproducts decrease aer four recycling runs. For example, the total yield of
formation.46 Therefore, the yields of FFA, HMF and versus the FFA, HMF and LA was 67.5% over fresh Hb zeolite, while it
glucose dosage were investigated and the results are exhibited decreased to 47.7% aer Hb zeolite was calcined 4 times. With
in Table 2. Obviously, higher yields (>30%) of FFA were obtained increasing the recycle times, the specic surface area and the
when glucose dosage was lower than 4.0%. However, it acid centers of Hb zeolite were decreased in the THF/water
decreased to 15.4% sharply when 8.0 wt% glucose was used. medium under those conditions.21
The yield of HMF showed the same changes as FFA and the
highest yield was achieved at 30.4% when glucose dosage was
3.0 wt%. These declines are attribute to the covered carbon
Usually, the ability to form Brønsted acid sites for Hb zeolite
deposition on the Lewis and Brønsted acid sites of Hb zeolite.15
The characterization of Hb zeolite before and aer reaction
supported this viewpoint. The results of XRD patterns of Hb
zeolite before and aer reaction show that catalyst almost
remained integrity crystal structure (Fig. S3†). While carbon
deposition was found on the surface external and internal
surface (Fig. S4†), which resulted in the decrease of BET surface
area and pore size (Table S1†). Moreover, these undesired
acid on FFA and HMF production and the results are listed in
carbon deposition covered the Lewis and Brønsted acid sites on
the surface of Hb zeolite, and decreased the effective active sites
for FFA and HMF production (Fig. S5 and Table S2†) (Fig. 5).
Hence, the Hb zeolite aer one recycling run was calcined at
823 K for 300 min and used for the next run (Fig. 4). The activity
Selective production of HMF from glucose
and other catalysts are relative to the polarity of solvent, which
is a key factor for FFA and HMF production.28 It is well known
that lone electron pairs and no acidic hydrogen centers are two
obvious features of polar aprotic solvent.27 Therefore, stable
yield of FFA was detected in the mixture of various compounds
under an extent of protonic acid. Additional H+ (KHSO4) was
introduced into this reaction system to test the effect of protonic
Table 3. An increase of H+ was in favor of HMF and LA
production, which sharply restrained the yield of FFA. 35.2%
yield of FFA was obtained without adding H+, but the yield of
FFA was only 5.9% aer the extra H+ (0.2 mmol) addition. On
the contrary, the yield of HMF increased from 27.5% to 49.7% as
of Hb zeolite for FFA, HMF and LA production show a slight
extra H+ dosage increased from 0 mmol to 1.2 mmol gradually.
Commonly, KHSO4 presents as solid in THF solvent with no
water addition due to its poor solubility. The aqueous solution
in this reaction system can be saturated by adding enough
KHSO4, resulting in the separation of THF and water by salting-
out effect and the formation of microemulsion system auto-
matically.8 This newly produced microemulsion system is in
favour of glucose dehydration in aqueous phase over protonic
acid and HMF shi into THF, which results in the HMF increase
(Fig. 6).6–8
According to the previous literature and the results of this
work, the conguration transformation of monosaccharides,
including ring opening, isomerization, ring closing, are the
signicant intermediate steps for FFA, HMF and LA production
from glucose.11,15,17 The changed content of fructose in a short
period of time indicated that it is a transitional product during
glucose conversion in THF/water solution over Hb zeolite.
Fig. 5 Recycle of Hb zeolite. Reaction conditions: 0.2 g of glucose,
0.1 g of Hb zeolite, 9.5 g of THF, 0.5 g of water, 453 K, 120 min.
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Table 3 Products distribution after adding different content of H+a
Yields/%
H+ dosage/
mmol
Black char
(C mol)
Entry
Conversion/%
FFA
HMF
LA
Formic acid
Glucose
Carbon balance/%
1
2
3
4
5
6
0
100
35.2
5.9
5.8
5.8
5.8
5.1
27.5
29.2
35.3
41.7
45.2
49.7
4.8
2.7
3.5
3.9
5.0
5.6
5.3
1.2
4.0
4.8
6.5
6.1
—
18.9
23.6
24.3
24.9
25.2
25.9
80.5
77.6
77.8
83.4
83.4
86.6
0.2
0.3
0.6
0.9
1.2
82.5
90.1
92.0
97.0
98.8
17.5
9.9
8.0
3.0
1.2
a
Reaction conditions: 0.2 g of glucose, 0.1 g of Hb zeolite, 9.5 g of THF, 0.5 g of water, 453 K, 120 min.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 51536009), Local Innovative and
Research Teams Project of Guangdong Pearl River Talents
Program (No. 2017BT01N092) and the Natural Science Foun-
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