Conversion of Xylose into Furfural Catalyzed by Bifunctional Acidic Ionic Liquid Immobilized on the Surface of Magnetic Γ-Al2O3

Article abstract of DOI:10.1007/s10562-017-1982-z

Abstract: A novel heterogeneous catalyst was prepared by immobilizing bifunctional acidic ionic liquid of metal Al substituted (BAIL-Al) onto the surface of magnetic γ-Al₂O₃, and characterized by FT-IR, TG, XRD, BET, XPS, VSM, SEM and TEM. The catalytic activity of the prepared solid catalyst was investigated for the conversion of xylose to furfural. On the basis, the effects of temperature, time, amount of catalyst and solvent were studied on the yield of furfural. A furfural yield of 67.5% with 97.3% xylose conversion was obtained from xylose using Fe₃O₄@Al₂O₃-(BAIL-Al) as the catalyst in DMSO at 140 °C for 3?h. The immobilized catalyst has the features of easily separation and recycling as well as good thermal stability. Thus, the immobilized catalyst can be efficiently and easily recycled at least five times without apparent loss of activity in xylose conversion and furfural yield. Graphical Abstract: A novel heterogeneous catalyst was prepared by immobilized bifunctional acidic ionic liquid (BAIL-Al) onto the surface of magnetic γ-Al₂O₃, possessing unique physicochemical properties and excellent catalytic activity for xylose transformation have been developed. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-017-1982-z

Catal Lett
DOI 10.1007/s10562-017-1982-z
Conversion of Xylose into Furfural Catalyzed by Bifunctional
Acidic Ionic Liquid Immobilized on the Surface of Magnetic
γ-Al2O3
Chunyan Wu1 · Wenwen Yuan1 · Yi Huang1 · Yongmei Xia3 · Huamei Yang2 ·
Haijun Wang1 · Xiang Liu1
Received: 6 December 2016 / Accepted: 13 January 2017
© Springer Science+Business Media New York 2017
Abstract A novel heterogeneous catalyst was prepared
by immobilizing bifunctional acidic ionic liquid of metal
Al substituted (BAIL-Al) onto the surface of magnetic
γ-Al2O3, and characterized by FT-IR, TG, XRD, BET,
XPS, VSM, SEM and TEM. The catalytic activity of the
prepared solid catalyst was investigated for the conversion
of xylose to furfural. On the basis, the effects of tempera-
ture, time, amount of catalyst and solvent were studied on
the yield of furfural. A furfural yield of 67.5% with 97.3%
xylose conversion was obtained from xylose using Fe3O4@
Al2O3-(BAIL-Al) as the catalyst in DMSO at 140°C for
3 h. The immobilized catalyst has the features of easily
separation and recycling as well as good thermal stability.
Thus, the immobilized catalyst can be efficiently and easily
recycled at least five times without apparent loss of activity
in xylose conversion and furfural yield.
possessing unique physicochemical properties and excel-
lent catalytic activity for xylose transformation have been
developed.
Graphical Abstract A novel heterogeneous catalyst
was prepared by immobilized bifunctional acidic ionic
liquid (BAIL-Al) onto the surface of magnetic γ-Al2O3,
Keywords Xylose · Bifunctional acidic ionic liquid
(BAIL) · Fe3O4 nanoparticles · Magnetic γ-Al2O3 · Furfural
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-017-1982-z) contains supplementary
material, which is available to authorized users.
1 Introduction
With the increasing consumption of fossil fuels and serious
pollution of the living environment, to research and devel-
opment renewable energy has been one of the top priorities
for scientists. Biomass is a kind of renewable energy with
great prospects. As the main part of biomass, carbohydrate
can be used to prepare into a variety of furan derivatives [1,
2]. Furfural is a typical furan derivative with active chemi-
cal properties, which can be used to prepare high value-
added fine chemicals and liquid fuels [3]. Furfural and its
derivatives not only can be used in alkanes to prepare die-
sel fuel, but also can be used as the basic materials for the
* Huamei Yang
yhmcumt@yeah.net
* Haijun Wang
wanghj329@outlook.com
1
The Key Laboratory of Food Colloids and Biotechnology,
Ministry of Education, School of Chemical and Material
Engineering, Jiangnan University, Wuxi 214122, China
2
School of Chemistry and Chemical Engineering, Xuzhou
University of Technology, Xuzhou 221000, Jiangsu, China
3
State Key Laboratory of Food Science & Technology,
Wuxi 214122, Jiangsu, China
Vol.:(0123456789)
1 3

C. Wu et al.
manufactures of gasoline, diesel and aviation kerosene [4,
5]. For instance, furfural can be converted into furan biofu-
els of 2-methylfuran and 2-methyltetrahydrofuran, wherein
2-methyltetrahydrofuran can be directly used to manu-
facture gasoline as a basic material [6]. There is no doubt
that the demand for furfural in various fields will continue
to increase all over the world due to the growing global
energy crisis [7].
mild conditions [24]. These magnetic nanoparticles have
great stability, and can be easily recovered by an exter-
nal magnet, which is consistent with the concept of green
chemistry.
Efficient production of furfural from xylose could
be achieved by using a one-pot combination of xylose-
to-xylulose isomerization via Lewis acidic sites and
xylulose dehydration via Brønsted acidic sites [19, 25].
Thus, a bifunctional heterogeneous catalyst with Lewis
and Brønsted acidic sites should be a better choice to
convert xylose into furfural. On the surface of catalyst,
Brønsted acid sites (proton donors) can be generated
from highly polarized hydroxyl groups. They can also
form on oxide-based catalysts via proton balance of a net
negative charge introduced by substituting cations with a
lower valence charge. Lewis acid sites are formed from
coordinative unsaturated cationic sites, which leave Mn+
exposed to interact with guest molecules as an acceptor
of an electron pair [26]. Mesoporous γ-Al2O3 is widely
used as a support because of its high specific areas, which
provides a greater contact area and possibly a higher
number of active site for the desired reactions to occur
[27]. At the same time, γ-Al2O3 has Lewis acidic sites
which are benefit to the conversion of xylose [28]. From
our previous work, a bifunctional ionic liquid with high
activity is a better choice for the conversion of biomass
[29].
Many industrial processes of furfural production have
been applied, such as Biofine process, CMIV process,
Suprayield process, and so on [8]. Studies on methods of
better furfural production have never stopped until now.
Morais et al. introduced a novel and green approach to pro-
duce furfural from xylose and biomass hemicellulose in
biphasic system using high-pressure CO2 as an efficient and
sustainable catalyst [9, 10]. Peleteiro et al. reported that fur-
fural was simply and efficiently obtained from eucalyptus
wood and xylose using an acidic ionic liquid as a reaction
medium and a catalyst [11–13]. As green solvents and cata-
lysts, ionic liquids have been received considerable inter-
est in the conversion of biomass because of unique proper-
ties, such as low volatility, high thermal stability, negligible
vapor pressure and so on [14–16]. It was reported that high
yield of furfural from xylose could be gained in ionic liq-
uids [17]. Furfural was a renewable platform chemical with
a bright future and technologies based on ionic liquids were
suitable for furfural production [18]. In addition, Yang
et al. have shown that furfural can be produced effectively
from xylose using AlCl3·6H2O as catalyst and NaCl as co-
catalyst in THF/H2O biphasic system [19]. Zhang et al.
used AlCl3 as catalyst in [BMIM]Cl ionic liquid to produce
furfural from xylose, and 82.8% furfural yield was obtained
at 160°C [20]. It is believed that ionic liquids combined
with aluminum salts have excellent catalytic performance,
however, they also exist serious drawbacks of separation
and recycling. In order to solve these problems, supported
ionic liquids catalysts have been studied, which combine
the advantages of homogeneous and heterogeneous cata-
lysts, with the properties of high catalytic performance,
easy separation, great reusability, etc. [21].
In this work, we synthetized a new catalyst with
bifunctional ionic liquids immobilized on the surface of
magnetic γ-Al2O3, which has strong Lewis and Brønsted
acidic sites. Furthermore, the catalyst exhibits efficient
activity for the dehydration of xylose into furfural.
2 Experimental Section
2.1 Materials
FeCl3·6H2O, FeSO4·7H2O, Al(NO3)3·9H2O, NH4HCO3,
ammonium hydroxide (28 wt%), Cetyltrimethylammo-
nium bromide (CTAB), Imidazole and Sodium ethoxide
were purchased from Sinopharm Chemical Reagent Co.
Ltd. (Shanghai, China). γ-Chloropropyl Triethoxysilane
(CPTES) and 1,3-Propanesultone were purchased from
Aladdin Industrial Inc. (Shanghai, China). Furfural and
xylose were also obtained from Sinopharm Chemical
Reagent Co. Ltd. (Shanghai, China). All solvents and
reagents were purchased from commercial sources and
were used without further purification. Deionized water
was produced with a laboratory water-purification system
(RO DI Digital plus).
Over the past several decades, magnetic solid catalysts
have been widely applied in the conversion of biomass
because of great stability, facile synthesis and easy sep-
aration [22]. An efficient catalyst of magnetic material
grafted with acidic polyionic liquids was designed and
used in the synthesis of promising liquid fuel 5-ethoxy-
methylfurfural (EMF) from HMF and fructose-based car-
bohydrates, showing high catalytic activity and stability
[23]. A magnetic catalyst of Pb/C@Fe3O4 was synthe-
sized by immobilizing Pb on the core-shell structure C@
Fe3O4 magnetic microspheres, which also showed high
activity and extraordinary stability during the oxidation
of HMF into 2,5-furandicarboxylic acid (FDCA) under
1 3

Conversion of Xylose into Furfural Catalyzed by Bifunctional Acidic Ionic Liquid Immobilized…
2.2.4 Synthesis of Fe3O4 Nanoparticles
2.2 Synthesis of the Bifunctional Acidic Ionic Liquid
Supported on Magnetic γ-Al2O3 Material
The Fe3O4 nanoparticles were prepared through a copre-
cipitation method [31]. Firstly, FeCl3·6H2O (6.76 g) and
FeSO4·7H2O (3.8 g) were added to 100 mL of deion-
ized water under vigorous stirring. Secondly, ammonium
hydroxide (28 wt%) was added to the solution until pH 10
was reached. Thirdly, the mixture solution was stirred for
2 h under the condition of 60°C. Finally, the precipitates
were collected with magnet and were washed three times
with deionized water and ethanol successively. After that,
the magnetic NPs were dried in an oven at 40°C for 6 h.
2.2.1 Synthesis of γ‑Al2O3 Nanoparticles
γ-Al2O3 was prepared using sol-gel method. At first,
1 g L−1 CTAB solution was prepared with distilled water.
Then, Al(NO3)3·9H2O and NH4HCO3 were respectively
dissolved in the above solution in order to have the mixture
solution concentration of 27 and 12%. NH4HCO3 solution
was slowly added to Al(NO3)3 solution under vigorously
stirring. NH4HCO3 solution was stopped dropping until
the sol was completely formed which was continued to stir
for 1 h and age for 48 h. The prepared sol was filtered and
dried in vacuum at 60°C for 6 h. Finally, the xerogel pow-
der was calcined at 550°C for 3 h, and γ-Al2O3 nanoparti-
cles were obtained.
2.2.5 Synthesis of the Magnetic Catalyst Material
(Fe3O4@Al2O3‑(BAIL‑Al))
Typically, γ-Al2O3-(BAIL-Al) (100 mg) and Fe3O4 (20 mg)
was added to 20 mL ethanol solution and vigorously stirred
for 12 h. After reaction, the catalyst material was separated
by magnet, which was dried in the oven at 40°C over-
night. The obtained catalyst was denoted as Fe3O4@Al2O3-
(BAIL-Al), and the synthetic route of the magnetic catalyst
was illustrated in Scheme 1.
2.2.2 Synthesis of the Bifunctional Acidic Ionic Liquids
The bifunctional acidic ionic liquids were prepared accord-
ing to the literature method with a modification [30]. Imi-
dazole (3.4 g) and CPTES (12 g) were dissolved in tolu-
ene and refluxed for 24 h at 110°C under N2 atmosphere.
After reaction, 1,3-Propanesultone (6.1 g) was added to the
above mixture solution and stirred for 24 h continuously.
The solvent was evaporated under reduced pressure and
the obtained product was washed three times with diethyl
ether. The obtained compound was dissolved in ethanol
and HCl was slowly added to the solution at 70°C for 2 h.
Then, metal chlorides were added to the above mixture
solution and stirred for another 2 h. The mixture was fil-
tered and evaporated under reduced pressure. The obtained
product was vacuum-dried at 40°C for 12 h. Finally, the
target bifunctional acidic ionic liquids (BAIL-M) were
obtained. The acid ionic liquid (AIL-Cl) and bifunctional
acid ionic liquids (BAIL-Al, BAIL-Cr, BAIL-Sn, BAIL-
Fe) were characterized by FT-IR (see supporting informa-
tion Fig. S1).
2.3 Catalyst Characterization
SEM images were obtained via a HITACHI S-4800 field-
emission scanning electron microscope. Transmission elec-
tron microscopy (TEM) was performed on a JEOL JEM
model 2100 microscope operated at 200 kV. FT-IR meas-
urements were recorded on a Nicolet 360 FT-IR instrument
(KBr discs) in the wavenumber range of 4000–500 cm−1.
Thermogravimetric analysis (TGA) was performed on a
STA409 instrument under a nitrogen atmosphere at a heat-
ing rate of 20°C min−1 from 25 to 700°C. Powder X-ray
diffraction (XRD) patterns were collected by using a Bruker
D8 Advance powder diffractometer (Cu/Kα) in the 2θ range
of 10–80° with a scanning speed of 4°/min at 40 kV and
20 mA. The X-ray photoelectron spectroscopy (XPS) spec-
tra were recorded by Perkin Elmer PHI 5000 ESCT System.
The pore volume, pore size and specific surface area were
measured by N2 adsorption/desorption analysis (Micromer-
itics ASAP 2020) at 77 K using Brunauer–Emmett–Teller
(BET) and Barrett–Joyner–Halenda (BJH) methods. Mag-
netic measurements were carried out using a superconduct-
ing quantum interface device magnetometer (SQUID VSM)
at room temperature in an applied magnetic field sweeping
from −10 kOe to 10 kOe.
2.2.3 Synthesis of the Bifunctional Ionic Liquid Supported
on γ‑Al2O3 Material
Typically, γ-Al2O3 (1 g) and (BAIL-Al) (2 g) were added
to 50 mL mixture solution of dry toluene under stirring.
The suspension was refluxed for 24 h under nitrogen atmos-
phere. After reaction, the resulting mixture was cooled and
filtered under reduced pressure. The obtained material was
washed three times with ethanol and dried in the oven at
40°C overnight. The obtained material was denoted as
γ-Al2O3-(BAIL-Al).
2.4 Catalytic Reactions
Typically, a 25 mL Single-necked flask was charged with
xylose (100 mg), Fe3O4@Al2O3-(BAIL-Al) (40 mg) and
1 3

C. Wu et al.
(a)
(b)
OH
Al2O3
OH
OH
OH
OH
HO
HO
HO
(c)
N
N
H
SO3
Si
(EtO)3
AlClx
Toluene
reflux
O
O
O
O
Ethanol
reflux
N
N
N
H
SO3
Fe3O4
N
Si
O
Al2O3
Fe3O4
SO3H
AlClx
Si
O
AlClx
Scheme 1 a Synthetic route of γ-Al2O3, b Synthetic route of bifunctional acidic ionic liquids (BAIL-M), c Synthetic route of BAIL-Al immobi-
lized on magnetic γ-Al2O3
(
)
DMSO (3 mL). The reaction mixture was performed with
vigorous stirring in an oil bath at 140°C for 3 h. After reac-
tion, the reaction mixture was cooled to room temperature,
and the catalyst was separated via a magnet. The 50 μL sam-
ple was obtained from reaction solution which was diluted
with deionized water and analyzed by high-performance liq-
uid chromatography (HPLC).
moles of furfural
Furfural yield (mol%) =
× 100%
moles of starting xylose
3 Results and Discussion
3.1 Catalyst Characterization
3.1.1 SEM and TEM Analysis
2.5 Analysis
Liquid samples were analyzed by HPLC using an Agilent
1100 equipped with a refractive index detector, and a Shodex
SURGER SP0810 (300×8.0) column at a column tempera-
ture of 70°C for analysis. Ultra-pure water was used as the
eluent phase with a flow rate of 0.7 mL min−1. The amount of
furfural and xylose were determined with an external stand-
ard. The conversion of xylose and the yield of furfural were
evaluated using the following equations:
In order to examine the surface morphology and inter-
nal composition of nanoparticles, SEM and TEM were
conducted. Typical surface SEM images of γ-Al2O3 and
γ-Al2O3-(BAIL-Al) particles are illustrated in Fig. 1a, b,
respectively. It can be observed that the morphology of
γ-Al2O3 has been changed drastically as its surface has
been covered chemically with acidic ionic liquid [32].
The core-shell structure of magnetic catalyst was con-
ducted by TEM characterization as shown in Fig. 1c, d.
The apparent dark area was the nuclear center of Fe3O4,
which was surrounded by a grey layer of the coated
Xylose conversion (mol%)
(
)
moles of remaining xylose
moles of starting xylose
=
1 −
× 100%
1 3

Conversion of Xylose into Furfural Catalyzed by Bifunctional Acidic Ionic Liquid Immobilized…
Fig. 2 FT-IR spectrums of a γ-Al2O3, b γ-Al2O3-(BAIL-Al) and c
Fe3O4@Al2O3-(BAIL-Al)
Fig. 1 SEM images of a γ-Al2O3 and b γ-Al2O3-(BAIL-Al) nanopar-
which were used to investigate the stability of the cata-
lyst. For the catalyst Fe3O4@Al2O3-(BAIL-Al), a small
amount of weight loss of the catalyst in the range of
50–100 °C was due to the removal of physically adsorbed
water on the surface of the mesoporous material. Mean-
while, the minor wrapped water of the porosity of
mesoporous particles was eliminated between 100 and
300 °C. Furthermore, in the range of 300–500 °C, ther-
mal decomposition of the bifunctional acidic ionic liquid
resulted in the fasted weight loss of the catalyst and rapid
decline of TG curve with increasing temperature. It was
demonstrated that the catalyst exhibited good thermal
stability below 300 °C.
ticles, TEM image of the catalyst (c) and (d) Fe3O4@Al2O3-(BAIL-
Al)
material, and the average size of the obtained particles
was 40–50 nm [33].
3.1.2 FT‑IR Spectroscopy
The structure of the Fe3O4@Al2O3-(BAIL-Al) catalyst
was characterized by FT-IR technology, the resulting
image shown in Fig. 2. The typical band at 569 cm−1 was
the characteristic Fe–O vibration of Fe3O4, and the peak
at 638 cm−1 was the Al-O vibration of Al2O3. The FT-IR
spectra displayed the peak at 1045 cm−1, belonging to the
Si–O stretching vibration. The broad peak at 3426 cm−1
was attributed to the stretching vibration of O–H in car-
rier and absorbed water. The peak at 1641 cm−1 was
related to OH bending vibration in the surface of car-
rier [34]. At the same time, two characteristic peaks at
1568 and 1458 cm−1 were the C=C and C=N stretch-
ing vibration of the imidazole ring [29]. In addition, the
2931 cm−1 band was attributed to the stretching vibration
of alkyl chain. The presence of −SO3H group was veri-
fied by S=O stretching vibration appearing at 1139 cm−1
[35]. These results indicated the acidic ionic liquid was
supported on the magnetic γ-Al2O3 successfully.
3.1.3 Thermal Analysis
TGA curves of Fe3O4, γ-Al2O3-(BAIL-Al) and the cata-
lyst Fe3O4@Al2O3-(BAIL-Al) were shown in Fig. 3,
Fig. 3 TGA curves of a Fe3O4, b γ-Al2O3-(BAIL-Al) and the catalyst
and c Fe3O4@Al2O3-(BAIL-Al)
1 3

C. Wu et al.
3.1.4 Wide Angle X‑ray Diffraction Study
The XRD patterns of Fe3O4 and Fe3O4@Al2O3-(BAIL-
Al) were shown in Fig. 4. The pattern of the catalyst
showed the presence of characteristic diffraction peaks
at 2θ = 30.3°, 35.4°, 43.2°, 53.7°, 57.1° and 63.0°.
These peaks were assigned to the (220), (311), (400),
(422), (511) and (440) crystal plane diffraction peaks of
Fe3O4 [36]. The pattern showed the diffraction peaks at
2θ = 37.0°, 46.3° and 66.9° were the characteristic peaks
of γ-Al2O3 [37]. The same peaks of XRD patterns were
observed in both of the Fe3O4 and Fe3O4@Al2O3-(BAIL-
AL), indicating that the nanoparticle was pure Fe3O4 with
a spinel structure and that the wrapped process did not
induce any phase change of Fe3O4 [38]. At the same time,
the XRD patterns of γ-Al2O3 and γ-Al2O3-(BAIL-Al)
were compared (see supporting information Fig. S2).
Fig. 5 XPS spectrum of the Fe3O4@Al2O3-(BAIL-Al) catalyst
3.1.5 X‑ray Photoelectron Spectroscopy (XPS) Analysis
in which a thin γ-Al2O3-[BAIL-Al] layer was observed
[23].
The XPS image of the surface element composition of
Fe3O4@Al2O3-[BAIL-Al] catalyst was shown in Fig. 5.
The peaks with binding energy at 531.8, 399.3, 285.6,
198.7, 168.4, 151.5, 118.2, 100.3 and 73.6 eV were cor-
responded to O1s, N1s, C1s, Cl, S, Si2s, Al2s, Si2p and
Al2p, respectively. These XPS results indicated that
the bifunctional acidic ionic liquid was immobilized on
γ-Al2O3 successfully due to the existence of N, C, S, Cl
and Si in the surface of the catalyst. The XPS results also
showed that there were no iron present on the surface of
the catalyst, indicating that Fe3O4 was encapsulated by a
layer, consistent with the TEM results as shown in Fig. 1,
3.1.6 N2 Sorption Studies
The nitrogen adsorption–desorption isotherms and pore
size distributions of γ-Al2O3 and Al2O3-(BAIL-Al) sam-
ples, as shown in Fig. 6. According to the International
Union of Pure and Applied Chemistry (IUPAC) classi-
fication, both materials have a type-IV-shaped isotherm
and a mesoporous structure (pore diameter between 2
and 50 nm) [39]. The surface area, pore size distribution
and average pore diameter were displayed in Table 1. The
results showed that the surface modification over bifunc-
tional acidic ionic liquid has substantially maintained the
Fig. 4 Wide angle powder XRD patterns of a Fe3O4 and b Fe3O4@
Fig. 6 Nitrogen physisorption isotherms and pore size distribution
for the a γ-Al2O3, b γ-Al2O3-(BAIL-Al)
Al2O3-(BAIL-Al)
1 3

Conversion of Xylose into Furfural Catalyzed by Bifunctional Acidic Ionic Liquid Immobilized…
Table 1 Physical properties of γ-Al2O3 and γ-Al2O3-(BAIL-Al)
The results of VSM showed that the prepared catalyst
still had good magnetic property. Therefore, the catalyst
could be separated magnetically from the mixing system
at the end of the reaction.
Entry Sample type
Surface
area
Pore
Average pore
diameter (nm)
volume
(m2 g−1
)
(cm3 g−1
)
1
2
γ-Al2O3
γ-Al2O3-(BAIL-Al) 94.3
247.0
0.22
0.09
3.54
3.66
3.2 Conversion of Xylose to Furfural by the Acidic
Ionic Liquids
The effects of different metal substituted acidic ionic liq-
uids on the transformation of xylose to furfural were inves-
tigated in DMSO and the results were listed in Table 2. The
acidic ionic liquid (AIL-Cl) had a little catalytic activity for
the dehydration of xylose at 140°C for 1 h, a furfural yield
of 33% was obtained (Table 2, entry 1). Bifunctional acidic
ionic liquids of different metal substituted had better cata-
lytic activity, and the bifunctional acidic ionic liquid of Al
substituted (BAIL-Al) was the best among them. A furfural
yield of 73.5% with 93.7% xylose conversion was achieved
by BAIL-Al (Table 2, entry 5). It is superior to some other
ionic liquids because high furfural yield could be obtained
using BAIL-Al with shorter time [12]. So it is indicated
that BAIL-Al has the best catalytic activity, which is ben-
efit to convert xylose to furfural.
mesoporous structure. A decrease in surface area was
observed for γ-Al2O3 and Al2O3-(BAIL-Al) from 247.0
to 94.3 m2 g−1 and the pore volume decreased from 0.22
to 0.09 cm3 g− 1,but the average pore diameters increased
from 35 to 37 Å, which suggested that bifunctional
acidic ionic liquid may be well confined in the surface of
mesoporous γ-Al2O3. In addition, the pore volume, pore
size and specific surface area of the catalyst Fe3O4@
Al2O3-[BAIL-Al] was exhibited (see supporting informa-
tion Table S1 and Fig S3).
3.1.7 Magnetic Analysis
The magnetization curves of the carrier and catalyst were
measured by a vibrating sample magnetometer (VSM) at
room temperature (298 K), as shown in Fig. 7. Saturation
magnetization of the Fe3O4 was 76.4 emu g−1 and satu-
ration magnetization of the catalyst was 17.5 emu g−1.
The saturation magnetization of the immobilized material
decreased due to the introduction of acidic ionic liquid,
weakening the saturation magnetization. Moreover, the
room temperature magnetization curves of the carrier and
immobilized catalyst exhibited no hysteresis which dem-
onstrated their superparamagnetic characteristics [40].
3.3 Conversion of Xylose to Furfural
by the Immobilized Catalyst
Based on the above researches, the bifunctional acidic ionic
liquid (BAIL) showed the best catalytic activity on the con-
version of xylose to furfural. Therefore, the dehydration
of xylose to furfural was measured using the immobilized
catalyst Fe3O4@Al2O3-(BAIL-Al). Furthermore, influences
of solvent, temperature, time and amount of catalyst were
studied on the conversion of xylose to furfural.
3.3.1 Effect of Solvent
During the reaction process of dehydration of xylose to
furfural using the catalyst Fe3O4@Al2O3-(BAIL-Al), the
solvent effect was very obvious. The result was consistent
Table 2 The catalytic activity of different metal substituted acidic
ionic liquids on the conversion of xylose to furfural
Entry
Catalyst
Xylose conversion
(%)
Furfural
yield (%)
1
2
3
4
5
AIL-Cl
61.3
75.4
83.3
89.5
93.7
33.0
40.3
48.2
63.4
73.5
BAIL-Fe
BAIL-Cr
BAIL-Sn
BAIL-Al
Fig. 7 The magnetization curves of the Fe3O4 (a) and the catalyst
Fe3O4@Al2O3-(BAIL-Al) (b)
Reaction conditions: 100 mg of xylose, 3 mL of DMSO, 20 mg cata-
lyst, T=140°C, t=1 h
1 3

C. Wu et al.
Table 3 The effect of different solvents on the conversion of xylose
important factors. Therefore, we investigated the influ-
ence of temperature and time for conversion of xylose to
furfural, and the results were shown in Fig. 8. The reac-
tion time was 1–5 h at different temperature ranged from
120 to 150 °C. At 120 °C low temperature phase, xylose
degradation rate was relatively slow which caused only
46.9% furfural yield for 5 h in DMSO, because an inter-
mediate product of dehydration was formed at the deg-
radation progress of xylose which did not dehydrate to
furfural in time due to low reaction rate. The yield of
furfural gradually increased with the growth temperature,
and 67.5% furfural yield was obtained at 140 °C for 3 h.
The furfural yield was in a similar range to the reported
for xylose dehydration using high-pressure CO2 as a cata-
lyst [10]. While the yield of furfural declined at 150 °C
high temperature phase, because the probability of colli-
sions between the reaction molecules was enhanced with
the growth temperature, resulting in an increase in the
side reaction rate, thereby generating polymers or dehy-
drated byproducts [45]. Therefore, 140 °C and 3 h were
selected as the best reaction temperature and time for the
dehydration of xylose to furfural.
to furfural
Entry
Solvent
Xylose conversion Furfural
(%)
yield (%)
1
2
3
4
5
6
7
8
DMSO
DMF
DMA
97.3
73.4
70.2
69.3
88.4
90.6
86.5
75.1
67.5
40.2
38.6
37.3
51.9
55.8
16.7
44.5
NMP
Toluene
n-Butanol
Ethanol
DMSO-H2Oa
Reaction conditions: 100 mg of xylose, 3mL of solvent, 40 mg of cat-
alyst, T=140°C, t=3 h
aVolume ratio of H2O/DMSO=1:5
with the research that the furfural yield was changed
obviously while different solvents were incorporated to
the reaction media [13, 41]. Therefore, we inspected the
impact of different solvents on the furfural yield using
the catalyst Fe3O4@Al2O3-(BAIL-Al), such as Dimethyl
sulfoxide (DMSO), N,N-Dimethylformamide (DMF),
N,N-Dimethylacetamide (DMA), 1-Methyl-2-pyrrolidi-
none (NMP), toluene, n-butanol and ethanol, as shown in
Table 3.
3.3.3 Effect of the Amount of Catalyst
From the above table, we could find that the catalyst
Fe3O4@Al2O3-(BAIL-Al) showed the best catalytic activ-
ity when DMSO as the reaction solvent under the same
reaction conditions, it was corresponded to the study of
Li and co-workers [42]. Most of xylose was transformed,
and 67.5% furfural yield was obtained. The result was
consistent with the study that DMSO could improve
selectivity and dehydration rate in formation of furfural
[43]. Obviously, n-butanol, toluene, DMF, DMA and
NMP were relatively less efficient solvents in this reac-
tion, with furfural yield of 55.8%, 51.9%, 40.2%, 38.6%
and 37.3%, respectively. In addition, the lowest catalytic
activity was showed in furfural yield when ethanol as a
solvent, which was consistent with the report of Iglesias
[44]. The catalytic activity of Fe3O4@Al2O3-(BAIL-Al)
was inhibited significantly when water was added to the
reaction. Only 75.1% xylose conversion was obtained at
140 °C for 3 h. Moreover, furfural selectivity was rela-
tively low due to the presence of water which made the
reaction equilibrium toward the direction of xylose. At
the same time, part of furfural was continued to generate
the oxidation or polymerization.
Influence of the amount of catalyst on conversion of
xylose to furfural was investigated at 140 °C for 3 h in
order to optimize the catalytic activity of catalyst Fe3O4@
Al2O3-(BAIL-Al). The effect of varying amounts of cata-
lyst for xylose conversion and furfural yield was shown
in Fig. 9. As it can be seen from the figure, when a small
amount of catalyst (20 mg) was added, the conversion of
3.3.2 Effect of Reaction Temperature and Time
Fig. 8 Influence of reaction temperature and time on the conversion
of xylose to furfural. Reaction conditions: 100 mg of xylose, 3 mL of
DMSO, 40 mg of catalyst
During the reaction progress of preparation of furfural
from xylose, reaction temperature and time were very
1 3

Conversion of Xylose into Furfural Catalyzed by Bifunctional Acidic Ionic Liquid Immobilized…
active sites not only promoted a positive reaction, but
also accelerated the degradation of furfural or polymeri-
zation reaction rate, which led to a decline furfural yield.
The results parallel those reported in the literature for the
reactions of xylose using ionic liquids [46]. In summary,
40 mg was the optimum amount of catalyst. Based on a
large number of references, the plausible reaction mecha-
nism for xylose conversion to furfural was put forward, as
shown in Scheme 2 [47–50].
3.3.4 Reusability of the Catalyst
The catalyst Fe3O4@Al2O3-(BAIL-Al) was reacquired from
the mixture by magnetic separation, washed with ethanol
and dried at 40°C in an oven. The reaction temperature
and time were 140°C and 3 h, respectively. The catalyst
was successfully recycled five times for the conversion of
xylose to furfural with a slight decrease on catalytic activ-
ity, as shown in Fig. 10. The catalyst used for the first time,
67.5% furfural yield was obtained from xylose dehydration.
When the catalyst was used at the second time, the catalytic
activity was lower slightly, and the yield of furfural was
63.2%. While the catalyst was recycled 5 times, 58.7% fur-
fural yield was obtained. After using repeatedly, the yield
of furfural occurred to decrease, because the byproduct of
reaction was adhered to the active sites of the catalyst sur-
face, so that the catalyst could not be sufficiently in contact
with the substrate during the next course of the reaction,
thereby the catalytic result of the reaction was decreased.
Fig. 9 Effect of the amount of catalyst on xylose conversion and fur-
fural yield. Reaction conditions: 100 mg of xylose, 3 mL of DMSO,
T=140°C, t=3 h
xylose and the yield of furfural reached 78.3% and 46.2%
respectively. Further increasing the amount of catalyst,
the catalyst activity has been significantly improved.
When the amount of catalyst was 40 mg, 97.3% xylose
conversion and 67.5% furfural yield were obtained. When
the amount of catalyst was continued to increase, the
active site of the catalytic reaction was also increased.
However, the yield of furfural showed a downward trend
under the same reaction conditions, mainly because more
Scheme 2 Plausible reaction
mechanism for xylose conver-
sion to furfural using Fe3O4@
Al2O3-(BAIL-Al) catalyst
1 3

C. Wu et al.
6. Chheda JN, Románleshkov Y, Dumesic JA (2007) Green Chem
9(4):342–350
7. Dias AS, Lima S, Pillinger M, Valente AA (2006) Carbohydr
Res 341(18):2946–2953
8. Jong WD, Marcotullio G (2010) Int J Chem React Eng
8(1):47–54
9. Morais ARC, Matuchaki MDDJ, Andreaus J, Bogel-Lukasik R
(2016) Green Chem 18(10):2985–2994
10. Morais ARC, Bogellukasik
18(8):2331–2334
R
(2016) Green Chem
11. Peleteiro S, Santos V, Garrote G, Parajó JC (2016) Carbohydr
Polym 146:20–25
12. Peleteiro S, Santos V, Parajó JC (2016) Carbohydr Polym
153:421–428
13. Peleteiro S, Lopes AMDC, Garrote G, Parajó JC, Bogel-Łukasik
R (2015) Ind Eng Chem Res 54:8368–8373
14. Zhang Z, Zhao ZK (2010) Bioresour Technol 101(3):1111–1114
15. Liu B, Zhang Z, Zhao ZK (2013) Chem Eng
215–216(3):517–521
J
16. Xiong Y, Zhang Z, Wang X, Liu B, Lin J (2014) Chem Eng J
235 (1):349–355
Fig. 10 Reusability of the catalyst on the conversion of xylose into
furfural. Reaction conditions: 100 mg of xylose, 40 mg of catalyst,
3 mL of DMSO, T=140°C, t=3 h
17. Matsagar BM, Munshi MK, Kelkar AA, Dhepe PL (2015) Catal
Sci Technol 5(12):5086–5090
18. Peleteiro S, Rivas S, Alonso JL, Santos V, Parajó JC (2016)
Bioresour Technol 202:181–191
19. Yang Y, Hu CW, Abu-Omar MM (2012) ChemSusChem
5(2):405–410
In conclusion, reusability of the catalyst Fe3O4@Al2O3-
(BAIL-Al) was very well.
20. Zhang L, Yu H, Pan W, Dong H, Peng X (2012) Bioresour Tech-
nol 130C(2):110–116
21. Wu Z, Li Z, Wu G, Wang L, Lu S, Wang L, Wan H, Guan G
(2014) Ind Eng Chem Res 53(8):3040–3046
4 Conclusion
22. Liu B, Zhang Z (2016) ACS Catal 6(1):326–338
23. Yin S, Sun J, Liu B, Zhang Z (2015) J Mater Chem A
3(9):4992–4999
A series of bifunctional acidic ionic liquids were tested as
catalysts for the conversion of xylose to furfural in order
to choose the best catalytic activity. The magnetic γ-Al2O3
carrier not only has Lewis acidic site, and also has the
advantages of readily separation and recycling. A novel
heterogeneous catalyst Fe3O4@Al2O3-(BAIL-Al) was syn-
thesized by immobilized bifunctional acidic ionic liquid
onto the surface of magnetic γ-Al2O3, which was demon-
strated to be the most active. A furfural yield of 67.5% with
97.3% xylose conversion was achieved at 140°C for 3 h in
DMSO. The immobilized catalyst has been efficiently and
easily recycled at least five times without apparent loss of
activity in xylose conversion and furfural yield. So it is
indicated that the novel heterogeneous catalyst has great
potential in industry applications due to its green prepara-
tion, high activity and high reusability.
24. Liu B, Ren Y, Zhang Z (2014) Green Chem 17 (3):1610–1617
25. Agirrezabal-Telleria I, García-Sancho C, Maireles-Torres P,
Arias PL (2013) Chin J Catal 34(7):1402–1406
26. Weingarten R, Tompsett GA, Conner WC, Huber GW (2011) J
Catal 279(279):174–182
27. Thyssen VV, Maia TA, Assaf EM (2015) J Braz Chem Soc 26
(1):22–31
28. Jenness GR, Christiansen MA, Caratzoulas S, Vlachos DG,
Gorte RJ (2014) J Phys Chem C 118(24):12899–12907
29. Wang Y, Gu Z, Liu W, Yao Y, Wang H, Xia XF, Li W (2015)
RSC Adv 5(75):60736–60744
30. Safaei S, Mohammadpoorbaltork I, Khosropour AR, Moghadam
M, Tangestaninejad S, Mirkhani V (2013) Catal Sci Technol
3(10):2717–2722
31. Jing H, Wang X, Liu Y, Wang A (2015) Chin J Catal 36
(2):244–251
32. Taghavi M, Ghaemy M, Nasab SMA, Hassanzadeh M (2015) J
Polym Res 22(2):1–12
33. Gu Z, Wang Y, Yao Y, Xia X, Wang H, Li W (2015) Catal Lett
145(12):2046–2054
34. Habibi N, Arandiyan H, Rezaei
6(35):29576–29585
M (2016) RSC Adv
References
35. Zhang Q, Luo J, Wei Y (2011) ChemInform 42(14):2246–2254
36. Zheng J, Dong Y, Wang W, Ma Y, Hu J, Chen X, Chen X (2013)
Nanoscale 5(11):4894–4901
1. Zhou P, Zhang Z (2016) Catal Sci Technol 6(11):3694–3712
2. Liu B, Zhang Z (2016) ChemSusChem 9(16):2015–2036
3. Bozell JJ, Petersen GR (2010) ChemInform 12(28):539–554
4. Corma A, de la Torre O, Renz M, Villandier N (2011) Angew
Chem Int Ed 50(10):2375–2378
37. Yaripour F, Shariatinia Z, Sahebdelfar S, Irandoukht A (2015)
Fuel 139(139):40–50
38. Azgomi N, Mokhtary M (2015) J Mol Catal A 398 (4):58–64
39. Masouleh NSG, Taghizadeh M, Yaripour F (2014) Chem Eng
Technol 37(9):1475–1482
5. Corma A, de la Torre O, Renz M (2011) ChemSusChem
4(11):1574–1577
40. Zhang Q, Su H, Luo J, Wei
14(25):201–208
Y (2012) ChemInform
1 3

Conversion of Xylose into Furfural Catalyzed by Bifunctional Acidic Ionic Liquid Immobilized…
41. Peleteiro S, Lopes AMDC, Garrote G, Bogel-Łukasik R, Parajó
JC (2015) Ind Crops Prod 77:163–166
47. Zhang Z, Du B, Quan ZJ, Da YX, Wang XC (2014) Catal Sci
Technol 4(3):633–638
42. Hu X, Westerhof R, Dong D, Wu L, Li CZ (2014) ACS Sustain
Chem Eng 2(11):2562–2575
48. Choudhary V, Sandler SI, Vlachos DG (2012) ACS Catal
2(9):2022–2028
43. Rong C, Ding X, Zhu Y, Li Y, Wang L, Qu Y, Ma X, Wang Z
(2012) Carbohydr Res 350(350):77–80
49. Choudhary V, Caratzoulas S, Vlachos DG (2012) Carbohydr Res
368C(10):89–95
44. Iglesias J, Melero JA, Morales G, Paniagua M, Hernández B
(2016) ChemCatChem 8(12):2089–2099
50. Danon B, Marcotullio G, Jong WD (2014) ChemInform
45(10):39–54
45. Huang R, Qi W, Su R, He
46(24):1115–1117
Z (2010) ChemInform
46. Lima S, Neves P, Antunes MM, Pillinger M, Ignatyev N, Valente
AA (2009) Appl Catal A 363(1–2):93–99
1 3