Effect of Br?nsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural over Mesoporous Nb and Nb-W Oxides

Article abstract of DOI:10.1002/cjoc.201700084

A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the conversion of glucose to 5-hydroxymethylfurfural (HMF). The results of solid state ³¹P MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Br?nsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides varied with the ratio of Br?nsted to Lewis acid sites and high glucose conversion was observed over Nb₅W₅ and Nb₇W₃ oxides with high ratios of Br?nsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity of HMF, whereas no HMF forms over sulfuric acid due to its pure Br?nsted acidity. The results indicate fast isomerization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Br?nsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H₂O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over Nb₇W₃ oxide. The 2-butanol/H₂O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb₅W₅ oxide.

Full text of DOI:10.1002/cjoc.201700084

FULL PAPER
DOI: 10.1002/cjoc.201700084
Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars
to 5-Hydroxymethylfurfural over Mesoporous Nb
and Nb-W Oxides
Bin Guo,a Lin Ye,a Gangfeng Tang,a Li Zhang,a Bin Yue,*,a Shik Chi Edman Tsang,b
and Heyong He*,a
a Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Col-
laborative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai 200433, China
b Wolfson Catalysis Centre, Department of Chemistry, University of Oxford, Oxford OX1 3QR, UK
A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con-
version of glucose to 5-hydroxymethylfurfural (HMF). The results of solid state 31P MAS NMR spectroscopy with
adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number
of Brønsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides
varied with the ratio of Brønsted to Lewis acid sites and high glucose conversion was observed over Nb5W5 and
Nb7W3 oxides with high ratios of Brønsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity
of HMF, whereas no HMF forms over sulfuric acid due to its pure Brønsted acidity. The results indicate fast isom-
erization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Brønsted
acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H2O system enhances the
HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over
Nb7W3 oxide. The 2-butanol/H2O catalytic system can also be employed in conversion of sucrose, achieving HMF
selectivity of 46% over Nb5W5 oxide.
Keywords carbohydrates, glucose, HMF, Nb-W oxide, heterogeneous catalysis
Introduction
of glucose in comparison with fructose make it more
reasonable to be a better feedstock. Unfortunately, the
direct dehydration of glucose leads to low selectivity of
HMF due to side reactions like unselective condensation
of glucose to by-products such as humins.[24] The yield
of HMF can be increased significantly by initial isom-
erization of glucose to fructose over Lewis acid sites in
tandem with dehydration of fructose over Brønsted acid
sites.[25] Hence, the challenge to transform glucose to
HMF is to develop catalysts and reaction systems which
can achieve balanced functions of the isomerization of
glucose to fructose and the dehydration of fructose to
HMF.
Zhao et al. reported the highest HMF yield of near
70% in ionic liquids with CrCl2 catalyst.[26] Since then,
many studies have been explored in similar catalytic
system of different metallic salts in acidic medium, such
as AlCl3 combined with Brønsted acid HCl,[17,24] wa-
ter-compatible lanthanide-based Lewis acids in biphasic
systems,[27] and Zr(O)Cl2/CrCl3 catalyst in N,N-dimeth-
yl acetamide solvent containing LiCl under microwave
assisted heating.[28] Other studies were also carried out
Biomass as a renewable feedstock has been inten-
sively studied for the production of fuel and fine chem-
icals.[1-8] Carbohydrates, the most important fractions of
biomass and the largest natural source of carbon, show
great potential for the production of useful platform
chemicals such as 5-hydroxymethylfufural (HMF).[9-13]
As a platform chemical, HMF can be converted to use-
ful products, such as 2,5-furandicarboxylic acid to re-
place terephthalic acid in the polyethylene terephthalate
industry and adipic acid used in the nylon industry.[14-15]
The C6 sugars, glucose and fructose, have been em-
ployed as feedstocks for the formation of HMF. Fruc-
tose dehydration to HMF can be realized over Brønsted
acid sites more easily than glucose because the reactivi-
ty of fructose (ketose) is higher than that of glucose
(aldose) in aqueous solution. Great success has been
achieved on fructose dehydration to HMF over homo-
geneous and heterogeneous acidic catalysts in
aqueous[16] or multiphase systems[12,17,18] and ionic liq-
uids.[19-23] However, the low price and high availability
*
E-mail: heyonghe@fudan.edu.cn; Tel.: 0086-021-65643916, Fax: 0086-021-65643916
Received January 30, 2017; accepted April 27, 2017; published online XXXX, 2017.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201700084 or from the author.
Chin. J. Chem. 2017, XX, 1—11
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Guo et al.
FULL PAPER
[30]
[31]
in aqueous system with ZnCl2,[29] CrCl3 and WCl3
desired amount of WCl6 (99＋%, Strem Chemicals) and
NbCl5 (total of 12 mmol of metal chloride) with vigor-
ous stirring at room temperature for 30 min, then 1.08 g
of de-ionized water was added with further stirring for
ca. 2 h. The resulting sol was gelled on a glass plate at
40 ℃ under controllable humidity of ca. 45% for 5 d.
The aged gel samples were calcined at 460 ℃ for 5 h
in air to remove the block copolymer surfactant.
Nb2O5•nH2O was prepared following a procedure
reported by Nakajima et al.[32] A mixture of NbCl5 (5 g)
and de-ionized water (200 mL) was stirred at room
temperature for 3 h. The white precipitate was filtered
and then washed several times with de-ionized water
until neutral. The sample was finally dried overnight at
353 K.
catalysts. However, the main disadvantages of all these
catalytic systems are high costs of ionic liquids, corro-
sion in the use of minerals acids, or difficult recovery of
catalysts from the reaction medium. For industrial ap-
plications, heterogeneous catalysts are more preferred in
the reaction of glucose to HMF.
Niobic acid (Nb2O5•nH2O)[32] and hydrated tantalum
oxide (Ta2O5•nH2O)[33] which have both Brønsted and
Lewis acidities display remarkable activity in the dehy-
dration of glucose to HMF. Moreover, mesoporous ma-
terials like tantalum oxide,[34,35] zeolite Sn-beta[36] and
TiO2[37] have also been employed as catalysts. In a sim-
ilar way, surface modified metal oxides such as
SO42/ZrO2 and SO42/ZrO2-Al2O3,[38] metal(IV) phos-
phates[39-40] and phosphate/TiO2[41] can somehow inhibit
side reactions and improve HMF selectivity. However,
the possible leaching of sulfate or phosphate species
may cause a poor catalyst reusability, as reported for
sulfated zirconia, tantalum phosphate and niobium
phosphate.[35,42-43] Recently, Guo et al.[44] studied the
catalytic activity of Nb-W oxides on glucose dehydra-
tion to HMF in aqueous system at 120 ℃. However,
systematic investigations, especially the addition of or-
ganic phase to achieve high catalytic performance, are
still worth being carried out for better understanding the
relationship between the Brønsted/Lewis acidity and
catalytic activity.
Catalyst characterization
The textural properties of the catalysts were evalu-
ated from nitrogen adsorption-desorption isotherms at
77 K, using a Quantachrome Quadrasorb SI apparatus.
The samples were degassed at 523 K for 3 h before each
experiment. The surface areas were calculated using the
BET method. Pore size distribution curves were derived
from the desorption branches of isotherms and calcu-
lated by the BJH model. Transmission electron micros-
copy (TEM) images were obtained with a JEOL
JEM2010 transmission electron microscope. Solid-state
nuclear magnetic resonance (NMR) spectra were ob-
tained on a Bruker Avance III 400 spectrometer.
In this work, we studied the role of the type and
amount of Lewis and Brønsted acid sites on different
mesoporous niobium oxides and Nb-W oxides with spe-
cific ratios of Nb to W in the transformation of glucose
to HMF. Moreover, the influences of different experi-
mental parameters, such as adding organic phase, reac-
tion temperature and time, dosage of catalyst, along
with reusability, have been evaluated to achieve high
catalytic performance.
High-power H decoupling 31P magic angle spinning
1
(MAS) NMR spectra were acquired at 161.9 MHz using
a 30° pulse and a recycle delay of 15 s at a spinning rate
of 12 kHz with 4 mm zirconia rotor. NH4H2PO4 was
used as a standard sample for chemical shift referencing
(δ 0.81) and the external intensity standard to quantify
the signal. Trimethylphosphine (TMP) was employed as
a probe molecule for the acidity study. About 200 mg of
powdered sample was placed in a home-made glass tube
and activated at 300 ℃ for 90 min under vacuum (101
Pa) to ensure maximum adsorption of TMP molecules
by using a vacuum system. Then, the sample tube was
flame sealed for storage and transferred in a glovebox
under nitrogen atmosphere in order to repack the
TMP-adsorbed samples into a Bruker 4 mm ZrO2 rotor.
Experimental
Catalyst preparation
Mesoporous niobium oxide with amorphous walls
was prepared following the procedures previously re-
ported by our laboratory under controlled relative hu-
midity using triblock copolymer P123 (EO20PO70EO20,
Sigma Aldrich), niobium pentachloride (NbCl5, 99＋%,
Strem Chemicals) and n-propanol.[45] The solution con-
taining 2.56 g of P123, 20 g of n-propanol, and 3.78 g
(14 mmol) of NbCl5 was stirred vigorously at room
temperature for 30 min, then 2 g of de-ionized water
was added with further stirring for ca. 2 h. The resulting
sol was gelled on a glass plate at 40 ℃ under control-
lable humidity of ca. 45% for 5 d. The aged gel sample
was calcined at 450 ℃ for 5 h in air to remove the
block copolymer surfactant.
Catalytic activity measurement
The catalytic reaction was carried out in a 50 mL
autoclave and heated in a temperature controlled oil
bath with magnetic stirring. The reaction was performed
by using 0.1 g of catalyst and 5 mL of 2 wt% of sub-
strate. For the 2-butanol/H2O catalytic reaction system,
2-butanol was introduced to aid in removing the formed
HMF from catalyst surface. In this way, the further
degradation of HMF can be suppressed.[12] Typically, a
2-butanol/H2O (5∶2, V/V) system was performed by
using 0.05－0.3 g of catalyst and 2 mL of 1 wt%－10
wt% of substrate and 5 mL of 2-butanol. The reactor
was raised to certain temperature and held for a given
Mesoporous Nb-W oxides with different Nb/W mo-
lar ratio, Nb5W5, Nb7W3 and Nb9W1, were synthesized
by dissolving 2.56 g of P123, 20 g of n-propanol, and
2
www.cjc.wiley-vch.de
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2017, XX, 1—11

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural
reaction time. After reaction, the reactor was quenched
immediately with cold water. In both aqueous and
2-butanol/H2O systems the mixture was centrifuged and
the liquid samples were filtered through a 0.25 µm filter
before analysis. Liquid samples were analyzed by
HPLC equipped with refractive index and UV-Vis de-
tectors at wavelength of 284 nm with a Biorad©
Aminex HPX-87H sugar column. The mobile phase was
0.005 mol/L H2SO4 aqueous solution flowing at a rate
of 0.6 mL/min at 35 ℃.
panied with the decrease of pore volume from 0.32
cm3•g1 to 0.21 cm3•g1 and the pore diameter from 7.4
(mesoporous niobium oxide) to 6.0 nm (mesoporous
Nb5W5 oxide). TEM images of these Nb-W oxides are
shown in Figure 2. It can be seen that all the oxides
have wormlike mesopores, and a slight decrease of uni-
formity was observed for Nb5W5 oxide with relatively
high amount of tungsten.
A number of techniques may be used in the study of
acidity of solid catalysts, such as pyridine-IR, NH3-TPD
and NMR. The main drawback of NH3-TPD is not able
to distinguish between Brønsted acid and Lewis acid, as
well as their subtle differences in the distribution, while
pyridine-IR is very difficult to study acid density quan-
titatively. 31P MAS NMR with trimethylphosphine
(TMP) as the probe molecule has the advantages of dis-
tinguishable and assignable peaks and may provide
comprehensive information on the acid type, strength
distribution and relevant density.[47-50] Herein, the acid
property of Nb-W oxides was evaluated by 31P MAS
NMR spectroscopy using TMP as a probe molecule.
Results and Discussion
Physico-chemical properties of the catalysts
Nitrogen adsorption-desorption isotherms and the
pore size distribution of the Nb-W oxides are shown in
Figure 1. All the samples show the type IV isotherms
with a clear hysteresis loop, suggesting the presence of
typical mesopores. Table 1 and Figure 1b show that the
BET specific surface area decreased from 174 m2•g1 to
26 m2•g1 with the increase of tungsten content, accom-
Figure 1 (a) N2 adsorption-desorption isotherms of Nb-W oxides, (b) pore size distributions of Nb-W oxides.
Table 1 Characterization of the catalysts
Catalyst SBET/(m2•g1) Pore volume/(cm3•g1)
Pore diameter/nm
Brønsted acid/(µmol•g1)
Lewis acid/(µmol•g1)
B/L
0.31
0.62
1.83
1.26
Nb2O5
174
0.32
0.30
0.22
0.21
7.4
7.3
6.1
6.0
63
203
116
84
Nb9W1 152
Nb7W3 146
Nb5W5 126
72
154
112
89
Figure 2 TEM images of (a) Nb2O5, (b) Nb9W1, (c) Nb7W3 and (d) Nb5W5 oxides.
Chin. J. Chem. 2017, XX, 1—11
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
3

Guo et al.
FULL PAPER
There are three different types of adsorbed TMP as
shown in Scheme 1. TMP tends to form protonated ad-
ducts, giving rise to 31P resonances in a rather narrow
range of δ 2 to 5.[51] The chemical shift from δ 20 to
50 is assigned to TMP on Lewis acid sites, which is
more sensitive to the strength of Lewis acid than that of
Brønsted acid.[46] The 31P MAS NMR spectra of meso-
porous niobic oxide and Nb-W oxides are shown in
Figure 3. The broad peak at ca. δ 62 could be assigned
to trimethylphosphine oxide (TMPO) interacting with
Brønsted acid sites,[52] which was observed on all mes-
oporous niobic oxide and Nb-W oxides. The existence
of TMPO is possibly due to the oxidation of TMP on the
surface of mesoporous niobic oxide and Nb-W oxides.
The 31P chemical shifts of TMP on Lewis acid sites
tended to shift to high field (from δ 37.4 to 50.6) with
increasing tungsten content, indicating the created Lew-
is acid sites by addition of tungsten in niobium oxide are
usually weaker than the Lewis acid sites initially present
on the niobium oxides. It suggests that the addition of
tungsten in niobium oxide results in partial replacement
could be favored in aqueous system.[57]
Figure 3 31P MAS NMR spectra of (a) Nb2O5, (b) Nb9W1, (c)
＋
＋
of Nb5 ions by higher-valence W6 ions, leading to
increase of the number of Brønsted acid sites (as shown
in Table 1) formed by bridged hydroxyl groups
(Nb-(OH)-W). However, the slight decrease of Brønsted
acid sites of Nb5W5 oxide is mainly caused by decreas-
ing of surface area and possible formation of amorphous
surface polytungstate species with high amount of tung-
sten.[53,54] Lewis acid sites in Nb oxide are mostly gen-
erated from NbO4 tetrahedra and highly distorted NbO6
octahedra. It can be anticipated that the addition of
tungsten in niobium oxide generates more perfect octa-
hedra, with the decreasing of Lewis acid sites from 203
µmol/g of Nb2O5 to 89 µmol/g of Nb5W5 oxide.
Nb7W3 and (d) Nb5W5 adsorbed with TMP.
Figure 4a shows the glucose conversion as function
of reaction time for various Nb-W oxide catalysts. All
mesoporous Nb and Nb-W oxide catalysts show higher
glucose conversion compared to that of sulfuric acid
(SA) which has no Lewis acidity. On the other hand,
mineral acid SA shows glucose conversion of <10%
even after 360 min reaction. Therefore, it clearly indi-
cates that Lewis acidity plays a significant role in glu-
cose conversion. In general, the dehydration of glucose
to HMF proceeds through a tandem pathway including
isomerization of glucose to fructose over Lewis acid and
succeeding dehydration of fructose to HMF over
Brønsted acid.[2,25,30,58] Glucose conversion over all
three Nb-W oxides with different Nb/W ratios increases
in the order of Nb7W3＞Nb5W5＞Nb9W1, which is con-
sistent with the trend of the ratios of Brønsted to Lewis
acid sites (as shown in Table 1). Higher glucose conver-
sion was observed for Nb5W5 and Nb7W3 oxides which
have relatively high ratios of Brønsted to Lewis acid
sites.
Scheme 1 Three types of adsorbed trimethylphosphine: (a)
chemisorbed on Brønsted acid sites, (b) physisorbed on hydroxyls
(hydrogen bonding interaction) and (c) chemisorbed on Lewis
acid centers[46]
As mentioned above, the dehydration of glucose to
HMF is a tandem reaction including isomerization of
glucose to fructose and fructose dehydration to HMF.
Hence, the selectivity of fructose is expected to be rela-
tive with the balance of isomerization and dehydration.
As shown in Figure 4b, the fructose selectivities over all
catalysts are not higher than 4%, which are much lower
than those over solid acid catalysts such as mesoporous
tantalum oxide,[34] metal(IV) phosphates,[40] sulfated
zirconia[42] and combination of Amberlyst-15 and hy-
drotalcite.[59] The fructose selectivity over Nb2O5 de-
creases from 4% at 60 min to 1% after 360 min of the
reaction. At the same time, fructose could hardly be de-
tected over Nb5W5 and Nb7W3 oxide catalysts. The ab-
sence of fructose could be attribute to the fast dehydra-
Glucose dehydration in aqueous phase
It is well known that the transformation process of
glucose over heterogeneous catalysts is rather compli-
cated due to a number of parallel reactions.[40] As shown
in Scheme 2, glucose could be dehydrated to cellobiose
and levoglucosan; saccharides could polymerize with
reaction products containing aldehyde group such as
HMF and furfural, leading to forming water soluble
polymers and water insoluble humins;[55,56] subsequently,
rehydration of HMF to levulinic acid and formic acid
4
www.cjc.wiley-vch.de
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2017, XX, 1—11

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural
Scheme 2 Reaction pathway for conversion of saccharides to HMF
Sucrose
CH2OH
Rehydration products
CH2OH CH2OH
O
O
Levulininc acid
Formic acid
OH
OH
O
OH
O
OH
HO
OH
O
OH
H
+2H2O
O
OH
Acid Hydrolysis
O
+H2O
OH
CH2OH CH2OH
O
OH
O
-3H2O
O
O
O
OH
HO
HO
OH
OH
OH
D-fructose
HO
O
Furfural
HMF
D-glucose
H
H
Formaldehyde
-H2O
O
O
Levoglucosan
OH
HO
HO
OH
OH
O
HO
HO
O
O
OH
OH
Polymers and Humins
Condensation Products
HO
OH
Cellobiose
Reversion Products
Figure 4 Glucose conversion (a), selectivity to fructose (b), HMF (c) and acids (d) versus reaction time over different catalysts. Reac-
tion conditions: 0.1 g catalyst, 5 mL of 2 wt% D-glucose solution were stirred in an autoclave at 140 ℃.
tion of fructose to HMF over catalysts with more
Brønsted acid sites. These results could also be ex-
plained by another proposed mechanism which is suita-
ble for solid acid catalysts with both Brønsted acid sites
and Lewis acid sites, i.e. isomerization of glucose over
Lewis acid sites accompanied with dehydration to HMF
over Brønsted acid sites without intermediate desorption
of fructose molecules.[39]
The selectivity to HMF over different catalysts is
shown in Figure 4c. A similar trend of HMF selectivity
was observed for all catalysts. The HMF selectivity
firstly increased then decreased with increasing reaction
times, owing to rehydration of HMF to levulinic acid,
formic acid over Brønsted acid sites and condensation to
Chin. J. Chem. 2017, XX, 1—11
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
5

Guo et al.
FULL PAPER
soluble polymers and humins over Lewis acid
sites.[30,39,40,55] The HMF selectivity reached a maximum
value of 33% over Nb5W5 oxide after 240 min and 37%
over Nb7W3 oxide after 300 min. On the other hands,
the HMF selectivities over Nb2O5 and Nb9W1 oxides
with relatively high amount of Lewis acid sites achieve
their maximum value at longer reaction time than
Nb7W3 and Nb5W5 oxides with high amount of
Brønsted acid sites. No HMF was observed for pure SA,
possibly due to low yield of HMF and easy hydration of
HMF with mineral acid in aqueous catalysis system,
which could be confirmed by low conversion of glucose
and low selectivity of fructose over SA.
The selectivity to levulinic acid and formic acid is
shown in Figure 4d. A relatively higher acids selectivity
was observed for SA in comparison with Nb-W oxide
catalysts, ascribing to easier rehydration of HMF to le-
vulinic acid and formic acid over SA with only Brønsted
acidity. This is in agreement with the results over alu-
minum phosphate and titanium phosphate catalysts,[39]
where high selectivity to acids was found to become
more significant when the catalyst has a low activity in
the dehydration of the more stable glucose molecule.
For SA, the selectivity to acids increased fast to 51%
after 240 min reaction time at glucose conversion even
below 10%. At the same time, no HMF was observed
due to the low conversion of glucose and easy rehydra-
tion of HMF over mineral acid in aqueous catalytic sys-
tem. In contrast, the selectivity to acids over Nb-W ox-
ide catalysts was in the range of 3%－7% even after 360
min reaction time.
On the basis of our results above, it possibly en-
lightens us on design and preparation of solid acid cata-
lysts for effective conversion of glucose to HMF. Our
results demonstrate clearly the importance and necessity
of both Brønsted and Lewis acid sites in an effective
catalyst. First, the activation of glucose molecule occurs
preferentially over Lewis acid sites. Thus, in order to
obtain a considerable conversion of glucose, catalysts
with Lewis acidity other than pure SA should be chosen.
Once glucose isomerization succeeds over Lewis acid
sites, formed fructose needs to be dehydrated to HMF
by Brønsted acid. However, the existence of side-reac-
tions, such as condensation of sugars and HMF over
Lewis acid sites[30,39,40,55] and rehydration of HMF over
Brønsted acid sites, demands the suitable ratios of
Brønsted to Lewis acid sites which in turn achieves high
selectivity to HMF.
It is noteworthy that the mass balance is not satisfied
on all Nb-W oxide catalysts after summation of the se-
lectivity of all detected main products like fructose, ac-
ids and HMF. Approximately 50%－60% of glucose is
transformed into humins, which cannot be detected by
HPLC and GC-MS. In general, humins were considered
as all unidentified water soluble and insoluble polymers.
The formation of humins can be mainly attributed to the
aldol condensation of HMF and unreacted saccharides
with formyl groups (－CHO) in the presence of acid
catalysts.[60,61] Thus, the selectivity of HMF can be the-
oretically improved by using a biphasic system, where
the formed HMF may be dissolved in the organic phase
and separated from the aqueous media containing unre-
acted saccharides for suppression of HMF rehydration
and condensation with saccharides.[18]
Glucose dehydration in 2-butanol/H2O system
As far as we know, various organic solvents have
been used in biphasic system for conversion of saccha-
rides to HMF. Among them, solvents with four carbon
atoms (C4) like 2-butanol were commonly used and
showed the highest affinity for HMF, coupled with low
water miscibility at the reaction temperature.[9,10,12,33] In
the present case, we also studied the performances of
other organic solvents such as THF, MIBK, DMSO at
first. 2-Butanol and MIBK exhibited similar high value
of HMF selectivity. However, MIBK has a higher HMIS
health hazard rating than 2-butanol,[24] thus 2-butanol
was chosen in consideration of enviromental impact and
cost-effective chemical principle. Further glucose dehy-
dration studies were carried out with mesoporous Nb2O5
in a 2-butanol/H2O system, where the yields of fructose
and acids were extremely low, and therefore, we fo-
cused on only production of HMF.
The influence of solvent dosage on the glucose con-
version as well as the selectivity to HMF was investi-
gated. Figure 5 shows glucose dehydration over niobi-
um oxide in the presence of different dosage of
2-butanol. Extraction of HMF by 2-butanol, which is
visible by a colorless aqueous phase and a brown or-
ganic phase, shows a clear water/oil interface in Figure
S1a†. Without an addition of 2-butanol, the selectivity
to HMF is 35% at nearly 100% glucose conversion. Af-
ter the addition of 2-butanol (2-butanol/H2O＝2∶2,
V/V) the selectivity significantly increases to 41%. The
catalytic results reflect that the selectivity of HMF can
be improved by adding 2-butanol for distracting the
formed HMF from catalyst surface and suppressing fur-
ther rehydration and condensation of HMF. It is notice-
able that the water/oil interface disappears with increas-
ing the 2-butanol/H2O ratio to 5∶2 (V/V) since pure
2-butanol is partially miscible with water.[12] However,
at a 2-butanol/H2O ratio of 5∶2 (V/V), the selectivity to
HMF keeps at about 42%. This high HMF selectivity is
possibly due to improving activity of the catalyst by
removing humins deposed on the surface of the catalyst
with organic solvent. However, the addition of exces-
sive 2-butanol (2-butanol/H2O＝7∶2, V/V) may lead to
desorption of fructose from active sites which accounts
for the decreasing HMF selectivity.
The influence of the reaction temperature has been
investigated at a 5∶2 V/V ratio of 2-butanol/H2O. As
shown in Figure 6, at low temperature of 80 ℃ and
100 ℃, only 5% and 17% of HMF selectivity can be
obtained, respectively. As the apparent activation energy
associated with the HMF formation from fructose is
higher compared with that of glucose isomerization,[30]
6
www.cjc.wiley-vch.de
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2017, XX, 1—11

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural
catalytic reaction.
Figure 7 shows the catalytic performance with dif-
ferent reaction time. The reaction is extremely fast, as
75% of glucose conversion was achieved after 30 min.
In the 2-butanol/H2O system, the addition of 2-butanol
leads to a fast transformation of glucose to HMF due to
the equilibrium shifts towards the HMF formation by
partitioning of HMF from sugar reactants. Similar ob-
servations were obtained in previous studies where solid
metal phosphate catalysts with relatively high Brønsted
to Lewis ratios were used.[33-35,37,40] These results
demonstrate that the first step of glucose isomerization
is very fast, and formed intermediates may occupy some
active sites initially which could slow down subsequent
reaction. The selectivity to HMF increases with the re-
action time, attaining the maximum value of 42% after 2
h. However, further prolonging reaction time causes
slight decrease of HMF selectivity, possibly due to the
preferential rehydration of HMF in aqueous media or
condensation of HMF (Figure S1c†). Thus, 2 h was se-
lected as the optimal reaction time.
Figure 5 Comparison of different ratios of 2-butanol/H2O for
the conversion of glucose into HMF over Nb2O5. 0.2 g of catalyst,
2 mL of 1 wt% D-glucose and desired volume of 2-butanol were
stirred in an autoclave at 140 ℃ for 2 h.
Figure 6 Comparison of different reaction temperature for the
conversion of glucose into HMF over Nb2O5. 0.2 g of catalyst, 2
mL of 1 wt% D-glucose and 5 mL of 2-butanol (2-butanol/H2O＝
5∶2, V/V) were stirred in an autoclave at set temperature for 2 h.
Figure 7 Comparison of different reaction time for the conver-
sion of glucose into HMF over Nb2O5. 0.2 g of catalyst, 2 ml of 1
wt% D-glucose and 5 mL of 2-butanol (2-butanol/H2O＝5∶2,
V/V) were stirred in an autoclave at 140 ℃.
only 3% of HMF yield was achieved at 80 ℃ with
more than 55% of glucose conversion. In addition, only
a small amount of fructose can be detected, which is
very common in the published studies of glucose dehy-
dration to HMF over an effective solid acid
catalyst.[32,34,37-39,41] Since there are many parallel reac-
tions in the transformation process of glucose over solid
acid catalysts, the formation of a number of reversion
and epimerization intermediates such as mannose and
enediol could increase the glucose transforma-
tion.[25,40,41,61] With increasing reaction temperature to
120 ℃, the HMF yield increases up to 35% with 95%
of glucose conversion and the selectivity of HMF in-
creases slowly above 120 ℃. The catalytic results re-
flect that glucose conversion and HMF selectivity in-
crease with increasing reaction temperature, achieving
the highest values at 140 ℃. At higher reaction temper-
ature, the side reactions such as HMF rehydration and
condensation result in the decrease of HMF selectivity.
Thus, 140 ℃ was selected as the optimized reaction
temperature to study other parameters influencing the
Figure 8 shows the catalytic performance with dif-
ferent catalyst dosage for the conversion of glucose into
HMF. With only 0.05 g of Nb2O5, 90% of glucose con-
version and 27% of HMF selectivity are obtained.
However, without addition of Nb2O5, glucose conver-
sion is only 15%. With increasing dosages of catalyst to
more than 0.1 g, almost 100% conversion of glucose is
obtained. Regarding the selectivity of HMF, it monoto-
nously increases with increasing the dosages of catalyst
and achieves the maximum value (42%) with 0.2 g of
catalyst. However, beyond 0.2 g of catalyst the selectiv-
ity of HMF can hardly be improved and remains ap-
proximately 40%.
The glucose conversion and HMF selectivity de-
crease when the initial glucose concentration increases
from 1 wt% to 10 wt% (Figure 9). The change of HMF
selectivity is in agreement with literature reports that
increasing the initial saccharide concentration leads to
Chin. J. Chem. 2017, XX, 1—11
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
7

Guo et al.
FULL PAPER
the results of six consecutive runs over both catalysts.
Between each run, the catalyst was simply recovered by
washing with 10 mL of deionized water three times be-
fore drying at 120 ℃ for 2 h. In the consecutive ex-
periments no significant decreases in conversion and
selectivity were observed. The reusability of the present
catalysts is better than the reported results where the
apparent loss of catalytic activity was observed due to
the blockage of acid sites by formed humins.[35,38,42,43]
Moreover, in the conversion of glucose with the similar
Nb-W oxide catalyst in aqueous system at 120 ℃, Guo
et al. still found noticeable decrease of catalytic perfor-
mance even after re-calcination of Nb4W4 under 400 ℃
for 4 h to remove residue.[44] This clearly reveals that
the 2-butanol/H2O system enhances the HMF selectivity
and stabilizes the activity of the catalysts. Therefore, it
can be concluded that the Nb and Nb-W oxide catalysts
are effective catalysts for the conversion of glucose to
HMF in a 2-butanol/H2O system. Among them, Nb-W
oxide catalyst shows better catalytic performance.
Figure 8 Comparison of different catalyst dosage for the con-
version of glucose into HMF. Nb2O5 was used as catalyst, 2 mL
of 1 wt% D-glucose and 5 mL of 2-butanol (2-butanol/H2O＝5∶
2, V/V) were stirred in an autoclave at 140 ℃ for 2 h.
Figure 9 Comparison of different glucose concentration for the
conversion of glucose into HMF over Nb2O5. 0.2 g of catalyst, 2
mL of 1 wt% D-glucose and 5 mL of 2-butanol (2-butanol/H2O＝
5∶2, V/V) were stirred in an autoclave at 140 ℃.
Figure 10 Reuse of Nb2O5 and Nb7W3 oxide for the conversion
of glucose into HMF. 0.2 g of catalyst, 2 mL of 1 wt% D-glucose
and 5 mL of 2-butanol (2-butanol/H2O＝5∶2, V/V) were stirred
in an autoclave at 140 ℃ for 2 h.
high probability of side reactions between fructose and
HMF.[61,62] However, it should be noted that the de-
crease of HMF selectivity is larger than that of glucose
conversion. Although high catalytic activity (92% con-
version of glucose) is maintained with 10 wt% of initial
glucose concentration, excessive unreacted glucose and
formed HMF exist, leading to side reactions such as
condensation and rehydration which are favored in
aqueous media. In Figure S1e† one may see the color of
reaction liquids changes from light brown to dark with
increasing the initial glucose concentration from 1 wt%
to 10 wt%, in agreement with the formation of more
soluble polymers and humins at higher initial glucose
concentration. Thus, it can be deduced from Figure 9
that, catalytic system with low initial glucose concentra-
tion could be used to minimize side reactions of HMF
and sugars. For this reason, high glucose concentrations
may not be advisable in a one-pot catalytic system.
A further investigation of mesoporous Nb and Nb-W
oxide along with other relevant catalysts in the conver-
sion of sugars such as glucose, fructose and sucrose into
HMF in the 2-butanol/H2O catalytic system is shown in
Table 2. The selectivity of HMF from fructose, which is
highly determined by the amount of Brønsted acid sites
on catalyst, is in the order of Nb2O5•nH2O≈Nb5W5≈
Nb7W3 ＞Nb9W1 ＞Nb2O5 ＞blank. These results are
consistent with the acidity characterization of Nb and
Nb-W oxides in this work by solid state 31P MAS NMR
and the fact that Nb2O5•nH2O has abundance of
Brønsted acid sites.
Although there is a well-known fact that keto-hex-
oses produce higher yields of HMF compared to al-
do-hexoses,[62] it is interesting to note that glucose con-
version over Nb2O5 and Nb-W oxides proceeds higher
With the optimized reaction conditions in the
2-butanol/H2O system, the reusability of Nb2O5 and
Nb7W3 oxide catalysts was evaluated. Figure 10 depicts
8
www.cjc.wiley-vch.de
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2017, XX, 1—11

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural
Table 2 Results for the conversion of sugars using different catalystsa
Substrate
Fructose
Catalyst
Conversion/mol%
HMF yield/mol%
HMF selectivity/mol%
Nb2O5
＞99
＞99
＞99
＞99
＞99
16
28
33
39
40
42
2
28
33
39
40
42
13
Nb9W1
Nb7W3
Nb5W5
Nb2O5•nH2O
No catalyst
Glucose
Sucrose
Nb2O5
＞99
＞99
＞99
96
42
47
52
44
13
2
42
47
52
46
23
13
Nb9W1
Nb7W3
Nb5W5
Nb2O5•nH2O
No catalyst
56
15
Nb2O5
＞99
＞99
＞99
＞99
74
36
42
45
46
13
2
36
42
45
46
18
6
Nb9W1
Nb7W3
Nb5W5
Nb2O5•nH2O
No catalyst
31
a Reaction conditions: 0.2 g of catalyst, 2 mL of 1 wt% sugar and 5 mL of 2-butanol (2-butanol/H2O＝5∶2, V/V) were stirred in an auto-
clave at 140 ℃ for 2 h.
HMF selectivity than those from fructose. The results in
Table 2 show that the highest selectivity of HMF from
glucose is achieved by using Nb7W3 oxide catalyst, ap-
proaching 52% with almost 100% glucose conversion in
comparison with 39% HMF selectivity from fructose in
the same reaction conditions. This observation suggests
that unselective condensation of fructose and HMF is
favored over catalysts with relatively high density of
Lewis acid sites such as Nb2O5, since only Nb2O5•nH2O
was found to induce higher selectivity of HMF for fruc-
tose (42%) than glucose (23%). As for HMF formation
from glucose, continuous formation of fructose by glu-
cose isomerization on Lewis acid sites and further de-
hydration of fructose to HMF on Brønsted acid sites
keep the concentration of formed fructose relatively low,
which minimizes undesired reaction like cross-
polymerization of fructose and HMF or condensation of
unreacted fructose on Lewis acid sites. Moreover, when
sucrose was employed as the substrate, the conversion
of sucrose follows the selectivity trends for the conver-
sion of glucose or fructose, which is due to that sucrose
behaves as the 1∶1 mixture of fructose and glucose. In
general, when using Nb2O5 and Nb-W oxides as the
catalysts, the selectivity of HMF from sucrose is slightly
lower than that from glucose under the same reaction
conditions because sucrose should be firstly hydrolyzed
to form equimolar glucose and fructose. In contrast,
Nb2O5•nH2O with predominant Brønsted acidity does
not improve the selectivity of HMF for the conversions
of sucrose (18%) and glucose (23%), revealing that
isomerization of glucose is the rate-determining step for
HMF formation. This result is in agreement with the
work of Domen and co-workers,[54] where they found
niobic acid showed low activity in sucrose hydration.
In all cases, the sugar conversion and the selectivity
of HMF without catalyst achieve the minimum value,
indicating that the solid acid catalyst plays a pivotal role
in HMF formation from sugar. Mesoporous Nb and
Nb-W oxides show effective catalytic activities for
HMF formation from sugars such as glucose, fructose
and sucrose. Furthermore, it reveals that the 2-butanol/
H2O catalytic system with acid Nb-W oxide catalysts
could also be applied in the direct formation of HMF
from other inexpensive and abundantly available re-
newable feedstocks through their hydration to mono-
saccharides.
Conclusions
In summary, a series of mesoporous Nb and Nb-W
oxides were prepared and employed as highly catalytic
active, recyclable solid acid catalysts for the conversion
of glucose to HMF. Solid state 31P MAS NMR spectro-
scopic study with TMP as the probe molecule reveals
that the addition of tungsten in niobium oxide increases
the number of Brønsted acid sites and decreases the
number of Lewis acid sites.
The dehydration of glucose in aqueous medium is
achieved by tandem reactions including isomerization of
glucose to fructose over Lewis acid sites and fructose
dehydration to HMF over Brønsted acid sites. The cata-
lytic activity and selectivity for all Nb-W oxides vary
Chin. J. Chem. 2017, XX, 1—11
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
9

Guo et al.
FULL PAPER
2014, 2, 978.
according to the ratios of Brønsted to Lewis acid sites.
Higher glucose conversion was achieved over Nb5W5
and Nb7W3 oxides with relatively high ratios of
Brønsted to Lewis acid sites.
[23] Song, C.; Liu, H.; Li, Y.; Ge, S.; Wang, H.; Zhu, W.; Chang, Y.; Han,
C.; Li, H. Chin. J. Chem. 2014, 32, 434.
[24] Pagan-Torres, Y. J.; Wang, T.; Gallo, J. M. R.; Shanks, B. H.;
Dumesic, J. A. ACS Catal. 2012, 2, 930.
The selectivity of HMF can be further improved
with a 2-butanol/H2O system. The organic phase may
extract formed HMF from the aqueous phase, thus sup-
pressing HMF rehydration and condensation, leading to
high stable catalytic activity of Nb and Nb7W3 oxides.
Among those catalysts studied, Nb7W3 oxide exhibits
＞99% conversion of glucose and 52% HMF selectivity.
Moreover, this catalytic system can also be extended to
conversion of sucrose, achieving high HMF selectivity
of 45%－46% over Nb7W3 and Nb5W5 oxides.
[25] Roman-Leshkov, Y.; Moliner, M.; Labinger, J. A.; Davis, M. E. An-
gew. Chem., Int. Ed. 2010, 49, 8954.
[26] Zhao, H.; Holladay, J. E.; Brown, H.; Zhang, Z. C. Science 2007,
316, 1597.
[27] Wang, T. F.; Pagan-Torres, Y. J.; Combs, E. J.; Dumesic, J. A.;
Shanks, B. H. Top. Catal. 2012, 55, 657.
[28] Dutta, S.; De, S.; Alam, M. I.; Abu-Omar, M. M.; Saha, B. J. Catal.
2012, 288, 8.
[29] Deng, T.; Cui, X.; Qi, Y.; Wang, Y.; Hou, X.; Zhu, Y. Chem. Com-
mun. 2012, 48, 5494.
[30] Choudhary, V.; Mushrif, S. H.; Ho, C.; Anderko, A.; Nikolakis, V.;
Marinkovic, N. S.; Frenkel, A. I.; Sandler, S. I.; Vlachos, D. G. J. Am.
Chem. Soc. 2013, 135, 3997.
[31] Chan, J. Y. G.; Zhang, Y. ChemSusChem 2009, 2, 731.
[32] Nakajima, K.; Baba, Y.; Noma, R.; Kitano, M.; Kondo, J. N.;
Hayashi, S.; Hara, M. J. Am. Chem. Soc. 2011, 133, 4224.
[33] Yang, F.; Liu, Q.; Yue, M.; Bai, X.; Du, Y. Chem. Commun. 2011, 47,
4469.
[34] Jimenez-Morales, I.; Moreno-Recio, M.; Santamaria-Gonzalez, J.;
Maireles-Torres, P.; Jimenez-Lopez, A. Appl. Catal., B 2014, 154－
155, 190.
[35] Jimenez-Morales, I.; Teckchandani-Ortiz, A.; Santamaria-Gonzalez,
J.; Maireles-Torres, P.; Jimenez-Lopez, A. Appl. Catal., B 2014, 144,
22.
[36] Corma, A.; Renz, M. Chem. Commun. 2004, 550.
[37] Nakajima, K.; Noma, R.; Kitano, M.; Hara, M. J. Mol. Catal.
A-Chem. 2014, 388, 100.
[38] Yan, H.; Yang, Y.; Tong, D.; Xiang, X.; Hu, C. Catal. Commun. 2009,
10, 1558.
[39] Ordomsky, V. V.; Sushkevich, V. L.; Schouten, J. C.; van der Schaaf,
J.; Nijhuis, T. A. J. Catal. 2013, 300, 37.
[40] Weingarten, R.; Kim, Y. T.; Tompsett, G. A.; Fernandez, A.; Han, K.
S.; Hagaman, E. W.; Conner, W. C.; Dumesic, J. A.; Huber, G. W. J.
Catal. 2013, 304, 123.
[41] Noma, R.; Nakajima, K.; Kamata, K.; Kitano, M.; Hayashi, S.; Hara,
M. J. Phys. Chem. C 2015, 119, 17117.
[42] Osatiashtiani, A.; Lee, A. F.; Brown, D. R.; Melero, J. A.; Morales,
G.; Wilson, K. Catal. Sci. Technol. 2014, 4, 333.
[43] Zhang, Y.; Wang, J. J.; Ren, J. W.; Liu, X. H.; Li, X. C.; Xia, Y. J.;
Lu, G. Z.; Wang, Y. Q. Catal. Sci. Technol. 2012, 2, 2485.
[44] Guo, J.; Zhu, S. H.; Cen, Y. L.; Qin, Z. F.; Wang, J. G.; Fan, W. B.
Appl. Catal., B 2017, 200, 611.
Acknowledgement
This work was supported by the National Natural
Science Foundation of China (Nos. 21173050,
21371035) and China Petrochemical Corporation (No.
X514005).
References
[1] Tuck, C. O.; Perez, E.; Horvath, I. T.; Sheldon, R. A.; Poliakoff, M.
Science 2012, 337, 695.
[2] Chheda, J. N.; Huber, G. W.; Dumesic, J. A. Angew. Chem., Int. Ed.
2007, 46, 7164.
[3] Lange, J.-P.; Price, R.; Ayoub, P. M.; Louis, J.; Petrus, L.; Clarke, L.;
Gosselink, H. Angew. Chem., Int. Ed. 2010, 49, 4479.
[4] Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107, 2411.
[5] Serrano-Ruiz, J. C.; Luque, R.; Sepulveda-Escribano, A. Chem. Soc.
Rev. 2011, 40, 5266.
[6] Carlos Serrano-Ruiz, J.; Dumesic, J. A. Energy Environ. Sci. 2011, 4,
83.
[7] Roman-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Nature
2007, 447, 982.
[8] Hara, M.; Nakajima, K.; Kamata, K. Sci. Technol. Adv. Mater. 2015,
16, 034903.
[9] 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.
[10] Rosatella, A. A.; Simeonov, S. P.; Frade, R. F. M.; Afonso, C. A. M.
Green Chem. 2011, 13, 754.
[11] Teong, S. P.; Yi, G. S.; Zhang, Y. G. Green Chem. 2014, 16, 2015.
[12] Roman-Leshkov, Y.; Chheda, J. N.; Dumesic, J. A. Science 2006,
312, 1933.
[13] Zakrzewska, M. E.; Bogel-Łukasik, E.; Bogel-Łukasik, R. Chem.
Rev. 2011, 111, 397.
[14] Buntara, T.; Noel, S.; Phua, P. H.; Melian-Cabrera, I.; de Vries, J. G.;
Heeres, H. J. Angew. Chem., Int. Ed. 2011, 50, 7083.
[15] Patel, A. D.; Serrano-Ruiz, J. C.; Dumesic, J. A.; Anex, R. P. Chem.
Eng. J. 2010, 160, 311.
[16] Kourieh, R.; Rakic, V.; Bennici, S.; Auroux, A. Catal. Commun.
2013, 30, 5.
[17] De, S.; Dutta, S.; Saha, B. Green Chem. 2011, 13, 2859.
[18] Ordomsky, V. V.; van der Schaaf, J.; Schouten, J. C.; Nijhuis, T. A. J.
Catal. 2012, 287, 68.
[19] Shi, C.; Zhao, Y.; Xin, J.; Wang, J.; Lu, X.; Zhang, X.; Zhang, S.
Chem. Commun. 2012, 48, 4103.
[20] Qi, X.; Watanabe, M.; Aida, T. M.; Smith, R. L., Jr. Green Chem.
2009, 11, 1327.
[21] Song, J.; Zhang, B.; Shi, J.; Ma, J.; Yang, G.; Han, B. Chin. J. Chem.
2012, 30, 2079.
[45] Ye, L.; Xie, S. H.; Yue, B.; Qian, L. P.; Feng, S. J.; Tsang, S. C.; Li,
Y. C.; He, H. Y. CrystEngComm 2010, 12, 344.
[46] Chu, Y.; Yu, Z.; Zheng, A.; Fang, H.; Zhang, H.; Huang, S.-J.; Liu,
S.-B.; Deng, F. J. Phys. Chem. C 2011, 115, 7660.
[47] Zheng, A.; Huang, S.-J.; Liu, S.-B.; Deng, F. Phys. Chem. Chem.
Phys. 2011, 13, 14889.
[48] Shimizu, K.; Venkatraman, T. N.; Song, W. G. Appl. Catal., A 2002,
224, 77.
[49] Chen, W. H.; Ko, H. H.; Sakthivel, A.; Huang, S. J.; Liu, S. H.; Lo,
A. Y.; Tsai, T. C.; Liu, S. B. Catal. Today 2006, 116, 111.
[50] Haw, J. F.; Zhang, J. H.; Shimizu, K.; Venkatraman, T. N.; Luigi, D.
P.; Song, W. G.; Barich, D. H.; Nicholas, J. B. J. Am. Chem. Soc.
2000, 122, 12561.
[51] Lunsford, J. H.; Rothwell, W. P.; Shen, W. J. Am. Chem. Soc. 1985,
107, 1540.
[52] Rakiewicz, E. F.; Peters, A. W.; Wormsbecher, R. F.; Sutovich, K. J.;
Mueller, K. T. J. Phys. Chem. B 1998, 102, 2890.
[53] Ross-Medgaarden, E. I.; Knowles, W. V.; Kim, T.; Wong, M. S.;
Zhou, W.; Kiely, C. J.; Wachs, I. E. J. Catal. 2008, 256, 108.
[22] Eminov, S.; Wilton-Ely, J.; Hallett, J. P. ACS Sustain. Chem. Eng.
10
www.cjc.wiley-vch.de
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2017, XX, 1—11

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5-Hydroxymethylfurfural
[54] Tagusagawa, C.; Takagaki, A.; Iguchi, A.; Takanabe, K.; Kondo, J.
N.; Ebitani, K.; Hayashi, S.; Tatsumi, T.; Domen, K. Angew. Chem.,
Int. Ed. 2010, 49, 1128.
[58] Nagorski, R. W.; Richard, J. P. J. Am. Chem. Soc. 2001, 123, 794.
[59] Ohara, M.; Takagaki, A.; Nishimura, S.; Ebitani, K. Appl. Catal., A
2010, 383, 149.
[55] Ordomsky, V. V.; Van Der Schaaf, J.; Schouten, J. C.; Nijhuis, T. A.
ChemSusChem 2012, 5, 1812.
[60] Antal Jr, M. J.; Mok, W. S. L.; Richards, G. N. Carbohyd. Res. 1990,
199, 91.
[56] Xiang, Q.; Lee, Y. Y.; Torget, R. W. Appl. Biochem. Biotech. 2004,
113－116, 1127.
[61] van Dam, H. E.; Kieboom, A. P. G.; van Bekkum, H. Starch/Stärke
1986, 38, 95.
[57] Kuster, B. F. M. Carbohyd. Res. 1977, 54, 177.
[62] Kuster, B. F. M. Starch/Stärke 1990, 42, 314.
(Cheng, F.)
Chin. J. Chem. 2017, XX, 1—11
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
11