Three-phase catalytic system of H2O, ionic liquid, and VOPO 4-SiO2 solid acid for conversion of fructose to 5-hydroxymethylfurfural

Article abstract of DOI:10.1002/cssc.201400119

Efficient transformation of biomass-derived feedstocks to chemicals and fuels remains a daunting challenge in utilizing biomass as alternatives to fossil resources. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam (VPO-MCF), is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural (HMF). HMF is a promising, versatile building block for production of value-added chemicals and transportation fuels. The essence of this three-phase system lies in enabling the isolation of the solid-acid catalyst from the aqueous phase and regulation of its local environment by using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf₂N]). This system significantly inhibits the side reactions of HMF with H₂O and leads to 91 mol % selectivity to HMF at 89 % of fructose conversion. The unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled and locally regulated microenvironment near catalytically active sites by using a hydrophobic ionic liquid Set phases to stun! A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural. This unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled microenvironment.

Full text of DOI:10.1002/cssc.201400119

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DOI: 10.1002/cssc.201400119
Three-Phase Catalytic System of H2O, Ionic Liquid, and
VOPO4–SiO2 Solid Acid for Conversion of Fructose to 5-
Hydroxymethylfurfural
Chengcheng Tian,[a, b] Xiang Zhu,[a, b] Song-Hai Chai,*[b] Zili Wu,[b] Andrew Binder,[c]
Suree Brown,[c] Lin Li,[c, d] Huimin Luo,[e] Yanglong Guo,*[a] and Sheng Dai*[b, c]
Efficient transformation of biomass-derived feedstocks to
chemicals and fuels remains a daunting challenge in utilizing
biomass as alternatives to fossil resources. A three-phase cata-
lytic system, consisting of an aqueous phase, a hydrophobic
ionic-liquid phase, and a solid-acid catalyst phase of nanostruc-
tured vanadium phosphate and mesostructured cellular foam
(VPO–MCF), is developed for efficient conversion of biomass-
derived fructose to 5-hydroxymethylfurfural (HMF). HMF is
a promising, versatile building block for production of value-
added chemicals and transportation fuels. The essence of this
three-phase system lies in enabling the isolation of the solid-
acid catalyst from the aqueous phase and regulation of its
local environment by using a hydrophobic ionic liquid, 1-butyl-
3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]-
[Tf2N]). This system significantly inhibits the side reactions of
HMF with H2O and leads to 91 mol% selectivity to HMF at
89% of fructose conversion. The unique three-phase catalytic
system opens up an alternative avenue for making solid-acid
catalyst systems with controlled and locally regulated microen-
vironment near catalytically active sites by using a hydrophobic
ionic liquid
Introduction
The utilization of abundant, renewable biomass resources for
production of carbon-based fuels and chemicals provides a so-
lution for mitigating the growing shortage of fossil resources
and environmental pollution, and promotes the development
of chemical industry in a sustainable manner. Furan derivatives,
such as 5-hydroxymethylfurfural (HMF), are biomass-derived
platform molecules that have been identified as versatile inter-
mediates for the production of fine chemicals, pharmaceuti-
cals, plastic resins, and transportation fuels. However, they are
not yet produced at an industrial scale due to their high pro-
duction cost.[1] The acid-catalyzed dehydration of hexoses such
as fructose to produce HMF (Scheme 1) has been extensively
studied by using various catalytic systems. The catalytic activity
and selectivity for HMF formation depends strongly on the
choice of catalysts, reaction media (i.e., solvents), and condi-
tions.
[a] C. Tian,+ X. Zhu,+ Dr. Y. Guo
Key Laboratory for Advanced Materials
Research Institute of Industrial Catalysis
East China University of Science and Technology
Shanghai 200237 (China)
E-mail: ylguo@ecust.edu.cn
Two categories of catalysts have been explored for the selec-
tive dehydration of fructose: (a) homogeneous acids such as
mineral acids and soluble metal halides,[2] and (b) heterogene-
ous solid acids such as ion-exchange resins,[3] zeolites,[3a,4] tran-
sition-metal phosphates,[5] acid-functionalized silica and propyl-
ene fibers,[3b,6] and modified tantalum hydroxide.[7]. Although
the homogeneous acids are inexpensive and highly active cat-
alysts for the dehydration reaction at high temperatures, the
large-scale application of this process is complicated due to
the high cost of the catalyst recycling, reactor corrosion, and
neutralization of the waste. From an environmental and eco-
nomic point of view, solid-acid catalysts such as H-form zeo-
lites and transition-metal phosphates are more desirable be-
cause they are less corrosive and easier to separate and recy-
cle.
[b] C. Tian,+ X. Zhu,+ Dr. S.-H. Chai, Dr. Z. Wu, Dr. S. Dai
Chemical Sciences Division, Oak Ridge National Laboratory
Oak Ridge, TN 37831 (USA)
E-mail: chais@ornl.gov
dais@ornl.gov
[c] A. Binder, Dr. S. Brown, Dr. L. Li, Dr. S. Dai
Department of Chemistry
University of Tennessee
Knoxville, TN 37996 (USA)
[d] Dr. L. Li
Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs
Commission & Ministry of Education
College of Chemistry and Materials Science
South-Central University for Nationalities
Wuhan, Hubei 430074 (China)
[e] Dr. H. Luo
Energy and Transportation Science Division
Oak Ridge National Laboratory
Oak Ridge, TN 37831 (USA)
Unfortunately, previously reported heterogeneous acidic cat-
alysts suffer from a low HMF yield in aqueous media, resulting
from rehydration of HMF with H2O to form levulinic acid (LA)
and formic acid, self-polymerization of HMF, and/or cross-poly-
[+] These authors contributed equally to this work.
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201400119.
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tion media. The excessive H2O
could lower the HMF selectivity
by promoting the secondary re-
actions of HMF and decrease the
overall activity by competitive
adsorption with the reactants on
the acid sites. This would require
an additional operation to
remove H2O from the reaction
media, making it less attractive
for the practical application of
hydrophilic ILs.
Scheme 1. Reaction Scheme for conversion of fructose to HMF.
Herein, we report a new effi-
cient
three-phase
catalytic
merization between HMF and fructose to form insoluble poly-
mers and humins (Scheme 1).[1a] To enhance the HMF yield, a bi-
phasic solvent system consisting of water and a water-immisci-
ble organic solvent (e.g., primary and secondary alcohols, ke-
tones, cyclic ethers in the C3ÀC6 range) has been investiga-
ted.[1b] The organic solvent continuously extracts the formed
HMF from the aqueous phase in which the catalytic dehydra-
tion of fructose proceeds. Consequently, the undesired rehy-
dration of HMF is suppressed to a large extent, increasing the
HMF selectivity and yield. Dumesic et al. reported a yield of ap-
proximately 70% of HMF from fructose in a biphasic system
catalyzed by either hydrochloric acid[1b] or heterogeneous
system (Scheme 2), consisting of aqueous and ionic liquid (IL)
phases and solid acid catalyst phase of nanostructured vanadi-
um phosphate and mesostructured cellular foam silica (VPO-
MCF), and we apply the system for the production of HMF
from fructose. The first key feature of this system is the choice
of a hydrophobic ionic liquid, i.e., 1-butyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]), which is
denser than water and thus isolates the top aqueous phase
from the bottom solid-acid catalyst. Fructose dissolved in the
aqueous phase transports continuously into the IL phase
through equilibrium partition and subsequently reacts at the
IL–catalyst interface. The isolation of the aqueous phase from
the solid catalyst significantly enhances the selectivity and
yield of HMF, as compared to a typical biphasic system of or-
ganic solvent and H2O in which the catalyst is well dispersed in
the aqueous phase and the catalytic dehydration of fructose
consequently proceeds at the H2O–catalyst interface. The en-
hanced performance due to the use of the H2O–IL solvent
system is attributed, to a large extent, to the inhibition of sec-
ondary reactions of HMF with H2O. To our knowledge, this is
the first report that a H2O–IL biphasic system can act as an effi-
cient solvent system for the selective dehydration of fructose
to HMF. The second key feature is the development of the
silica-supported alkylsulfonic acids[3b]
.
Ionic liquids (ILs) as neoteric solvents have generated much
interest in recent years because of their unique properties
such as negligible vapor pressure, nonflammability, high ther-
mal and chemical stability, and adjustable solvent power for
organic and inorganic substances.[8] Hydrophilic, water-miscible
ILs containing imidazolium-based cations and halogen anions
are often used in order to facilitate the dissolution of hexoses
and metal halide catalysts.[2c,9] For example, Zhao et al. studied
the catalytic conversion of fructose and glucose into HMF in 1-
ethyl-3-methylimidazolium chloride ([EMIM]Cl) with various
metal chlorides as catalysts. CrCl3
appeared to be the most effi-
cient catalyst, leading to a HMF
yield of 69% from fructose dehy-
dration at 808C after a 3 h reac-
tion.[2c] Zhang et al. found that
the HMF yield was strongly af-
fected by the aggregation of the
cations of the ILs (e.g., the imi-
dazolium cations with an alkyl
group of less than four carbons)
and the hydrogen bonds be-
tween the anions of the ILs (e.g.,
ClÀ anion) and fructose.[9b] How-
ever, the use of hydrophilic ILs
would lead inevitably to the ac-
cumulation of water (either pro-
duced during the dehydration
reaction or introduced along
Scheme 2. Schematic illustration for the synthesis of hybrid VPO–MCF solid acid catalyst and catalytic dehydration
with the reactants) in the reac- of fructose in water–IL–(VPO–MCF) three-phase system.
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VPO–MCF hybrid material as a promising heterogeneous solid-
acid catalyst which can be utilized repeatedly without obvious
activity loss for HMF production in the three-phase catalytic
system. The VPO-MCF hybrid material, possessing nanosized
vanadium phosphate (VPO) crystals coated on the surface of
mesostructured cellular foam silica (MCF), was synthesized by
an in situ growth method that we developed recently for syn-
thesis of nanoscopic lanthanide phosphates and barium sul-
fate.[10] As shown in Scheme 2, vanadium pentoxide (V2O5) was
incorporated into the mesoporous host of MCF through an im-
pregnation method, followed by phosphatation of V2O5 using
an organic amphiphilic n-octadecylphosphonic acid as the
phosphate source. The phosphate head forms a strong interac-
tion with vanadium ions while the alkyl chain caps on the V2O5
surface to prevent the growth and/or sintering of VPO nano-
crystals during subsequent calcination. Highly uniform VPO
nanocrystals formed during the subsequent high-temperature
calcination (5508C in air) along with decomposition and oxida-
tion of the organic phosphonic acid.
The broad signal around À38 ppm could be related to phos-
phorus species bound to silicon atoms of the MCF support
through oxygen bridges (PÀOÀSi).[12] Further characterization
of the synthesized VPO–MCF was performed by Raman and
FTIR spectroscopies. From Figure S1, VPO–MCF shows the
same well-resolved Raman bands as pure VPO. The major band
at 955 cmÀ1 can be attributed to n(as) PÀOÀP in the PO4 unit
3À
of VOPO4 phase, the bands at 992 and 1034 cmÀ1 further indi-
cate the presence of V5+-containing species in large propor-
tion.[13] Figure S2 shows the FTIR spectra of VPO, MCF, and
VPO–MCF. For the VPO sample, the bands between 990 and
940 cmÀ1 correspond to n(V=O) or n(V–OH), and the band at
670 cmÀ1 is assigned to d(V–OH) or d(P-OH).[14] The spectrum
of VPO–MCF sample shows a clear vibration peak at 670 cmÀ1
attributed to d(V–OH) or d(P–OH) of the VOPO4 phase and
a Si–OH band of MCF at around 970 cmÀ1. This indicates the
coexistence of VOPO4 and SiO2 phases, in agreement with the
XRD result shown in Figure 1a.
The textural properties of as-synthesized VPO–MCF were
characterized by nitrogen sorption at À1968C. Figure 2 shows
the adsorption–desorption isotherms and the pore-size distri-
bution of MCF and VPO–MCF. Both MCF and VPO–MCF sam-
ples show type IV isotherms, and the hysteresis loop of the
sorption isotherms suggests “ink-bottle” pores with narrower
windows (bottle necks) and larger spherical cells (bottles).[10]
The VPO–MCF retains the characteristic mesopore structure of
the MCF support, although the pore diameter of VPO–MCF
(window size of ꢀ8 nm and cell size of ꢀ21 nm, Figure 2b)
decreased by approximately 2 nm due to the coating of VPO
on the MCF surface. The results
Results and Discussion
The characteristic structure of as-synthesized VPO–MCF was
analyzed by a variety of techniques including powder X-ray dif-
fraction (XRD), solid-state 31P magic-angle-spinning nuclear
magnetic resonance (31P MAS-NMR), and Raman and Fourier
transform infrared (FTIR) spectroscopies. Figure 1a shows the
XRD patterns of VPO–MCF, VPO, and MCF samples. The broad
XRD peak in the range of 2q=18–368 is attributed to the
indicate that no bulk VPO crys-
tals were formed to block the
pores of MCF, and VPO nano-
crystals were well dispersed on
the surfaces of MCF. The use of
the organic ODPA surfactant as
the phosphate source is the key
to controlling the nanocrystal
size of VPO and ensuring the
conformal growth of VPO on the
wall of MCF. The alkane phos-
phonate can react with vanadi-
Figure 1. (a) Powder XRD patterns of VPO, MCF, and VPO–MCF; (b) solid-state 31P MAS-NMR spectrum of VPO–
MCF.
um species highly dispersed on
the surface of MCF to form vana-
dium phosphonate micelles
amorphous silica. For the VPO–MCF sample, the broad peaks
at 2q=12.1 and 29.08 are indexed to be (001) and (200) planes
of lamellar VOPO4 phase (VOPO4·2H2O),[11] respectively, indicat-
ing the presence of nanocrystalline VPO with an average diam-
eter of 5–7 nm as estimated by the X-ray line broadening
method. The other peaks of VPO phase in the range of 2q=
18–258 are completely covered by the very broad peak of
amorphous silica and thus cannot be observed. The chemical
state of phosphate groups in VPO–MCF was probed by solid-
state 31P MAS-NMR (Figure 1b). The NMR spectrum shows
a peak at about À12 ppm and a shoulder at about À22 ppm,
corresponding to the phosphorus species in PÀOÀV bonds.
through a strong electrostatic interaction, as demonstrated in
the previous study for synthesis of nanoscopic BaSO4-MCF
hybrid materials.[10b]
Microscopic investigation by scanning transmission electron
microscopy (STEM) offers a direct visual evidence for the con-
formal formation of VPO nanocrystals on the MCF support, and
a high-angle annular dark-field detector coupled with STEM
can provide a higher contrast for heavy elements in a low
atomic number matrix as compared to conventional bright-
field images. Figure 3 presents representative STEM images of
VPO–MCF sample under bright and dark fields. The dark-field
image (Figure 3b) shows a uniform distribution of VPO as
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Figure 2. Nitrogen adsorption–desorption isotherms and pore size distributions of MCF and VPO–MCF.
providing general information
about the amount and strength
distribution of acid sites, and
FTIR spectroscopy of pyridine
adsorption, probing the nature
(Brønsted- or Lewis-type) of acid
sites. Figure 4 shows NH3-TPD
profiles of MCF and VPO–MCF in
the temperature range of 100–
5008C. According to the temper-
ature regions of NH3 desorption,
the strength of solid acid sites
are formally classified as weak
Figure 3. STEM images of VPO–MCF under (a) bright and (b) dark fields. VPO nanocrystals are indicated by black
arrows.
(<2508C),
moderate
(250–
4008C), and strong (>4008C).[15]
As expected, the MCF (SiO2) sup-
a bright coating on the silica wall. The wall of VPO–MCF exhib-
its a much higher contrast (indicated by the black arrows in
Figure 3b) which can be attributed to the much heavier
atomic weight of V compared to that of Si. No isolated large
nanoparticles of VPO were observed inside the pores, which
was consistent with XRD analysis (Figure 3a). The above results
suggest that VPO nanocrystals grow in the form of thin layered
nanostructures along the wall of MCF. This is the reason why
the pore size of VPO–MCF is slightly smaller than that of the
MCF support after the formation of the VPO conformal nano-
particle coating. An energy dispersive X-ray (EDX) element
mapping of VPO–MCF (Figure S3) measurement shows uniform
X-ray intensities of V, P, and Si signals throughout the mesopo-
rous particles, revealing the existence of a homogeneous distri-
bution of multiple components. As measured by EDX analysis,
the V-loading of VPO–MCF is ~11.3 wt%, and the atomic ratio
of V to P is close to 1:1. The above structural characterizations
by a couple of combined techniques indicate that VPO–MCF is
composed of uniform vanadium phosphate nanocrystals
coated conformably on the mesoporous MCF support.
port exhibits a negligible peak of NH3 desorption due to its ex-
tremely weak acidity. The NH3-TPD profile of VPO–MCF features
a main desorption peak at 1608C, corresponding to the weak
acid sites, and a shoulder peak between 300–3508C, corre-
sponding to the moderate acid sites. The total acid amount of
VPO–MCF, estimated from the amount of desorbed NH3, is
The acid property of VPO–MCF sample was investigated by
temperature-programmed desorption of ammonia (NH3-TPD),
Figure 4. NH3-TPD profiles of MCF and VPO–MCF.
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phosphate groups (ÀVÀOÀPÀ)
and/or coordinatively unsatura-
ted.[5b,14] The characteristic acidi-
ty of VPO–MCF makes it a prom-
ising heterogeneous acid cata-
lyst for the fructose dehydration
to HMF, given that Brønsted acid
sites have been widely accepted
as catalytically active sites for
the dehydration reaction.[16]
The catalytic performance of
as-synthesized VPO–MCF solid
acid catalyst for fructose dehy-
dration to HMF was explored at
1208C in a specifically designed
three-phase system consisting of
H2O, ionic liquid, and solid acid
Figure 5. (a) FTIR spectra of pyridine adsorbed on MCF and VPO–MCF catalysts after thermal treatment of the pyr-
idine-adsorbed samples at elevated temperatures; (b) variation in the integrated areas of IR bands at 1448 (Lewis
acid sites) and 1548 cmÀ1 (Brønsted acid sites) as a function of the temperature of thermal treatment.
0.65 mmolgÀ1, most of which is contributed by the acid sites
of weak and moderate strength. There is a minor amount of
NH3 desorbed from VPO–MCF above 4008C (Figure 4), implying
the presence of strong acid sites.
catalyst (Scheme 2), in which a water-immiscible phase of imi-
dazolium-based ionic liquid ([BMIM][Tf2N]) lies between the
top aqueous phase and the bottom solid-acid catalyst to fully
isolate them from each other. As demonstrated in Figure 6,
The IR spectra (Figure 5) of pyridine adsorbed on MCF and
VPO–MCF were recorded at room temperature (228C) after
thermal desorption of adsorbed pyridine- at different tempera-
tures (up to 4008C) in a helium flow. Consistent with the NH3-
TPD analysis, the featureless IR spectrum of pyridine adsorp-
tion on MCF indicates the poor acidity of the MCF support.
Two types of adsorbed pyridine species were observed on the
VPO–MCF catalyst: a pyridine protonated on Brønsted acid
sites (the band at 1548 cmÀ1) and a covalently bound species
on Lewis acid sites (the band at 1448 cmÀ1).[14] The individual
amount of Brønsted and Lewis acid sites can be quasi-quanti-
tatively estimated by the integrated area of their correspond-
ing IR bands. As shown in Figure 5b, the band area related to
Brønsted acid sites (1548 cmÀ1) decreases continuously on in-
creasing the treatment temperature of the pyridine-adsorbed
VPO–MCF from 22 to 4008C, due to the desorption of pyridine
adsorbed on the acid sites of weak and moderate strength as
defined in the NH3-TPD measurement (Figure 4). The IR band
at 1548 cmÀ1 is still discernible after the thermal treatment at
4008C, suggesting the presence of strong Brønsted acid sites.
In contrast, the area of the band corresponding to Lewis acid
sites (1448 cmÀ1) was less than 20% the area of the band cor-
responding to Brønsted acid sites when the sample was ther-
mally treated at the same temperature, and completely disap-
peared after the treatment at 3508C. This indicates that the
Brønsted acidity of VPO–MCF is much larger in quantity and
stronger in strength than its Lewis acidity. The above acidity
characterization by of pyridine adsorption by means of NH3-
TPD and IR suggests that the VPO–MCF mesoporous material
is dominated by Brønsted acid sites of weak and moderate
strength along with a small fraction of strong Brønsted and
weak/moderate Lewis acid sites. As observed on other acidic
metal phosphates such as ZrPO4 and NbOPO4, surface hydro-
gen phosphate species (e.g., PÀOH groups) are presumably re-
sponsible for the Brønsted acidity of VPO–MCF, while the Lewis
acidity is related to the vanadium ions that are attached to
Figure 6. Catalytic performance of VPO–MCF for fructose dehydration as
a function of reaction time. Reaction conditions: 0.10 g catalyst, 0.23 g fruc-
tose, 3.5 g H2O/[BMIM][Tf2N] (wt/wt of 1:6 ), 1208C.
both fructose conversion and HMF yield over VPO–MCF in-
crease continuously with the reaction time, while HMF selectiv-
ity increases in the initial 8 h from 67 to 88 mol% and then be-
comes stable. After reaction for 20 h, fructose conversion of
89 mol% was obtained along with HMF selectivity of 91 mol%.
In Table S1, the VPO–MCF catalyst in the H2O–IL system for
fructose dehydration to HMF is compared under similar reac-
tion conditions (80–2008C, 1.9–10 wt% fructose, and 0.2–
3.8 wt% catalysts) with other representative catalytic systems
reported previously. At similar conversion levels (75–100%),
our H2O–IL–(VPO–MCF) three-phase system exhibits the best
HMF selectivity (~90 mol%) among those reported for both
homogeneous (e.g., mineral acids and metal chlorides) and
heterogeneous acid catalysts (e.g., ion-exchange resins, zeo-
lites, acid-functionalized metal oxides, and transition-metal
phosphates) dissolved/dispersed in single-phase (e.g., H2O, hy-
drophilic ILs, and DMSO) and/or biphasic (e.g., MIBK-H2O and
(MIBK/2-BuOH)-H2O) solvents.
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Note that fructose has very poor solubility in the hydropho-
bic IL ([BMIM][Tf2N]), and the undissolved fructose was melted
at the reaction temperature (1208C) and suspended as small
liquid droplets in the IL phase. A large amount of insoluble
humin-like heavy products were produced, darkening the cata-
lyst and reaction media when only pre-dried IL was used (see
Table 1). This was probably caused by reaction of the fructose
liquid droplets over the VPO–MCF catalyst. Those heavy prod-
ucts deposited on the catalyst surface could result in the cata-
lyst deactivation by blocking the active sites, consequently
leading to much lower fructose conversion and HMF yield
compared to the H2O–IL biphasic solvent system as shown in
Table 1. When using H2O–IL (wt/wt of 1:6) system, the reaction
media was visibly clear without any insoluble reactant or reac-
tion products observed. It is interesting that an appreciable
amount of H2O (ꢀ1.1 wt%, measured by Carl Fischer titration
method) was found in the IL phase, which greatly improved
the dissolution of fructose. The initial concentration of fructose
in the IL phase was measured to be 0.045 ggÀ1IL
(0.19 ggÀ1H2O in the aqueous phase) when adding 0.23 g fruc-
tose in 3.5 g H2O–IL solvent (H2O/IL=1:6 wt/wt). We also inves-
tigated H2O-saturated IL as a single-phase solvent for fructose
dehydration under the same reaction conditions, but the reac-
tant could still not be fully dissolved. Therefore, to convert
fructose efficiently to HMF, the solvents of H2O and IL need to
work in a synergistic way that so the aqueous phase is respon-
sible for the dissolution of fructose and subsequent partition-
ing of reactant to the IL phase in which fructose undergoes
a dehydration reaction on the surface of solid acid catalyst.
The isolation of solid acid catalyst from the aqueous phase can
reduce, to a great extent, the negative effect of excessive H2O
on the selectivity and yield to HMF.
Table 1. Catalytic performance of VPO–MCF for fructose dehydration.[a]
À1
À1 [e]
Solvent
X [%][b] S [mol%][c] Y [mol%][d] Rate [mmolh
g
]
cat
HMF LA
H2O-[BMIM][Tf2N] 76
88
13
38
8.9 67
33 10
16 13
1.07
0.16
0.20
H2O
76
33
[BMIM][Tf2N]
[a] Reaction conditions: 0.10 g catalyst, 0.23 g fructose, 3.5 g solvent
(H2O/[BMIM][Tf2N]=1:6 wt/wt), 1208C, and reaction time of 8 h. [b] Fruc-
tose conversion. [c] Product selectivity. [d] HMF yield. [e] Formation rate
of HMF.
For comparison with the H2O–[BMIM][Tf2N] system, VPO–
MCF was tested for the dehydration reaction of fructose in in-
dividual H2O and [BMIM][Tf2N] solvents. As shown in Table 1,
the use of H2O as solvent has little effect on the fructose con-
version, but significantly reduces the HMF selectivity to only
13 mol%. The undesired LA was produced in the H2O solvent
system with a much higher selectivity (33 vs. 8.9 mol%) in
comparison with the H2O–IL system. The HMF yield (67 mol%)
À1
and formation rate (1.07 mmolh
g
À1) in the H2O–IL system
cat
after 8 h reaction are almost seven times of those obtained in
H2O, indicating that isolation of the solid-acid catalyst from the
aqueous phase is the key to achieving high activity for the se-
lective production of HMF from fructose. The catalytic activity
of VPO–MCF in the [BMIM][Tf2N] solvent is approximately 43%
of that in the H2O and H2O–IL systems, along with medium se-
lectivities for HMF (38 mol%) and LA (16 mol%). In addition,
there was a considerable amount of insoluble humin-like
heavy products observed in the reaction media and on the cat-
alyst surface.
Both the VPO–MCF catalyst and [BMIM][Tf2N] (HMF dissolved
in the IL phase was removed by extraction using ethyl aceta-
te[9b]) were recycled for the fructose dehydration reaction at
1208C in order to test the stability of this catalytic system
(Table 2). The HMF yield after 4 h reaction is maintained at ap-
proximately 48% after the catalyst is recycled five times, sug-
gesting an excellent stability of the VPO–MCF catalyst for HMF
production. This indicates that the environmental friendly
H2O–ionic liquid–(VPO–MCF) three-phase catalytic system is
catalytically active and stable. The use of this unique system
could open up a new possibility for efficient HMF production.
Conclusions
A novel three-phase catalytic system, consisting of an aqueous
phase, a hydrophobic ionic-liquid phase, and a solid-acid cata-
lyst phase of nanostructured vanadium phosphate and meso-
structured cellular foam (VPO–MCF) was developed for efficient
conversion of biomass-derived fructose to HMF. The essence of
this three-phase system lies in enabling the isolation and the
solid-acid catalyst from the aqueous phase and the regulation
of its local environment by using a hydrophobic ionic liquid
([BMIM][Tf2N]). This system significantly inhibits the side reac-
tions of HMF with H2O and leading to 91 mol% selectivity to
HMF at 89% of fructose conversion. The VPO–MCF hybrid ma-
terial, prepared by an in situ growth method using an organic
alkane phosphonic acid (n-octadecylphosphonic acid, ODPA) as
the phosphate source, is characterized by Brønsted acidity of
weak and moderate strength endowed by VPO nanocrystals
coated on a high-surface-area mesoporous silica support. The
unique three-phase catalytic system opens up an alternative
avenue for making solid-acid catalyst systems with controlled
and locally regulated microenvironment near catalytically
active sites by using a hydrophobic ionic liquid, and provides
insights for developing efficient heterogeneous catalysts for
the HMF production.
Table 2. Catalytic performance of VPO–MCF catalyst during recycling for
HMF production from fructose.[a]
X [%][b]
S [mol%][c]
Y [mol%][d]
Run 1
Run 2
Run 3
Run 4
Run 5
68
64
66
65
66
74
72
74
74
73
50
46
49
48
48
[a] Reaction conditions: 0.10 g catalyst, 0.23 g fructose, 3.5 g solvent
(H2O/[BMIM][Tf2N]=1:6 wt/wt), 1208C, and reaction time of 4 h. [b] Fruc-
tose conversion. [c] HMF selectivity. [d] HMF yield.
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FULL PAPERS
www.chemsuschem.org
[1] a) R. J. van Putten, J. C. van der Waal, E. de Jong, C. B. Rasrendra, H. J.
Heeres, J. G. de Vries, Chem. Rev. 2013, 113, 1499–1597; b) Y. Romꢁn-
Leshkov, J. N. Chheda, J. A. Dumesic, Science 2006, 312, 1933–1937.
[2] a) G. Yong, Y. Zhang, J. Y. Ying, Angew. Chem. Int. Ed. 2008, 47, 9345–
9348; Angew. Chem. 2008, 120, 9485–9488; b) T. Thananatthanachon,
T. B. Rauchfuss, Angew. Chem. Int. Ed. 2010, 49, 6616–6618; Angew.
Chem. 2010, 122, 6766–6768; c) H. Zhao, J. E. Holladay, H. Brown, Z. C.
Zhang, Science 2007, 316, 1597–1600; d) T. Deng, X. Cui, Y. Qi, Y. Wang,
X. Hou, Y. Zhu, Chem. Commun. 2012, 48, 5494–5496; e) J. N. Chheda, Y.
Roman-Leshkov, J. A. Dumesic, Green Chem. 2007, 9, 342–350.
[3] a) K. Shimizu, R. Uozumi, A. Satsuma, Catal. Commun. 2009, 10, 1849–
1853; b) A. J. Crisci, M. H. Tucker, M.-Y. Lee, S. G. Jang, J. A. Dumesic, S. L.
Scott, ACS Catal. 2011, 1, 719–728.
[4] a) V. V. Ordomsky, J. van der Schaaf, J. C. Schouten, T. A. Nijhuis, J. Catal.
2012, 287, 68–75; b) E. Nikolla, Y. Roman-Leshkov, M. Moliner, M. E.
Davis, ACS Catal. 2011, 1, 408–410.
[5] a) F. Benvenuti, C. Carlini, P. Patrono, A. M. R. Galletti, G. Sbrana, M. A.
Massucci, P. Galli, Appl. Catal. A 2000, 193, 147–153; b) V. V. Ordomsky,
J. van der Schaaf, J. C. Schouten, T. A. Nijhuis, ChemSusChem 2012, 5,
1812–1819.
[6] a) C. Tian, C. Bao, A. Binder, Z. Zhu, B. Hu, Y. Guo, B. Zhao, S. Dai, Chem.
Commun. 2013, 49, 8668–8670; b) C. Tian, Y. Oyola, K. M. Nelson, S.-H.
Chai, X. Zhu, J. C. Bauer, C. J. Janke, S. Brown, Y. Guo, S. Dai, RSC Adv.
2013, 3, 21242–21246.
[7] F. Yang, Q. Liu, M. Yue, X. Bai, Y. Du, Chem. Commun. 2011, 47, 4469–
4471.
[8] a) P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 2000, 39, 3772–3789;
Angew. Chem. 2000, 112, 3926–3945; b) A. Riisagera, R. Fehrmanna, M.
Haumannb, P. Wasserscheid, Top. Catal. 2006, 40, 91–102; c) X. Sun, H.
Luo, S. Dai, Chem. Rev. 2012, 112, 2100–2128.
[9] a) M. E. Zakrzewska, E. Bogel-Łukasik, R. Bogel-Łukasik, Chem. Rev. 2011,
111, 397–417; b) C. Shi, Y. Zhao, J. Xin, J. Wang, X. Lu, X. Zhang, S.
Zhang, Chem. Commun. 2012, 48, 4103–4105.
Experimental Section
The VPO–MCF hybrid materials were prepared by an in situ growth
method.[10] First, mesostructured cellular foam silica (MCF) was syn-
thesized as described by Schmidt-Winkel and co-workers.[17]
NH4VO3 was selected as the vanadium precursor and incorporated
into a MCF framework using a solvent evaporation method. Briefly,
the prepared MCF (0.3 g) was added into deionized water contain-
ing the vanadium precursor (0.07 g). The mixture was stirred at
408C for 3 h, and then the temperature was increased to 808C to
completely evaporate water in the vacuum. The product (V-MCF)
was calcined at 3508C for 3 h. Secondly, the prepared V-MCF
(0.3 g) and a certain amount of n-octadecylphosphonic acid (V/P
molar ratio=1) as the phosphate source were refluxed in 20 mL
ethanol for 16 h. The suspension was washed several times with
ethanol and acetone by centrifugation, and the obtained precipi-
tate was dried overnight at 808C and subsequently calcined in air
at 5508C for 3 h to obtain VPO–MCF. The bulk VPO sample was
prepared for a comparative purpose as described in the litera-
ture.[18] Typically, V2O5 (5.0 g) and H3PO4 (30 mL, 85%) were refluxed
in deionized water (120 mL) for 16 h. A yellow solid was recovered
by centrifugation, washed with distilled water (100 mL) and ace-
tone (100 mL), and dried in air at 808C overnight. Catalytic dehy-
dration of fructose to HMF was conducted at 1208C in a 25 mL
round-bottom flask by using 0.1 g catalyst, 0.23 g fructose, and
3.5 g solvent consisting of deionized H2O and ionic liquid ([BMIM]-
[Tf2N]) (H2O/[BMIM][Tf2N]=1/6 in weight). Detailed procedures for
catalyst characterization and catalytic dehydration of fructose are
provided in the Supporting Information.
[10] a) C. Tian, S.-H. Chai, X. Zhu, Z. Wu, A. Binder, J. C. Bauer, S. Brwon, M.
Chi, G. M. Veith, Y. Guo, S. Dai, J. Mater. Chem. 2012, 22, 25227–25235;
b) C. Tian, S.-H. Chai, D. R. Mullins, X. Zhu, A. Binder, Y. Guo, S. Dai,
Chem. Commun. 2013, 49, 3464–3466.
[11] F. Wang, J. L. Dubois, W. Ueda, J. Catal. 2009, 268, 260–267.
[12] J. Frey, C. Lieder, T. Schçlkopf, T. Schleid, U. Nieken, E. Klemm, M.
Hunger, J. Catal. 2010, 272, 131–139.
[13] a) X.-K. Li, W.-J. Ji, J. Zhao, Z.-B. Zhang, C.-T. Au, J. Catal. 2006, 238, 232–
241; b) F. Ben Abdelouahab, R. Olier, N. Guilhaume, F. Lefebvre, J. C.
Volta, J. Catal. 1992, 134, 151–167.
[14] V. V. Ordomsky, V. L. Sushkevich, J. C. Schouten, J. van der Schaaf, T. A.
Nijhuis, J. Catal. 2013, 300, 37–46.
Acknowledgements
This work was funded from the Division of Chemical Sciences,
Geosciences, and Biosciences, Office of Basic Energy Sciences, US
Department of Energy, under Contract No. De-AC05-00OR22725
with Oak Ridge National Laboratory managed and operated by
UT-Battelle, LLC. The DRIFTS experiment was conducted at the
Center for Nanophase Materials Sciences, which is sponsored at
Oak Ridge National Laboratory by the Scientific User Facilities Di-
vision, Office of Basic Energy Science, US Department of Energy.
CCT and YLG also gratefully acknowledge the National Basic Re-
search Program of China (2010CB732300, 2013CB933201), Pro-
gram for New Century Excellent Talents in University (NCET-09-
0343), the Shu Guang Project (10SG30), and 111 Project (B08021).
[15] E. Dumitriu, V. Hulea, J. Catal. 2003, 218, 249–257.
[16] V. Choudhary, S. H. Mushrif, C. Ho, A. Anderko, V. Nikolakis, N. S. Marin-
kovic, A. I. Frenkel, S. I. Sandler, D. G. Vlachos, J. Am. Chem. Soc. 2013,
135, 3997–4006.
[17] a) P. Schmidt-Winkel, W. W. Lukens, D. Zhao, P. Yang, B. F. Chmelka, G. D.
Stucky, J. Am. Chem. Soc. 1999, 121, 254–255; b) P. Schmidt-Winkel,
W. W. Lukens, P. D. Yang, D. I. Margolese, J. S. Lettow, J. Y. Ying, G. D.
Stucky, Chem. Mater. 2000, 12, 686–696.
[18] G. C. Behera, K. M. Parida, D. P. Das, J. Catal. 2012, 289, 190–198.
Keywords: 5-hydroxymethylfurfural · biomass · fructose · ionic
liquids · solid acid catalysts · vanadium phosphate
Received: January 23, 2014
Published online on && &&, 0000
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FULL PAPERS
C. Tian, X. Zhu, S.-H. Chai,* Z. Wu,
A. Binder, S. Brown, L. Li, H. Luo, Y. Guo,*
S. Dai*
Set phases to stun! A three-phase cata-
lytic system, consisting of an aqueous
phase, a hydrophobic ionic-liquid phase,
and a solid-acid catalyst phase of nano-
structured vanadium phosphate and
mesostructured cellular foam is devel-
oped for efficient conversion of bio-
mass-derived fructose to 5-hydroxyme-
thylfurfural. This unique three-phase
catalytic system opens up an alternative
avenue for making solid-acid catalyst
systems with controlled microenviron-
ment.
&& – &&
Three-Phase Catalytic System of H2O,
Ionic Liquid, and VOPO4–SiO2 Solid
Acid for Conversion of Fructose to 5-
Hydroxymethylfurfural
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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8
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These are not the final page numbers!