Efficient and selective conversion of hexose to 5-hydroxymethylfurfural with tin-zirconium-containing heterogeneous catalysts

Article abstract of DOI:10.1016/j.catcom.2014.02.023

Efficient and selective production of 5-hydroxymethylfurfural (HMF) from the hexose is achieved in the presence of heterogeneous Sn-based catalyst. The mixed SnO₂-ZrO₂ is prepared from zirconium n-propoxide and different metal Sn precursors using Sol-gel method. The sulfated SnO ₂-ZrO₂ (SO₄^{2 -}/SnO ₂-ZrO₂) is obtained by the impregnation method with H ₂SO₄ solution. All catalytic materials are detected with XRD, TG, SEM, TEM and BET techniques in order to reveal the physical properties and structures of these materials. When these materials were used in the dehydration of fructose, it was found that the suitable ratio of Sn/Zr is 0.5, and the catalytic activity of SO₄^{2 -}/SnO ₂-ZrO₂ is higher than that of SnO₂-ZrO ₂ where more than 75.0% yield of HMF was obtained for 2.5 h at 120 C. The effects of reaction temperature and reaction time were also investigated. Moreover, the recycling experiment of catalyst shows that the catalytic activity can be almost kept unchanged after being used five times.

Full text of DOI:10.1016/j.catcom.2014.02.023

Catalysis Communications 50 (2014) 38–43
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Catalysis Communications
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Short Communication
Efficient and selective conversion of hexose to 5-hydroxymethylfurfural
with tin–zirconium-containing heterogeneous catalysts
1
1
1
1
⁎
Yanhua Wang , Xinli Tong , Yongtao Yan , Song Xue , Yangyang Zhang
Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry & Chemical Engineering, Tianjin University of Technology, Tianjin 300384, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient and selective production of 5-hydroxymethylfurfural (HMF) from the hexose is achieved in the presence
of heterogeneous Sn-based catalyst. The mixed SnO2–ZrO2 is prepared from zirconium n-propoxide and different
metal Sn precursors using Sol–gel method. The sulfated SnO2–ZrO2 (SO24−/SnO2–ZrO2) is obtained by the impreg-
nation method with H2SO4 solution. All catalytic materials are detected with XRD, TG, SEM, TEM and BET tech-
niques in order to reveal the physical properties and structures of these materials. When these materials were
used in the dehydration of fructose, it was found that the suitable ratio of Sn/Zr is 0.5, and the catalytic activity
of SO24−/SnO2–ZrO2 is higher than that of SnO2–ZrO2 where more than 75.0% yield of HMF was obtained for
2.5 h at 120 °C. The effects of reaction temperature and reaction time were also investigated. Moreover, the
recycling experiment of catalyst shows that the catalytic activity can be almost kept unchanged after being
used five times.
Received 31 January 2014
Received in revised form 24 February 2014
Accepted 25 February 2014
Available online 4 March 2014
Keywords:
Fructose
Dehydration
Tin
5-Hydroxymethylfurfural
Biomass conversion
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Using liquid acids as catalysts, various researches have been per-
formed on the catalytic dehydration of different hexoses [3,12–14].
In the past decades, fossil resources containing oil, natural gas and
coal had been considered as the important origins of energy and high-
value fine chemical; however, along with the increasingly environmen-
tal pollution and energy crises in recent years, renewable biomass feed-
stock and its further applications have attracted many scientists' great
attentions [1,2]. In chemistry field, an increasing effort has been devoted
to the catalytic transformation of biomass resources to the value-added
fine chemicals and biofuels [3–5]. As a potential alternative route, the
selective conversion of sugars to valuable chemicals become more and
more important in the chemical processing from biomass resources.
Therein, the production of furans from carbohydrates has been broadly
studied [6], in which 5-hydroxymethylfurfural (HMF), a dehydration
production of hexoses, is one of the important chemical intermediates
and platform chemicals [7]. Considering the molecular structure, HMF
is often used for preparing high density liquid fuel 2,5-dimethylfuran
(DMF) or polymeric monomer furan-2,5-dicarboxylic acid (FDCA) as
the raw material [8,9]. Also, the HMF had great potential to serve as a
substitute for the preparation of non-petroleum-derived building
blocks that were used in the production of polyamide and more fine
products [10]. Thus, developing a novel and efficient catalytic system
for the dehydration of sugars to HMF has gradually been a hot topic [11].
Therein, Antal and Mok [12] reported the catalytic dehydration of fruc-
tose with H2SO4 as a catalyst in the subcritical water at 250 °C, and a 53%
yield of HMF was gained. Domestic's group reported the production of
HMF from D-fructose in a biphasic reactor system, in which hydrochloric
acid was employed as the catalyst and MIBK–2-butanol mixture was
chosen as organic phase. After optimization, the selectivity of HMF
could reach 89% at high fructose conversion [3,13]. Furthermore, a
HMF yield of 60% was achieved at 92% fructose conversion and a HMF
selectivity of 65% using B(OH)3 and sodium chloride as catalyst in the
aqueous phase and methyl-isobutylketone (MIBK) as extracting solvent
[15]. Except for inorganic acids, metal halides were also employed as the
catalysts for the production of HMF [16–23]. For example, CrCl2 is found
to be uniquely effective in 1-alkyl-3-methylimidazolium chloride, leading
to the conversion of hexoses to HMF with a yield over 70% [16]. Moreover,
Yong et al. [17] found that more than 81% yield of HMF was respectively
achieved in the dehydration of hexoses with a NHC–Cr/ionic liquid sys-
tem at 100 °C for 6 h in the air. Also, Seri et al. [18] found that lanthanide
(III) could efficiently catalyze the dehydration of hexoses to HMF in H2O
at 140 °C. Hu et al. [19] revealed that SnCl4 could efficiently promote the
conversion of hexoses to HMF in [BMIM]BF4 ionic liquid and the yield is
as high as 61%. Furthermore, our group also reported that a combination
of FeCl3 and tetraethyl ammonium bromide is the efficient catalyst for the
dehydration of fructose in which that about 86% HMF yield was achieved
at full conversion of fructose [21]. We also found that a 73.8% yield of
HMF from fructose and a 69.1% yield of HMF from glucose were obtained
with SnCl4 and tetrabutyl ammonium bromide in DMSO for 2 h at 100 °C
[22].
⁎
Corresponding author at: Key Laboratory of Organic Solar Cells and Photochemical
Conversion, School of Chemistry and Chemical Engineering, Tianjin University of
Technology, No. 391, Binshuixi Road, Tianjin 300384, PR China. Tel./fax: + 86 22
60214259.
E-mail addresses: tongxinli@tju.edu.cn, tongxli@hotmail.com (X. Tong).
Tel./fax: +86 22 60214259.
1
http://dx.doi.org/10.1016/j.catcom.2014.02.023
1566-7367/© 2014 Elsevier B.V. All rights reserved.

Y. Wang et al. / Catalysis Communications 50 (2014) 38–43
39
Compared to liquid acid catalysts and metal chlorides, the solid acid
catalysts have the following advantages: (a) they facilitate the separa-
tion of product and can be recycled; (b) they can work at high temper-
atures, thus shortening the reaction time and favoring the formation of
HMF instead of its decomposition during a prolonged reaction period;
and (c) they are capable of adjusting the surface acidity to improve
the selectivity of HMF, which will be very useful to the conversion
of polysaccharides and biomass feedstocks [23]. Therein, the
heterogeneous catalysts such as alumina [24], aluminosilicate [25],
zirconium phosphate [26], niobic acid [27], ion-exchange resin
Amberlyst-15 [28], and zeolite [29,30] have been investigated in the
catalytic and selective conversion of different carbohydrates, and the
promising results were gained. Very recently, a solid heteropolyacid
Cs2.5H0.5PW12O40 has been used as catalyst in the converting fructose
to HMF, in which a 74.0% yield and 94.7% selectivity of HMF was obtain-
ed in 60 min at 115 °C [31]. Furthermore, Smith's group and Qi's group
reported the dehydration of fructose to HMF with the sulfated zirconia
under mild conditions. As a result, 72.8% or 88.4% yield of HMF in
the high conversion was respectively obtained in acetone–
dimethylsulfoxide mixtures [32] or 1-butyl-3-methyl imidazolium
chloride [33]. Moreover, Ning et al. [34] reported that the yield of
HMF could reach 86.5% in 1-ethyl-3-methylimidazolium bromide with
tin(IV) phosphonate as the catalyst which was obtained from the reac-
tion of SnCl4·5H2O and N,N-bis(phosphonomethyl) aminoacetic acid.
However, these catalytic systems have some disadvantages: either the
reaction is performed with expensive ionic liquids as the solvents, or
the preparation of catalyst is complicate. Thus, developing the efficient
and simple catalytic process for synthesis of HMF from carbohydrate
keeps a challenge.
b) Synthesis of sulfated SnO2–ZrO2 (SO24−/SnO2–ZrO2): the prepared
DZ-05 and TZ-05 are respectively placed in 1 M H2SO4 solution
and kept for 12 h under stirring. Then the obtained solid is further
dried at 100 °C overnight. Herein, sulfated SnO2–ZrO2 from DZ-05
and TZ-05 is written as SDZ-05 and STZ-05.
2.3. Catalyst characterization
The measurement of X-ray diffraction (XRD) was performed by
diffractometer with Cu Ka radiation source at 35 kV, 40 mA (0.02° reso-
lution) and was collected from 10 to 80° [2θ]. The morphology of cata-
lytic materials was obtained by a scanning electron microscope (SEM:
JSM-6301F, JEOL) and a transmission electron microscope (TEM:
JEM-2100, JEOL). BET surface areas, pore volumes, and average
pore diameters of the prepared samples were obtained from N2
(77 K) adsorption measurement using a Micromeritics ASAP2020M
system. Therein, the samples were pretreated under vacuum at
250 °C for 4 h before the measurement. The average pore diameter
data were calculated according to the Barrett–Joyner–Halenda
(BJH) model in absorption and desorption period.
2.4. General procedure for the dehydration of fructose and the product
analysis method
All the dehydration reaction experiments were performed in a
100 mL autoclave equipped with magnetic stirring and a temperature
controller. Herein, a typical step on dehydration of fructose is given in
the following: 1.0 g fructose, 0.1 g catalyst and 10 mL solvent were
added in order after the air in autoclave is replaced with nitrogen for
three times. Then, the autoclave is sealed, and the mixture was stirred
and preheated to 100 °C. Next, the reaction temperature was kept for
100 min. When the reaction was finished, the mixture was transferred
to a volumetric flask. The products were diluted with anhydrous etha-
nol. The yield of HMF was obtained based on the analysis by HPLC
with external standard method.
The quantitative analysis of the products was performed on a
Cometro 6000 equipped with LDI pump and PVW UV detector. Chro-
matographic column type is Kromasil, C18, 5 μ, 250 × 4.6 mm. Qualita-
tive analysis is carried on the Agilent 6890/5973 GC–MS. The NMR
spectra are recorded on an INOVA 500 MHz spectrometer.
In the present study, we propose a new efficient preparation of HMF
from hexoses with mixed SnO2–ZrO2 and SO24−/SnO2–ZrO2 solid acid cata-
lysts. These catalysts are prepared by Sol–gel method using Zr(OC3H7)4 and
dimethyltin dichloride [Sn(CH3)2Cl2] or tin(IV) chloride (SnCl4) as the
metal precursors. The selective and efficient conversion of fructose to pro-
duce HMF is achieved. Moreover, the effects of different Sn-based materials,
reaction temperature and reaction time were investigated in detail.
2. Experimental section
2.1. Reagents
Fructose, glucose, SnCl4, Sn(CH3)2Cl2, deionized water, Zr(OC3H7)4,
ethanol, ammonia, sulfuric acid and silver nitrate are analytic grade
and purchased from commercial sources. Dimethyl sulfoxide (DMSO),
tetrahydrofuran (THF) and acetic ether (CH3COOC2H5) were purified
by distillation prior to use. The HMF as a standard sample in HPLC anal-
ysis is purchased from Alfa Aesar.
2.5. Separation of the product 5-hydroxymethylfurfural (HMF)
After the dehydration of fructose, the mixture was added into a sat-
urated aqueous NaHCO3 solution and stirred with a magnetic stirrer
overnight. The product was extracted four times with CH3COOC2H5.
The organic phase was collected and dried with anhydrous sodium sul-
fate. The organic layer was distilled under reduced pressure to obtain
pure HMF as a main product. 1H NMR spectrum (DMSO-d6): 3.396–
3.438 (d, 1H, J = 7.078), 4.483 (s, 2H), 6.580–6.586 (d, 1H, J = 3.417)
7.466–7.473 (d, 1H, J = 3.417), 9.522 (s, 1H); 13C NMR spectrum
(DMSO-d6): δ 56.524, 56.650, 110.385, 152.413, 162.805, and 178.667.
2.2. The preparation for catalyst
a) The synthesis of SnO2–ZrO2 catalytic materials: a certain amount of
Zr(OC3H7)4 and Sn(CH3)2Cl2 or SnCl4 were added into a 250 mL
round bottomed flask, and then directly dissolved in anhydrous
ethanol assisted by the ultrasonic agitation. In the following,
NH4OH–ethanol (1:1, v/v) solution was added dropwise into the
above solution until the pH = 11. The mixture was stirred and
heated at 83 °C with an oil bath and refluxed for 1.5 h until the
corresponding colloidal were formed completely. In order to remove
the left feedstock , the solid product was filtered and washed by distilled
water, ethanol and ethyl acetate, respectively. Then, the obtained solid
was dried at 100 °C overnight and calcinated at 550 °C for 4 h. Herein,
the different catalysts with Sn/Zr = 0.1, 0.2, 0.03, 0.05 (g/g) from
Zr(OC3H7)4 and Sn(CH3)2Cl2 are signified by DZ-1, DZ-2, DZ-03 and
DZ-05, respectively. The catalyst from Zr(OC3H7)4 and SnCl4 with
Sn/Zr = 0.05 is represented by TZ-05. The uncalcinated catalysts
are signified by n-DZ-05 and n-TZ-05.
3. Results and discussion
3.1. Physical properties of solid catalysts
3.1.1. XRD patterns
Fig. 1 shows the XRD patterns of the different catalytic materials in-
cluding n-DZ-05, DZ-05, SDZ-05, n-TZ-05, TZ-05 and STZ-05 samples. It
is found that the distinct peaks of monoclinic zirconium oxide (m-) and
tetragonal zirconium oxide (t-ZrO2) both appear after being treated
at 500 °C (DZ-05, TZ-05, SDZ-05 and STZ-05), in which the peaks at
2θ = 17.4°, 24.1°, 24.5°, 28.2° and 38.2° are assigned to the diffrac-
tion of (1 0 0), (0 1 1), (1 1 0) (−1 1 1) and (1 1 1) crystal of m-ZrO2,
and the peaks at 2θ = 30.3°, 35.3°, 50.4°, 50.7°, 60.3° and 74.5° are

40
Y. Wang et al. / Catalysis Communications 50 (2014) 38–43
3.1.3. BET measurement
Textural properties of the Sn-based catalysts derived from the
nitrogen physisorption are shown in Table 1. The results indicate
that, compared to the n-DZ-05 and n-TZ-05, the surface area of
SDZ-05 and STZ-05 are increased from 7.8 m2·g−1 to 259.9 m2·g−1
and from 12.6 m2·g−1 to 392.4 m2·g−1, respectively. Moreover, the
whole pore volumes are also increased from 0.0409 to 0.467 cm3·g−1
(n-DZ-05 to SDZ-05) and from 0.107 to 0.663 cm3·g−1 (n-TZ-05 to
STZ-05); otherwise, there is a certain decrease in the average pore
diameter.
3.1.4. SEM images
In order to obtain the structure and morphology of different cata-
lysts, the SEM characterizations are also performed. Fig. 3a–c shows
the SEM images of n-DZ-05, DZ-05, and SDZ-05, and Fig. 3d–e indicates
the SEM images of n-TZ-05, TZ-05 and STZ-05. As a result, it is found that
there exists the loose surface in the prepared hydroxides n-DZ-05 and
n-TZ-05, and the tight surfaces are formed in DZ-05 and TZ-05 which
is the function of calcination at 550 °C. Moreover, the materials become
more regular and smooth in the images of SDZ-05 and STZ-05. This
should be the influence of immersion in H2SO4 solution.
Fig. 1. XRD patterns of different catalytic materials.
attributed to the representative diffractions of t-ZrO2. In addition, it can
be seen that the content of m-ZrO2 is higher in DZ-05 and SDZ-05 mate-
rials, while the content of t-ZrO2 is higher in TZ-05 and STZ-05 material.
Herein, the diffraction peak of SnO2 is very weak which is probably con-
tributed to the existence of nano oxide particles. In addition, there is no
obvious effect on the diffraction peaks after sulfation with H2SO4. It con-
firms that the framework structure of SO24−/SnO2–ZrO2 is always consis-
tent with that of SnO2–ZrO2 material.
3.1.5. TEM images
In the following, the catalytic materials are characterized by TEM
technique. As shown in Fig. 4, the average particles are obtained after
calcination at high temperature (Fig. 4b and e). The size of particles in
sulfated samples is similar with the metal oxides (Fig. 4c and f), but
the linkage between different particles become more popular which
can be attributed to the effect on the aggregation of partial metal
oxide particles in SDZ-05 and STZ-05 materials.
3.1.2. TG–DTG detection
The detection of TG–DTG of n-DZ-05 and SDZ-05 was performed and
the results are shown in Fig. 2. As a result, it is found that there exist three
obvious regions for the weight loss in which the scope of temperature are
respectively 26–90 °C, 190–250 °C and 310–460 °C in the investigation
of n-DZ-05 material. The first and second losses of weight are attributed
to the removal of water absorbed in the surfaces of n-DZ-05. The third
loss of weight is probably due to the dehydration of Sn(OH)x and
Zr(OH)4 to form the oxides. In the TG–DTG graphs of SDZ-05, the loss
of weight appear in the regions of 45–90 °C, 170–225 °C and
550–780 °C, respectively. The first and second losses of weight are con-
tributed to the removal of water absorbed in the surfaces of the cata-
lysts. The third loss of weight is contributed to the removal of SOx and
the breakdown of acid structure. Otherwise, all the peaks showed that
these processes were endothermic for the loss of weight. It should
be motioned that TG–DTG results of n-TZ-05 and STZ-05 are similar
with those of n-DZ-05 and SDZ-05 materials.
3.2. Catalytic activities of various catalysts in the dehydration of fructose
3.2.1. The catalytic performance of different Sn-based heterogeneous
catalysts
In order to investigate the catalytic performance of different Sn-based
catalysts, the dehydration of fructose is chosen as a model and the results
are given in Table 2. First, it is found that the ratio of Sn and Zr has the in-
fluence on the catalytic activity of SnO2–ZrO2 catalyst. The yields of HMF
are 45%, 54%, 51% and 34% when DZ-03, DZ-05, DZ-1 and DZ-2 are
employed as the catalysts, respectively (entries 1–4). Moreover, the orig-
inal n-DZ-05 has also quite a few catalytic activity, and the yield of HMF is
40% in the presence of n-DZ-05 in DMSO (entry 5). Furthermore, the
sulfated SnO2–ZrO2 SDZ-05 showed higher activity for the fructose
dehydration in which the yield of HMF arrives at 75% (entry 6). In the
following, THF and THF–H2O are used as solvents for the dehydration
Fig. 2. The results for TG–DTG detection of n-DZ-05 catalyst (a) and SDZ-05 catalyst (b).

Y. Wang et al. / Catalysis Communications 50 (2014) 38–43
41
Table 1
The textural properties of different Sn-based heterogeneous catalysts.
Catalysts
BET surface area (m2g−1
)
Pore volume (cm3g−1
)
Average pore diameter (nm)
BJH adsorption
BJH desorption
n-DZ-05
n-TZ-05
SDZ-05
STZ-05
7.8
12.6
259.9
392.3
0.0409
0.107
0.467
0.663
7.52
4.74
4.52
4.49
21.8
21.7
14.1
13.2
of fructose. It is found that 53% and 47% yields of HMF are obtained in
THF–H2O and THF when DZ-05 is used as the catalyst (entries 7 and
8). In addition, the yield of HMF is respectively 60% and 34% in the
presence of SDZ-05 and n-DZ-05 in THF–H2O solvent (entries 9 and
10). As comparison, the blank experiment is performed in absence of
any catalyst, and only less than 1% yield of HMF is obtained (entry
11). On the other hand, the TZ-05, n-TZ-05 and STZ-05 are also used
as the catalysts in the dehydration of fructose. As a result, 53%, 51%
and 75% yield of HMF is obtained in DMSO (entries 12–14). This indi-
cates that using SnCl4 as the metal precursor of tin is superior to the
Sn-based solid catalysts. On the other hand, the dehydration of glucose
is investigated in the presence of DZ-05, TZ-05, SDZ-05 and STZ-05, in
which 5%, 6%, 8%, 9% yields of HMF were obtained (entries 15–18). It
shows that the conversion of ketose is superior to the conversion of
aldose to HMF with these Sn-based heterogeneous catalysts.
water in the solution deactivating the active acid sites of SDZ-05 catalyst.
It is also consistent with the SDZ-5 containing the numerous absorbed
H2O molecules, which can be concluded from the TG–DTG result of
SDZ-05 catalyst.
3.2.2. The effect of reaction time
The effect of reaction time has been studied in order to reveal the
character of catalytic reaction in the presence of SO24−/SnO2–ZrO2 cata-
lyst. Fig. 5 shows the results for the dehydration of fructose by SDZ-05
and STZ-05 catalysts during different periods. It is found that the yield
of HMF gradually increases along with the time being increased from
30 min to 150 min. When the time was extended to 180 min or
210 min, the yield of HMF is decreased a little. It can be attributed that
the occurrence of by-products is probably more rapid than the generation
of HMF.
Considering the above characterized physical properties, the catalyt-
ic activity of SDZ-05 is much higher than that of the n-DZ-05 which
should be attributed to elevation of surface area (from 12.6 m2·g−1 to
259.9 m2·g−1) and pore volume (0.107 to 0.467 cm3·g−1) except the
increase of acid sites in SDZ-05 compared to that in the n-DZ-05 catalyst
(see IR spectra in SI). Besides, the more little average pore diameters of
SDZ-05 and STZ-05 compared to those of n-DZ-05 and n-TZ-05 catalysts
probably decrease the generation of polymeric by-products to improve
HMF selectivity. In addition, the catalytic activities of TZ-05 and STZ-05
are higher than those of DZ-05 and SDZ-05, which is also correlated to
the increase of surface area and pore volume of these materials. On
the other hand, in DMSO solvent, the yield of HMF increases from 54%
to 75% when the catalyst DZ-05 is replaced by SDZ-05; in THF–H2O
solvent, the yield of HMF only increases 7% (from 53% to 60%) when
DZ-05 is changed to SDZ-05 catalyst. This is probably due to the excess
3.2.3. The effect of reaction temperature
The effect of temperature on the dehydration of fructose was also
investigated with SDZ-05 and STZ-05 catalysts and the results are
shown in Fig. 6. From these results, it is seen that the yield of HMF in-
creases from 80 °C to 120 °C, and the yield began to decrease when the
temperature was increased to 140 or 160 °C. Therefore, the optimum
temperature is 120 °C in the dehydration reaction. For these SDZ-05
and STZ-05 catalysts, the tendency on the change of product yield kept
in step which is due to their similar physical properties on crystal struc-
ture, average pore diameter and regular surface, etc.
3.2.4. The investigations on the recycle of catalysts
The recycles of DZ-05 and SDZ-05 have been examined in the dehy-
dration of fructose. The investigations are performed at 120 °C for 2.5 h
Fig. 3. The SEM images of different catalytic materials (a. n-DZ-05; b. DZ-05; c. SDZ-05; d. n-TZ-05; e. TZ-05; f. STZ-05).

42
Y. Wang et al. / Catalysis Communications 50 (2014) 38–43
Fig. 4. The TEM images of different catalytic materials (a. n-DZ-05; b. DZ-05; c. SDZ-05; d. n-TZ-05; e. TZ-05; f. STZ-05).
in the presence of 20.0 wt.% catalyst. After the dehydration reaction, the
catalyst was separated, and washed with anhydrous ethanol, and then
dried at 80 °C for 12 h before being reused in the next run. As shown
in Fig. 7, it can be seen that the yield of HMF is almost always about
72% unchanged in five recycle use of SDZ-05 catalyst. These experiment
results show that the SDZ-05 catalyst is efficient and keeps stable in the
dehydration of fructose. Combining the above TEM results, the regular
and smooth surface of the catalyst should be responsible for the stability
in the reaction.
method. The obtained catalytic materials were respectively characterized
by XRD, TG, TEM, SEM and BET techniques. These catalysts have high
thermal stabilities, regular crystal structures and moderate surface area.
Furthermore, the efficient production of HMF from hexose is successfully
performed with SO−4 /SnO2–ZrO2 as the catalyst in DMSO and biphasic
THF–H2O system. The reaction temperature and time are further
optimized. The recycle experiment shows that the SDZ-05 catalyst is
still active after being used five times. So, these Sn-based solid catalysts
are efficient for the conversion of fructose to HMF, which will be very
useful for the biomass utilization in future.
4. Conclusions
In summary, the Sn-based solid acid SnO2–ZrO2 and SO−4 /SnO2–ZrO2
were synthesized by combining the Sol–gel technique and impregnation
Acknowledgment
We are grateful for the financial support of the General Program of the
National Natural Science Foundation of China (project no. 21003093) and
Table 2
Dehydration of fructose with different Sn-based solid catalysts.a
Entry
Substrate
Catalyst
Solvent
Yield of HMF (%)b
1
2
3
4
5
6
7
8
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
D-Fructose
Glucose
DZ-03
DZ-05
DZ-1
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
THF–H2O
THF
THF–H2O
THF–H2O
THF–H2O
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
45
54
51
34
40
75
53
47
60
34
b1
53
51
76
5
DZ-2
n-DZ-05
SDZ-05
DZ-05
DZ-05
SDZ-05
n-DZ-05
none
9
10
11c
12
13
14
15
16
17
18
TZ-05
n-TZ-05
STZ-05
DZ-05
TZ-05
SDZ-05
STZ-05
Glucose
Glucose
Glucose
6
8
9
a
Reaction conditions: 1.0 g substrate, 0.2 g catalyst, in 10 mL solvent, for 2.5 h, at 120 °C.
The results are obtained by HPLC analysis.
The volume ratio of THF and H2O is 3:1.
b
c
Fig. 5. The effect of reaction time with SO24−/SnO2–ZrO2 in the dehydration of fructose
(reaction conditions: 1.0 g substrate, 0.2 g catalyst, in 10 mL DMSO solvent, at 120 °C).

Y. Wang et al. / Catalysis Communications 50 (2014) 38–43
43
Fig. 6. The effect of reaction temperature on the dehydration of fructose (reaction condi-
tions: 1.0 g fructose, 0.2 g catalyst, in 10 mL of DMSO, time 2.5 h).
Fig. 7. The recycle experiment of DZ-05 and SDZ-05 catalysts (reaction conditions: 1.0 g
fructose, 0.2 g catalyst, in 12 mL of DMSO, time 2.5 h).
the Key Program of the National Natural Science Foundation of China
(project no. 21336008).
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Appendix A. Supplementary data
The IR spectra, partial TG–DTG results of catalysts and the GC/MS
spectra, NMR spectra of HMF are contained in the supporting information.
Supplementary data associated with this article can be found, in the on-
line version, at http://dx.doi.org/10.1016/j.catcom.2014.02.023.
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