Conversion of highly concentrated fructose into 5-hydroxymethylfurfural by acid-base bifunctional HPA nanocatalysts induced by choline chloride

Article abstract of DOI:10.1039/c4ra10121a

A series of acid-base bifunctional heteropolyacids (HPAs) (C₆H₁₅O₂N₂)_3-xH_xPW₁₂O₄₀ (abbreviated as Ly_3-xH_xPW) have been designed using different ratios of HPAs with amino acid lysine in order to control their acid-base properties. The amino acid group facilitated the HPAs forming micellar assemblies in choline chloride-fructose deep eutectic solvents. In the dehydration of fructose to 5-hydroxymethylfurfural (HMF), Ly_3-xH_xPW exhibited different catalytic activities because of their different acid-base properties. Among all the HPA catalysts, Ly₂HPW gave the best results with 93.3% conversion and 92.3% HMF yield within a very short time, i.e. 1 min under the conventional temperature of 110 °C using choline chloride (ChCl) as solvent, and this was almost the best result by far. The highest activity and selectivity of Ly₂HPW came from the synergistic effect between certain acidic and basic capacities, which provides ready accessibility to the nucleophilic (-NH₂) and electrophilic (H) sites. Moreover, this catalyst was tolerant to highly concentrated feedstock (～66.7 wt%) with the additive ChCl. Ly₂HPW performed as a heterogeneous catalyst in the ChCl system and could be recycled by simple washing treatment.

Full text of DOI:10.1039/c4ra10121a

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Aacid-base bifunctional heteropolyacid had been used in conversion of fructose into
5-hydroxymethylfurfural

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Conversion of highly concentrated fructose into 5-hydroxymethylfurfural by acid-base
bifunctional HPA nanocatalysts induced by choline chloride
Qian Zhaoa, Zhong Suna, Shengtian Wanga, Guohui Huangb,*, Xiaohong Wanga,*, Zijiang Jiangc, *
a
Key Lab of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast
Normal University, Changchun 130024, P. R. China. Fax: 0086ꢀ431ꢀ85099759; Tel.:
0086ꢀ431ꢀ88930042; Eꢀmail address: wangxh665@nenu.edu.cn
b
School of Life Science, Northeast Normal University, Changchun 130024, China. Tel.:
0086ꢀ431ꢀ85099607; Eꢀmail address: huanggh699@nenu.edu.cn
c Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P.
R. China. Tel.: 0086ꢀ431ꢀ 85262452; Eꢀmail address: jzj2002@sohu.com
A series of acidꢀbase bifunctional heteropolyacids (HPAs) (C6H15O2N2)3ꢀxHxPW12O40 (abbreviated
as Ly3ꢀxHxPW) had been designed using different ratios of HPAs with amino acid lysine in order to
control their acid/base properties. Meanwhile, the amino acid group facilitated the HPAs forming
micellar assembly in choline chloride/fructose deep eutectic solvents. In the dehydration of
fructose to 5ꢀhydroxymethylfurfural (HMF), Ly3ꢀxHxPW exhibited different catalytic activity
because of their different acid/base properties. Among all HPA catalysts, Ly2HPW gave the best
results with 93.3 % conversion and 92.3 % HMF yield within very short time, i.e. 1 min under
conventional temperature of 110 ºC using choline chloride (ChCl) as solvent, and this was almost
the best result by far. The highest activity and selectivity of Ly2HPW came from the synergistic
effect between certain acidic and basic capacity, which provides readily accessible to the
nucleophilic (ꢀNH2) and electrophilic (H) sites. Moreover, this catalyst was tolerant to high
concentrated feedstock (~ 66.7 wt %) with the additive of ChCl. Ly2HPW performed as a
heterogeneous catalyst in the ChCl system and could be recycled by simple washing treatment.
1. Introduction
Carbohydrates derived from biomass are one of the most abundant renewable resources and
possess a great potential of acting as raw materials for the production of many highꢀvalue
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products.1 In this context, much attention has been paid to the synthesis of
5ꢀhydroxymethylfurfural (5ꢀHMF) which was a chemical platform for the production of various
nonꢀpetroleum valuable chemicals and fuels.2 HMF was mainly produced by acidꢀcatalytic
dehydration of fructose,3 and many acid catalysts, such as mineral or organic acids, zeolites, metal
ions,4ꢀ5 acidic ionic liquids, 6ꢀ9 acidic resins,10 and heteropolyacids ,have been investigated for this
important transformation.11 It is well known that mineral acids possess the advantages of high
reactivity, low cost and suitability for applications in industrial processes.12ꢀ13 However, mineral
acids generally give low yield and selectivity of HMF because of various byproducts like formic
acids, levulinic acids and polymers. At the same time, the harsh reaction conditions are
needed.14ꢀ15 In addition, there may be many side reactions when high concentrated fructose is used
as substrates.16 It is generally recognized that it is very difficult to inhibit side reactions at high
temperature within long reaction time. On the other hand, the using of homogeneous acids often
accompanys with inherent drawbacks in the separation of products and the corrosion of equipment.
Heterogeneous ones are the best candidates for the dehydration of fructose into 5ꢀHMF.17 But
some solid acids exhibit low catalytic performance, and it often costs us a very long time to finish
a reaction .18 Therefore, the development of a green and efficient acid catalyst is still a challenge.
By now, the efficient production of HMF from fructose was often conducted in ionic liquids
systems, which is more expensive and thus hinders the applications in industries.19 König and
coꢀworkers firstly reported the successful conversion using choline chloride (ChCl)ꢀbased deep
eutectic solvent (DES) with fructose.20 A series of acid catalysts such as Amberlystꢀ15, FeCl3,
ZnCl2, CrCl2, CrCl3, pTsOH, Sc(OTf), and Montmorillonite had been used in the above
evaluation ,with the HMF yields as 40, 59, 8, 40, 60, 67, 55, and 49 %, respectively, at 100 ºC and
0.5 h. The using of DES not only decreased the reaction temperature, but also shortened the
reaction time when treating with substrates of high concentrations. This may be of interest for the
development of efficient continuous processes for the conversion of carbohydrates into HMF.
Nevertheless, more catalysts need to be evaluated about their catalytic activity in the ChCl
systems for the purpose of developing efficient (low temperature and short reaction time) and
selective (high yield of HMF) systems. Here, we develop a new synthesis protocol for reaching
the goal of getting HMF with high yield and selectivity within very short time even at low
temperature. To achieve this, we introduce a base site into the Brønsted acidic heterpolyacids
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using amino acids as building blocks (Scheme S1), and investigate the dehydration of fructose
using the baseꢀassisted Brønsted acid as catalysts. The acidꢀbase HPA catalyst which gave the
formula as (C6H15O2N2)2HPW12O40 contains double NH2 groups from amino acids as base
functional groups and a H3PW12O40 fragment as the acid one. This kind of catalyst was firstly
reported21 by us applying in the process of the heterogeneous transesterification and esterification
reactions, and it shows an assistance effect of base on reactions catalyzed by Brønsted acids. As a
continuation of our work, we synthesized
a series of acidꢀbase HPAs catalysts,
(C6H15O2N2)3ꢀxHxPW12O40 (abbreviated as Ly3ꢀxHxPW), using the same strategy and evaluated
their catalytic activity in the production of HMF from fructose in the solvent of choline chloride.
Up to 92% yield of HMF can be obtained in the ChCl/ Ly2HPW system within 1 min. The main
advantages lie in (1) the bifunctional catalytic system with readily accessible to the nucleophilic
sites and electrophilic sites for the selective and efficient conversion from fructose to HMF, (2)
less sideꢀreactions within short reaction time (1 min) accompanying with high efficiency, (3) the
formation of assembly micelle in fructose/ChCl, (4) the tolerance to high loading of fructose (~
66.7 wt % ), and (5) the little leaching of the heterogeneous catalysts.
2. Experimental
2.1. Materials
All solvents and chemicals used were obtained from commercial suppliers. H3PW12O40 was
prepared according to the literature procedure 22
.
IR spectra (4000 ꢀ 500 cmꢀ1) were recorded on a Nicolet Magna 560 IR spectrometer (KBr
discs). XRD patterns of the samples were collected on a Japan Rigaku Dmax 2000 Xꢀray
diffractometer with Cu Kα radiation (λ= 0.154178 nm). TEM micrographs were recorded on a
Hitachi Hꢀ600 transmission electron microscope. 31P MAS (magicꢀangle spinning) and 13C MAS
NMR spectra of the samples were measured with a Bruker AVANCE III 400 WB spectrometer
equipped with a 4 mm standard bore CPMAS probe with the X channel turning to 162 and 100.62
MHz, respectively. Elemental analysis was carried out using a Leeman Plasma Spec (I) ICPꢀES
and a PE 2400 CHN elemental analyzer. The consumption of saccharides was measured by
measuring its concentration in the aqueous phase by Highꢀperformance liquid chromatography
(HPLC) equipped with a refractive index detector (Shimadzu LCꢀ10A, HPXꢀ87H column). And
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the concentration of the HMF in the aqueous phase was determined by HPLC with IONꢀ300H
column using a 2: 8 v/v methanol: water (pH = 2) gradient at the flow rate of 0.7ml/min and the
column temperature of 303K, using a UV detector.
The conductivity experiment was used for confirming the formation of the micelle in aqueous
solutions. The catalysts with different concentrations ranging from 0.1 to 2.0 mM were prepared,
and then the electrical conductivity was measured by a conductivity meter.
The surface acidity was investigated using the titration method. The base strength of the
catalysts was determined by using conductivity titration method.23
2.2. Preparation of catalysts
Lysine (Ly, 4mmol) and H3PW12O40 (HPW) (2mmol) was dissolved in dilute hydrochloric acid
solution (1M, 10mL), respectively. Then the lysine hydrochloric acid solution was added dropwise
into the HPW dilute hydrochloric acid solution with vigorous stirring at the room temperature. The
precipitates were obtained by continuously stirring for 2 h followed by filtering. The white
precipitates were then dried at 303 K for 4 h. The resulting (C6H15O2N2)2HPW12O40 was obtained
with a yield of 52 %. Anal. Calcd. for (C6H15O2N2)2HPW12O40 : W, 69.54; P, 0.98; C, 4.54; N,
1.76; H, 0.97 %. Found: W, 69.77; P, 0.82; C, 4.61; N, 1.65; H, 1.01 %.
Other catalysts were synthesized in the same method by using different molar ratios of lysine to
H3PW12O40. The yields of the (C6H15O2N2)0.5H2.5PW12O40, (C6H15O2N2)H2PW12O40 and
(C6H15O2N2)3PW12O40 were 49, 55, and 51%, respectively. Anal. Calcd. for
(C6H15O2N2)0.5H2.5PW12O40: W, 74.70; P, 1.05; C, 1.22; N, 0.47; H, 0.34 %. Found: W, 75.22; P,
1.15; C, 1.06; N, 0.39; H, 0.42 %. Anal. Calcd. for (C6H15O2N2)H2PW12O40: W, 72.89; P, 1.02; C,
2.38; N, 0.93; H, 0.56 %. Found: W, 74.48; P, 1.19; C, 2.03; N, 0.81; H, 0.66 %. Anal. Calcd. for
(C6H15O2N2)3PW12O40: W, 66.48; P, 0.93; C, 6.51; N, 2.53; H, 1.36 %. Found: W, 66.79; P, 1.22; C,
6.29; N, 2.61; H, 1.24 %.
2.3. Dehydration reaction
In a typical experiment: 0.4 g of fructose and 0.6g of choline chloride was mixed together in a
single neck flask at 110 °C. Then 0.016 mmol of catalyst was added and then the reaction was
started . All reaction times provided in the manuscript were the net reaction times and the heating
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periods of the reactors were not taken into account. At the end of the reaction, the reactor was
cooled to the room temperature. Then the resulting productions were diluted by water for detecting
the conversion of fructose and the yield of the HMF. The mixture was centrifuged to separate the
insoluble catalyst for reuse.
3. Results and discussion
3.1. Characterization of catalysts
The IR spectra of asꢀprepared catalysts (Fig. 1) gave four characteristic peaks at 1083, 978, 900,
and 795cmꢀ1, which can be attributed to υas(P–Oa), υas(W–Od), υas (W–Ob–W), and υas (W–Oc–W),
3ꢀ
respectively, and these bands are coincident with those of its parent PW12O40 (1080, 983, 890,
800 cmꢀ1). It indicated that the original Keggin structure of HPW was retained after the formation
of nanoparticles. Peaks at 1615, 1733 and 1489 cmꢀ1 were due to the stretching bands of NH3 ,
+
–COOH and CꢀN of lysine molecules, indicating the existence of lysine in the assembly spheres.
There were a little shifts of the bands of υas(W–Od), υas (W–Ob–W), and υas (W–Oc–W),
demonstrating that the existence of the strong interactions between the HPAs and lysine. The blue
+
shifts of NH2 from 1710 to 1733 cmꢀ1 proved that the NH2 group of lysine is protonated as NH3 .
Therefore, the lysine cation and HPW anion were combined through electrostatic effects.
Fig. 1
The TEM image of Ly2HPW (Fig. S1) in ChCl/fructose demonstrated that the diameters of the
assembly colloid spheres range from 5 to 10 nm. The Energy Dispersive Xꢀray (EDAX) (Fig. S1)
spectroscopy indicated that these hybrids were composed of PW12O40 and lysine, and the
composition was evidenced by the presence of tungsten, phosphorus, and carbon elements in the
assemblies ,with the molar ratio of C: P: W almost 12:1:12. This result was identified with the
results getting from the elementary analysis.
The critical micelle concentrations (CMC) of Ly0.5H2.5PW, LyH2PW, Ly2HPW, and Ly3PW were
0.50, 0.65, 0.6 and 0.55 mM by break points of two nearly straightꢀline portions of the specific
conductivity versus concentration plot 23 (Fig. S2), which confirmed the formation of micelle in
the aqueous solution.
The lowꢀangle XRD patterns (Fig. S3) gave one Bragg diffraction peak appeared at 1.56, 1.46,
1.22 and 1.04º, corresponding to Ly0.5H2.5PW, LyH2PW, Ly2HPW, and Ly3PW, respectively. The
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lowꢀangle XRD showed that Ly3ꢀxHxPW formed layered superstructures with the layer spacing of
5.66, 6.04, 7.27, and 8.48 nm, respectively.
To investigate the thermal stability of Ly3ꢀxHxPW, TGꢀDTA analyses had been carried out (Fig.
S4). The first decrease at up to 200°C corresponds to the loss of water molecules in the material.
The second weight losses (ca. 2%, 4%, 9% and 13%) correspond to Ly0.5H2.5PW, LyH2PW,
Ly2HPW, and Ly3PW, respectively. The curve change at up to 320 °C is probably due to the
decomposition of lysine group, which is in good coordination with the content of lysine in the
catalyst. An exothermic peak with maxima at around 570°C is due to the structure decomposition
of the Keggin anion, which indicating that the sample decomposed into simple oxides at a
temperature higher than 570°C. The results showed the good thermoꢀstability of Ly3ꢀxHxPW.
As was reported previously, the 31P NMR spectrum of H3PW12O40·6H2O gave one peak at ꢀ15.6
ppm.24 The 31P NMR spectra of Ly0.5H2.5PW, LyH2PW, Ly2HPW, and Ly3PW (Fig. 2) had been
tested to determine the Keggin structure. The 31P NMR spectra of all gave one peak at ꢀ16.161,
ꢀ16.168, ꢀ16.000, and ꢀ16.211 ppm, belonging to Ly0.5H2.5PW, LyH2PW, Ly2HPW, and Ly3PW,
respectively. The above results confirmed that the samples kept Keggin structure after assembling.
The change of chemical shift was attributed to the interactions between HPAs and Ly molecules.
Fig. 2
The Brønsted acidic capacity of the samples was measured by titration with diluted NaOH, and
was expressed by the number of equivalents of H+ in the catalysts. The corresponding values of
Ly0.5H2.5PW, LyH2PW, Ly2HPW, Ly3PW and H3PW12O40 were 4.36 mmol/g, 4.15 mmol/g, 3.60
mmol/g, 0.31mmol/g and 4.75 mmol/g, respectively. Meanwhile, the acidic strength of acidꢀbase
HPAs was H0 ꢀ13.6~ ꢀ12.7. Compared with H3PW12O40 (H0 = ꢀ13.6), the acidic strength of
asꢀprepared HPAs decreased due to the partial exchange of proton with lysine cation. The basic
strength of Ly0.5H2.5PW, LyH2PW, Ly2HPW and Ly3PW was between 7.2 and 9.3, which was
higher than that of lysine (pKa = 10.53). This result indicated that the basic strength of the HPA
catalysts was weaker than that of lysine. The basic capacity of Ly0.5H2.5PW, LyH2PW, Ly2HPW
and Ly3PW was 0.09, 0.13, 0.20, and 0.24 mmol/g, respectively. From the above results, it can be
concluded that Ly3ꢀxHxPW exhibited double acid and base property in one.
3.2. Catalytic activity
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3.2.1. Effect of different catalysts
It is known that dehydration of fructose could be catalyzed by Brønsted acid. In order to
determine the base assistance effect on the conversion reaction, different acidꢀbase HPAs had been
used in the dehydration of fructose (Fig. 3) under the reaction conditions of weight ratio of
fructose/ChCl is 2:3, 110 ºC, 1 min. The conversion followed the order as none (28.0 %) < Lys
(34.1 %) < LyH2PW (79.9 %) ~ Ly3PW (81.0 %) < Ly0.5H2.5PW (82.5 %) < Ly2HPW (93.3 %) ~
H3PW12O40 (94.0 %). The yields of 5ꢀHMF were different when using different catalysts ,ordering
as none (19.0 %) < Lys (24.0 %) < LyH2PW (73.1 %) ~ Ly0.5H2.5PW (73.4 %) < H3PW12O40
(75.1 %) < Ly3PW (79.0 %) < Ly2HPW (92.3 %). The catalyst with certain base and acid property
could promote the dehydration of fructose, and Ly2HPW gave the highest efficiency (92.3 % yield)
with the selectivity of 98.9 %. It is reported that the rateꢀdetermining step of fructose dehydration
is the enolisation of fructose.25 Ly2HPW could provide the concerted activation of fructose at the
CꢀOH bond of the anomeric cation by the proton (electrophile) and at the CꢀH of C1 of the
fructose via hydrogen bonding by N (nuclophile) (Scheme 1) as well. This demonstrated that the
coꢀexistence of hydrogenꢀbond donors (−NH2) and protons in Ly2HPW gave synergic potentials
for the selective and efficient conversion of fructose to HMF. Therefore, high efficiency (low
temperature and short time) and high yield of HMF was obtained catalyzed by double acidꢀbase
HPA Ly2HPW.
Fig. 3
Scheme 1
Compared to pure Brønsted acid catalyst H3PW12O40, Ly2HPW gave higher efficiency and
selectivity. The reason was that strong Brønsted acid could catalyze the further rehydration of
HMF into levulinic acid and fomic acid, thus the yield of HMF catalyzing by H3PW12O40 was
lower. The pKa of lysine is 10.53, so lysine could act as a base in the reaction, so it could not play
any role in the dehydration of fructose. It meant that without any acid center, pure base could not
activate fructose at the CꢀOH bond of the anomeric cation. Therefore, the synergic effect of base
and acid was the main reason for the high efficiency and high yield.
The effect of Choline Chloride in the reaction mixtures had been determined by the comparison
with other deep eutectic mixtures of fructose using imidazole, malonic acid, urea, or guanidine
acetic acid (Table S1). It can be seen that Choline Chloride was the best one among all.
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3.2.2. Effect of different time and different temperature
We studied the dehydration of fructose at 70 ºC ꢀ120 ºC (Fig. 4) in order to determine the effect
of the reaction time and temperature on the formation of HMF. It can be seen that the reaction time
and temperature had a large effect on the dehydration of fructose into HMF. At low temperature
such as 70 ºC, the conversion of fructose and the yield of HMF only reached 78.9 % and 70.2 % in
30 min, respectively. Raising the temperature to 110 ºC, the conversion of 93.3 % and the yield
of 92.3 % were obtained only in 1 min. To the best of our knowledge, this might be the best result
because of the short time under the conventional heating conditions (Table S2). As for the yield of
HMF under different temperatures, it can be seen that below 100 ºC, the yield increased with the
time increasing. Over 100 ºC, the yield of HMF decreased because of the formation of polymers.
That is to say high temperature leads to side reactions such as condensation or polymerization.
Fig. 4
3.2.3. Effect of catalyst dosage
The performance of catalyst was examined through using the degradation of fructose (Fig. 5)
and different amount of catalysts under the reaction conditions as fructose/ChCl weight ratio 2:3,
110 ºC in 1 min. The dehydration of fructose could be enhanced by increasing the dosage of
Ly2HPW. The conversion of fructose and the yield of HMF could reach 64.0 % and 47.1 %,
respectively, using 0.003 mmol catalyst. Increasing the usage of catalyst to 0.016 mmol, the best
results of conversion and selectivity were obtained. Further increasement of the amount of the
catalyst did not enhance the conversion and decreased the selectivity due to the accelerating
decomposition of HMF using high dosage of catalyst.
Fig. 5
3.2.4. Effect of feedstock’s concentration
Under the reaction conditions of 0.4 g of fructose, 0.016 mmol of Ly2HPW , 110 ºC , 1 min,
the influence of the fructose/ChCl weight ratio such as 2:6, 3:6, 4:6, and 5:6 had been evaluated
(Fig. 6). It can be seen that the conversion and the HMF selectivity were affected by different
initial concentrations of fructose. The conversion of fructose and the HMF yield first increased
and then decreased with the increase of fructose weight. In this reaction, the usage of fructose was
kept constant while changing the usage of ChCl. From the experiment (Fig. S5), it can be seen that
large amount of ChCl (2:6 or 3:6) did not help fructose dissolving totally and lead to low
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conversion. For the ratio of 4:6, fructose dissolved totally leading to increasing conversion. For
the weight ratio of 5:6, fructose dissolved well but catalytic sites decreased, which resulting in
lower conversion. The highest yield of HMF was obtained as 92.3 % at the fructose/ChCl ratio of
4:6. The loss of selectivity to fructose/ChCl ratio of 3:6 or less was attributed to the more catalytic
sites compared to that of 4:6, resulting in more byꢀproducts like levulinic acid. Compared to 4:6 of
fructose/ChCl ratio, the 7 % reduction of selectivity for that of 5:6 might be attributed to the
higher fructose concentration leading to higher rates of condensation reactions. This result was in
agreement with literature reports 26.
Fig. 6
3.2.5. Recycling experiments
As mentioned above, the catalyst can be easily separated from the production mixtures. At the
end of the reaction, the catalyst was centrifuged and rinsed with water three times. Then it was
calcinated to dry for 4 h at 60 °C. In Fig. S6, the IR spectrum of reused Ly2HPW exhibited the
four characteristics W–Od, W–Ob–W, W–Oc–W and P–Oa asymmetric stretching vibrational peaks
of heteropolyanions, indicating the stability of catalyst during the reaction and regeneration
procedures. The experiments were repeated six times under the same dehydration procedure and
the conversion and yield to HMF were given in Fig. 7. It showed that there was no considerable
change in the catalytic activity of the catalyst even after six reaction cycles. So it is believable that
our solid acid catalyst is stable and can be reused up to a minimum of six reaction cycles.
Fig. 7
To test for leaching of the Ly2HPW catalyst, the catalyst was filtered after mixturing of Ly2HPW,
fructose and ChCl for 20 min and the mixture was allowed to react for 1 min at the same
temperature of 110 ºC. It can be seen that the conversion of fructose was only 30.6 % similar to
the result without any catalysts (Fig. 3), which demonstrated a little leaching of Ly2HPW into the
mixture and Ly2HPW performed as heterogeneous catalysts in ChCl system. The total amount of
Ly2HPW leaching through six runs of the reaction reached 5.0 % of its starting amount .
4. Conclusion
A series of acidꢀbase catalysts based on HPA H3PW12O40 and amino acid lysine had been
developed. They can possess different acid/base properties through controlling of the ratio of HPA
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to lysine . The dehydration of fructose catalyzed by Ly2HPW catalyst gave almost the best
efficiency in the previous reports (93.3 % conversion and 92.3 % HMF yield) within very short
time, i.e. 1 min at 110 ºC using ChCl as a solvent. The highest activity and selectivity of Ly2HPW
with certain acidic and base capacity came from the bifunctional catalytic system with readily
accessible to nucleophilic (ꢀNH2) and electrophilic (H) sites. Moreover, this catalyst was tolerant
to high concentrated feedstock (up to 66.7 wt %) with the additive of ChCl. Ly2HPW performed as
a heterogeneous catalyst in the ChCl system and could be recycled by simple washing treatment.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 51078066),
the major projects of Jilin Provincial Science and Technology Department (20086035, 20100416,
and 201105001).
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Fig. 1 The IR spectra of Ly3-xHxPW and lysine.

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Fig. 2 Solid-state 31P NMR spectra of Ly3-xHxPW. (a) x = 2.5, (b) x = 2, (c) x = 1, and (d) x = 0.

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Fig. 3 Catalytic conversion of fructose to HMF in different catalysts. Reaction conditions: 0.4g of
fructose, 0.6g of ChCl, 0.016mmol of catalyst, 110 ºC and reaction time 1 min.

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Fig. 4 The activity of Ly2HPW on dehydration of fructose under the reaction conditions as 0.4g of
fructose, 0.6g of ChCl, 0.016mmol of catalyst.

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Fig. 5 The yield and conversion of fructose in different amount of catalyst. Reaction conditions:
fructose/ChCl = 4:6, 110 ºC and reaction time 1 min.

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Fig. 6 The influence of fructose/ChCl weight ratio. Reaction conditions: 0.4 g of fructose, 0.016
mmol of catalyst, 110 ºC and reaction time 1min.

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Fig. 7 The catalyst activity in six reaction cycles. Reaction conditions: 0.4 g of fructose, 0.6 g of
ChCl, 0.016 mmol of catalyst, 110 ºC and reaction time 1 min.

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Scheme 1 Mechanism for the dehydration of fructose to 5-hydroxymethylfurfural in ChCl
catalyzed by acid/base HPA catalyst