Catalytic hydrothermal conversion of carboxymethyl cellulose to value-added chemicals over metal-organic framework MIL-53(Al)

Article abstract of DOI:10.1016/j.carbpol.2014.08.065

Catalytic hydrolysis of biomass over solid catalysts can be one of the most efficient pathways for a future sustainable society dependent on cellulose biomass. In this work metal-organic framework MIL-53(Al) without any functionalization was directly employed as an efficient heterogeneous catalyst for the hydrolysis of carboxymethyl cellulose (CMC) to 5-hydroxymethyl-furaldehyde (5-HMF) in aqueous phase. A 5-HMF molar yield of 40.3% and total reducing sugar (TRS) molar yield of 54.2% were obtained with water as single solvent at 473 K for 4 h. The catalyst could be reused three times without losing activity to a greater extent. With the remarkable advantages such as the use of water as single solvent and MIL-53(Al) as a novel heterogeneous green catalyst, the work provides a new platform for the production of value added chemicals and liquid fuels from biomass.

Full text of DOI:10.1016/j.carbpol.2014.08.065

Carbohydrate Polymers 115 (2015) 146–151
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Catalytic hydrothermal conversion of carboxymethyl cellulose to
value-added chemicals over metal–organic framework MIL-53(Al)
∗
Guoli Zi, Zhiying Yan , Yangxia Wang, Yongjuan Chen, Yunlong Guo, Fagui Yuan,
∗
Wenyu Gao, Yanmei Wang, Jiaqiang Wang
The Universities’ Center for Photocatalytic Treatment of Pollutants in Yunnan Province, School of Chemical Sciences & Technology, Yunnan University,
Cuihu North Road No. 2, Kunming 650091, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 April 2014
Received in revised form 9 July 2014
Accepted 13 August 2014
Available online 2 September 2014
Catalytic hydrolysis of biomass over solid catalysts can be one of the most efficient pathways for a future
sustainable society dependent on cellulose biomass. In this work metal–organic framework MIL-53(Al)
without any functionalization was directly employed as an efficient heterogeneous catalyst for the hydrol-
ysis of carboxymethyl cellulose (CMC) to 5-hydroxymethyl-furaldehyde (5-HMF) in aqueous phase. A
5
-HMF molar yield of 40.3% and total reducing sugar (TRS) molar yield of 54.2% were obtained with
water as single solvent at 473 K for 4 h. The catalyst could be reused three times without losing activity
to a greater extent. With the remarkable advantages such as the use of water as single solvent and MIL-
Keywords:
Metal–organic framework
MIL-53(Al)
Biomass conversion
Carboxymethyl cellulose
5
3(Al) as a novel heterogeneous green catalyst, the work provides a new platform for the production of
value added chemicals and liquid fuels from biomass.
© 2014 Elsevier Ltd. All rights reserved.
5
-Hydroxymethyl-furaldehyde
1
. Introduction
(Guo et al., 2013). In order to minimize those negative environmen-
tal impacts, new green approaches have been developed, such as
the use of cellulose enzymes (Percival Zhang, Himmel, & Mielenz,
2006), microwave irradiation (De, Dutta, & Saha, 2011), and solid
catalysts. Indeed, various solid acid catalysts including heteropoly-
acids (Ogasawara, Itagaki, Yamaguchi, & Mizuno, 2011), layered
transition-metal oxides (Tagusagawa et al., 2010), and sulfonated
hierarchical H-USY zeolite (Zhou et al., 2013), have been proposed.
Despite these pioneering studies, it is likely that the main obstacle
to using these conventional heterogeneous mesoporous and micro-
porous catalysts for “bulky” biomass is the limited accessibility of
the reactive sites, which results in inefficient biomass conversion
(Kuo, Suzuki, Yamauchi, & Wu, 2013).
Moreover, some researchers described the use of a mixed-
solvent or ionic liquids for the hydrolysis of biomass (Liu, Xiao,
Xia, & Ma, 2013; Moreau, Durand, Pourcheron, & Razigade, 1994;
Qi, Watanabe, Aida, & Smith, 2008b). However, ionic liquids have
high viscosities and their high cost may limit some applications. So
far reports of hydrolysis cellulose to produce 5-HMF using water
as the only solvent have been very limited in the literature as
we know. Furthermore, the yield of reducing sugar (glucose) for
cellulose conversion was in the range of 40.5–74.5% in most of
systems and few studies concerned about the formation of 5-HMF
by using water as the only solvent (Guo et al., 2013; Tian et al.,
2010). For example, the yield of total reducing sugar (TRS) 54% was
reported, while only 1.6% 5-HMF was obtained over H3PW12O40
Efficient conversion of renewable biomass to useful chemi-
cals and biofuels is one of the most popular topics in green
and sustainable chemistry (Guo, Lian, Yan, Qi, & Smith, 2013).
Hydrothermal treatment is quite promising in this process because
water under high temperature and high pressure behaves as a
reaction medium having outstanding properties (Takeuchi, Jin,
Tohji, & Enomoto, 2007). In general, carboxymethyl cellulose
(
CMC) is a water-soluble derivative of cellulose which is quite
economic and promising as raw materials in the conversion of
biomass. (Paljevac, Primo zˇ i cˇ , Habulin, Novak, & Knez, 2007). And
as a versatile intermediate between biomass-based carbohydrate
chemistry and petroleum-based industrial organic chemistry, 5-
hydroxymethylfurfural (5-HMF) can be used to synthesize a broad
range of chemicals currently derived from petroleum. Therefore,
conversion of biomass to 5-HMF has been extensively studied.
Most of the previouslyreportedstudies have employedcarbohy-
drates such as fructose, glucose, sucrose, inulin and even cellulose,
as feedstock for the synthesis of 5-HMF (Deng et al., 2012). Com-
mon inorganic acids such as HCl, H SO have been used as catalysts
2
4
for the dehydration of biomass but suffers a number of drawbacks.
∗ Corresponding authors. Tel.: +86 871 65031567; fax: +86 871 65031567.
E-mail addresses: zhyyan@ynu.edu.cn (Z. Yan), jqwang@ynu.edu.cn (J. Wang).
http://dx.doi.org/10.1016/j.carbpol.2014.08.065
0
144-8617/© 2014 Elsevier Ltd. All rights reserved.

G. Zi et al. / Carbohydrate Polymers 115 (2015) 146–151
147
catalyst (Tian et al., 2010). Although considerable efforts have been
made, it is still a major challenge to have a heterogeneous catalyst
with high yield of 5-HMF by direct conversion of cellulose in water.
Metal–organic frameworks (MOFs) possess several advantages
such as high surface areas, well-defined structures, the ease of
processability, and structural diversity, which make them very
attractive for catalysis (Li, Eddaoudi, O’Keeffe, & Yaghi, 1999; Phan,
Nguyen, Luu, & Nguyen, 2012). Recently, phosphotungstic acid
were measured by the nitrogen adsorption/desorption measure-
ments using a Beishide 3H-2000PM2 Surface area and porosity
analyzer. Scanning electron microscopy (SEM) images were taken
on a FEI Quanta200 FEG microscope at an accelerating voltage of
15 kV with the pressure in the sample chamber of 1 Torr. High-
resolution transmission electron microscopy (HRTEM) imagines
were taken on a TEM (JEM-2100). To investigate the acidic prop-
erties of the samples, NH3 Temperature-Programmed Desorption
(
PTA) encapsulated in MIL-101(Cr) was used as a solid acid cat-
(NH -TPD) was carried out using a chemisorption analyzer system
3
alyst for dehydration of carbohydrates to 5-HMF in ionic liquids
or DMSO, an HMF yield of 63% was obtained in DMSO (Zhang,
Degirmenci, Li, & Hensen, 2011). However, a major effort has been
required to functionalize these porous frameworks with specific
sites or acid groups for carrying out the catalytic reactions. And
catalytic studies on MOFs without any functionalization as solid
acid catalysts for conversion of CMC to 5-HMF in single aqueous
solvent system has not been reported so far as we know.
MIL-53(Al) with 1D lozenge-shaped tunnels built up from chains
of octahedra sharing OH vertices is appropriate for a Brønsted-
type acid catalyst (Farrusseng, Aguado, & Pinel, 2009; Ferey, 2008).
And many researchers also reported that acid catalysts are helpful
for accelerating the production of HMF under hydrothermal con-
dition (Kuo et al., 2013; Takeuchi et al., 2007). Therefore, these
properties have inspired potential applications of MIL-53(Al) in
catalysis for hydrolysis of biomass. Moreover, water can still be
considered as a preferred solvent for biomass conversion since the
actual biomass can contain a substantial amount of water, and its
properties are tunable with the variation of its temperature and
pressure (Qi, Watanabe, Aida, & Smith, 2008a). Herein, MIL-53(Al)
without any functionalization was employed as an acid catalyst
for the hydrothermal conversion of CMC to 5-HMF using water as
single solvent for the first time.
(ChemBET 3000).
2.3. Carboxymethyl cellulose hydrolysis
A typical catalytic reaction procedure was as follows: 100 mg
of CMC and 75 mg catalyst were dispersed into 80 mL of water
under stirring. Then the solution was transferred and sealed in a
Teflon-lined steel autoclave and heated to a given reaction tem-
perature at autogenous pressure. After cooling the autoclave in
an ice-water bath to room temperature, the reaction mixture was
filtered through a Millipore filter (pore size, 0.45 ␮m) and ana-
lyzed by UV–vis spectrometer (Shimadzu UV-2401PC photometer)
over 200–400 nm. The determined wavelength is 282 nm (Fig. S4),
which is the maximum absorption wavelength of 5-HMF detected
by UV–vis spectrometer. The concentration of 5-HMF was calcu-
lated based on a standard curve obtained with 5-HMF. In addition to
Ultra-performance liquid chromatography analysis (UPLC, Waters)
1
(Fig. S3), the structure of final product was also analyzed by H NMR
spectroscopy (Bruker Avance 300 spectrometer, 300 MHz, CDCl3) in
order to confirm it is HMF. 1H NMR peaks at d (ppm): 4.660 (s, 2H),
6.447–6.459 (d, J = 3.6 Hz, 1H), 7.140–7.152 (d, J = 3.6 Hz, 1H), 9.546
(s, 1H).
The total reducing sugar (TRS) content was determined using the
3
,5-dinitrosalicylic acid (DNS) method. A mixture contained 1 mL
of 3,5-dinitrosalicylic acid (DNS) regent, 3 mL of reaction sample,
2
. Experimental
and 3 mL of H O, was heated for 15 min in a boiling water bath,
2
then cooled to room temperature, and mixed with 5 mL of deion-
ized water. The color intensity of the mixture was measured in a
UV-2401 Model spectrophotometer. The concentration of TRS was
calculated based on a standard curve obtained with glucose.
2
.1. Synthesis of MIL-53(Al)
MIL-53(Al) was synthesized via
a
hydrothermal method
according to Loiseau et al.’s (2004) previous report. 1,4-
benzenedicarboxylic acid (H BDC, 2.88 g) Al(NO ) ·9H O (13.0 g),
2
3
3
2
2.4. Fast hot catalyst filtration experiments
and deionized water (50 mL) were added into a 100 mL Teflon-
lined steel autoclave and heated at 473 K for 72 h. The product
was filtered and washed with water to ensure the removal of
nitric acid formed during the synthesis. The powder obtained was
dried overnight at 353 K in air. The as-synthesized dry powder
was denoted as MIL-53(Al)as. As-synthesized MIL-53(Al)as was acti-
vated according to the previous literature procedure (Rallapalli
et al., 2009). The product was filtered and washed with N,N-
dimethylformamide (DMF) to remove the unreacted BDC, and dried
under vacuum for 2 h. Further it was treated with methanol in order
to replace the DMF molecules trapped inside the cavities of the
product. Finally, it was filtered, washed with methanol, and dried
in an air oven at 353 K for 2 h (Rallapalli et al., 2009). Then, the
sample was further activated at 423 K under vacuum overnight to
ensure complete removal of solvent molecules. The obtained prod-
uct was calcined in conventional manner at 603 K for 72 h and the
calcined product was denoted as MIL-53(Al).
1
00 mg of CMC and 75 mg catalyst were dispersed into 80 mL
of water and loaded into a stainless steel autoclave with a 100 mL
Teflon container. Then, the autoclave and its contents were heated
to 473 K at autogenous pressure for 30 min, then quickly filtrated
the catalyst. The filtrates obtained from the fast hot catalyst fil-
tration was detected by ICP-AES analyzer (Shimadzu SEQUE-NTIAL
PLASMA SPETROMETER ICPS-1000II).
3
. Results and discussion
3
.1. The characterization of catalyst
The diffraction patterns of MIL-53(Al)as and MIL-53(Al) sam-
ples clearly indicates that the materials are well crystalline, and the
obtained peaks of MIL-53(Al)as and MIL-53(Al) are in good agree-
ment with the literature patterns reported earlier by Ferey et al.
(Fig. 1) (Loiseau et al., 2004). The diffraction patterns are obviously
2.2. Characterizations
different, since the guest removal by heating leads to an expansion
of the cell for MIL-53(Al).
Wide angle X-ray powder diffraction (XRD) experiments were
The FT-IR spectra of MIL-53(Al)as and MIL-53(Al) (Fig. 2) exhibit
−
1
conducted on a Rigaku TTRAX III spectrometer with Cu K␣ radia-
vibration bands in the region 1400–1700 cm for the carboxylic
functional groups (Loiseau et al., 2004). The FT-IR of MIL-53(Al)as
◦
◦
tion from 5 to 40 . The Fourier transform infrared spectra (FI-IR)
measurements were performed on a Thermo Nicolet 8700 instru-
ment. Pore size distributions, BET surface areas and pore volumes
−
1
−1
samples exhibits bands at 1601 cm and 1512 cm corresponds
−
1
to COO asymmetric stretching whereas the bands at 1413 cm

1
48
G. Zi et al. / Carbohydrate Polymers 115 (2015) 146–151
MIL-53(Al)
MIL-53(Al)as
5
10
15
20
25
30
35
40
300
400
500
600
700
2
Theta / degrees
Temperature / K
Fig. 1. XRD patterns of as-synthesized, MIL-53(Al)as; purified, MIL-53(Al).
Fig. 3. NH3-TPD patterns of MIL-53(Al).
attribute to COO symmetric stretching (Loiseau et al., 2004). An
of relatively weak acidic sites which was probably Brønsted acid
−
1
additional absorption peak is observed at 1699 cm , which can
be attributed to COOH group of unreacted free BDC acid that
trapped in the cavities of MIL-53(Al)as also seen by XRD data. But
−
1
sites. MIL-53(Al) exhibited acidic amounts of 0.38 mmol g
and
suggested its potential applications in acid catalysis for hydrolysis
of biomass.
−
1
for MIL-53(Al), any absorption bands are not observed at 1699 cm
indicating removal of free BDC molecules after calcination.
3.2. Catalytic performance
From the typical type
I nitrogen adsorption–desorption
isotherm (see the Supporting information Fig. S1), the BET surface
2
−1
MIL-53(Al) catalyst was then tested for hydrothermal conver-
area have been measured to be 1233.4 m g (Langmuir surface
2
−1
sion of CMC. The reaction conditions, such as catalyst dosage,
reaction time and temperature were optimized in advance. Influ-
ence of catalyst dosage on the activity was investigated by varying
area: 1335.3 m g ) with a corresponding micropore volume of
0
3
−1
.45 cm g . The SEM and TEM images reveal that MIL-53(Al) is
composed of rods with a size of about 5 ␮m assembled by the
lozenge shaped crystals (Fig. S2). The definite crystal shape is not
observed and the size distribution is relatively wide, most probably
due to the polycrystalline agglomerate nature of the crystals.
MIL-53(Al) built up from 1D lozenge-shaped tunnels created
by chains of octahedrae sharing OH vertices that are linked
in the two other directions may exhibt acidic property. The
acidic property of MIL-53(Al) was determined by means of NH3
the amount of catalyst in the range of 25–150 mg in 80 mL of H O
2
solution under the same condition. As shown in Fig. 4, an initial
steep increase in the yield of 5-HMF was observed when the amount
of the catalyst was increased up to 75 mg. Beyond this amount, the
yield of 5-HMF slightly decreased. It is probable that large catalyst
dosages provide excess active sites in the system that accelerate
side reactions (including rehydration or condensation, etc.) (Tian,
temperature-programmed desorption (NH -TPD) as shown in
3
Fig. 3. Low temperature peak at ca. 404 K, indicated the presence
18
15
12
MIL-53(Al)as
9
6
3
0
MIL-53(Al)
25
50
75
100
150
Catalyst amount (mg)
4
000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm)
Fig. 4. Effect of catalyst dosage on the CMC hydrolysis by MIL-53(Al) catalyst.
Note: Reaction condition: substrate, 100 mg CMC; reaction time, 11 h; reaction
temperature, 423 K; solvent, H2O 80 mL.)
(
Fig. 2. FT-IR spectra of as-synthesized, MIL-53(Al)as; purified, MIL-53(Al).

G. Zi et al. / Carbohydrate Polymers 115 (2015) 146–151
149
curves were depicted beforehand. Generally, the hydrolysis of cel-
lulose occurs by two consecutive reactions: conversion of cellulose
into reducing sugars (glucose) and the further decomposition of the
formed sugars into other products such as 5-HMF, levulinic acid,
furfural and so on (dos Santos et al., 2013). The yield of TRS was
determined by the equilibrium between CMC hydrolysis and glu-
cose decomposition. Obviously, all the used MOFs have the ability
to convert CMC to sugars and 5-HMF with certain yields except Zn-
MOFs. This did remind us the potential applications of MOFs in the
cellulosic conversion. It is also apparent that MIL-53(Al) exhibits
highest yield of 5-HMF and TRS among the used catalysts in this
work and it is even superior to those systems relevant to the for-
mation of TRS and 5-HMF in the literatures using water as solvents.
Since it is believed that acid catalysts are helpful for accelerating
the hydrolysis of cellulose (Kuo et al., 2013), the well-isolated acid
4
3
2
1
0
0
0
0
0
4
23 K
43 K
63 K
73 K
4
4
4
sites of MIL-53(Al) catalyst observed by NH -TPD can facilitate
3
converting CMC directly to 5-HMF. And the presence of this COOH
groups in MIL-53(Al) materials also promote the adsorption of
CMC and water molecules through hydrogen bonding, resulting in
efficient hydrolysis of CMC (Guo et al., 2013; Suganuma et al., 2008).
Since aluminum was the active component, further compari-
son was made between MIL-53(Al) and other Al doped mesoporous
0
2
4
6
8
10 12 14 16 18 20 22 24
Time / h
Fig. 5. Effect of reaction temperature and reaction time on the CMC hydrolysis by
MIL-53(Al) catalyst.
Note: Reaction condition: substrate, 100 mg CMC; catalyst, 75 mg; solvent, H2O
0 mL.)
(
8
materials such as, dodecylamine templated titania (Al–TiO /DDA)
2
(Yao, Fang, Ou, Wang, & Yan, 2006), rubber latex bio-templated
Tong, Cheng, & Xue, 2013). Therefore, 75 mg was selected as the
suitable amount of the catalyst for the CMC hydrolysis.
silica (Al–SiO2/RL) (Ma et al., 2011; Yao et al., 2006), rubber latex
bio-templated alumina (Al2O3/RL) (Ma et al., 2011) and commer-
cial Al2O3 (Table 1). Again, MIL-53(Al) exhibited significantly higher
activity. This may suggest that the large micropores, well-isolated
acid sites of MIL-53(Al) catalyst allow fast diffusion of the reactants
and thereby facilitating its catalytic reactivity (Lee et al., 2009).
Besides, compared to conventionally used mesoporous inorganic
materials, MOFs exhibit the potential for more flexible rational
design, by controlling the size and the functionalization of the
organic linkers (Li, Eddaoudi, O’Keeffe, & Yaghi, 1999). The well-
dispersed and effective catalytic sites can be introduced during
MOF’s framework construction, in the metal sites or organic links
(Song et al., 2011). Therefore, MOFs offer a new platform upon
which to generate a high density of active catalytic centers, achieve
good mass transport (Dau & Cohen, 2013).
In order to prove whether the catalyst is a heterogeneous one,
experiments with fast hot catalyst filtration had been done by a
modified process as Ma et al. (2011). The ICP-AES analysis of the
filtrates obtained from the fast hot catalyst filtration with negligible
amount of leaching of active aluminum species (≤0.001 wt%) was
detected. This indicated that the active component (aluminum) did
not leach to the solution and MIL-53(Al) did act as a heterogeneous
catalyst.
For heterogeneous catalytic reactions, a sufficient reaction time
and temperature are critical for achieving adequate mass trans-
portation in the reactions (Kuo et al., 2013). Fig. 5 shows that
MIL-53(Al) catalyst is efficient for CMC hydrolysis, and the reac-
tion temperature and time had a great effect on the 5-HMF yield.
The yield of the 5-HMF increased as the reaction temperature was
increased. However, when reaction temperature passed 473 K, CMC
converted to other products and 5-HMF was not detected. It has
been reported that 5-HMF is not very steady in high tempera-
ture water, and can be transformed into other substances (Lü, Li, &
Zhang, 2008). Therefore, 473 K was selected as the suitable reaction
temperature. Furthermore, it is clear that the yield of the 5-HMF
increased as the reaction time rose and passed through a maximum
at each temperature, respectivety. A further increase in the reac-
tion time resulted in significant decrease in the yield of the 5-HMF,
probably owing to 5-HMF being further converted to by-products.
The decomposition of 5-HMF to some products was also reported
(Chheda, Román-Leshkov, & Dumesic, 2007). The generation of by-
products was more rapid than that of 5-HMF at that time. Thus,
we suggest the optimal reaction temperature is 473 K and reaction
time to be 4 h in aqueous solvent system.
The hydrolysis of CMC to 5-HMF over different MOF catalysts
under same conditions are summarized in Table 1. Possible
products, 5-HMF and TRS, were identified, and their calibration
To study the recycling ability of MIL-53(Al) under the optimum
reaction conditions, recycling experiments were carried out. The
typical recycling procedure was as follows: after the initial reaction,
Table 1
a
Comparison of catalytic activities of different MOF catalysts for the hydrothermal decomposition of CMC to 5-HMF .
Catalyst
Temperature [K]
Time [h]
5-HMF yield [mol%]
TRS yield [mol%]
MIL-100(Cr)
MIL-101(Cr)
ZIF-8(Zn)
473
473
473
473
473
473
473
473
473
473
473
473
4
4
4
4
4
4
4
4
4
4
4
4
25.8
25.3
–
38.9
40.3
36.7
29.9
34.2
54.2
32.4
42.1
31.2
34.7
35.2
38.1
MOF-5(Zn)
UiO-66(Zr)
MIL-53(Al)
MIL-125(Ti)
HKUST-1(Cu)
Al–SiO2/RL
Al–TiO2/DDA
Commercial Al2O3
Al2O3/RL
–
24.5
40.3
30.9
31.8
24.0
28.6
18.6
18.4
a
Note: Reaction condition: substrate, 100 mg CMC; reaction time, 4 h; reaction temperature, 473 K; catalyst, 75 mg; solvent, H2O 80 mL.

1
50
G. Zi et al. / Carbohydrate Polymers 115 (2015) 146–151
Scheme 1. A possible reaction pathway for the hydrolysis of carboxymethyl cellulose over MIL-53(Al) catalyst.
the catalyst was separated from the reaction mixture by centrifu-
gation and washed with deionized water and ethanol, followed by
dryness at 473 K in an oven under vacuum for 12 h. Next, fresh CMC
and water were added to the recovered catalyst and then the sec-
ond run started. Similarly, the third run was also performed by
using the same procedure. The 5-HMF molar yield only slightly
dropped from the 40.3% to 39.1% and 38.4% with the first, sec-
ond and third run, respectively. The decrease of 5-HMF yield in
the recycle experiments can be attributed to the mass loss of the
catalyst in the washing steps and the blockage of active acid sites
by humins products. And the X-ray diffraction patterns of the fresh
and used MIL-53(Al) were almost similar verified the crystallinity
and stability of MIL-53(Al) after the catalytic reactions (Fig. 6). The
high thermal stability of MIL-53(Al) is in good agreement with the
literature (Loiseau et al., 2004).
Based on the above experimental results and the mechanisms
proposed for the hydrolysis of the cellulose in references (Deng
et al., 2012; dos Santos et al., 2013), a possible reaction pathway
for the hydrolysis of carboxymethyl cellulose over MIL-53(Al) cat-
alyst was depicted in Scheme 1. In the presence of a Brønsted acid
sites and water, a possible reaction mechanism could involve coor-
dination of carboxymethyl cellulose oxygen species to the metal
center activating bonds for subsequent reactions, such as hydrolysis
and degradation. First, the polymer chains of carboxymethyl cellu-
lose (a) are broken down into low molecular mass fragments and
ultimately to Al–glucose complex (b) by the action of an acid MIL-
before use
after use
30
10
20
40
2 Theta / degrees
Fig. 6. XRD patterns of MIL-53(Al) (before use and after use).
fructose. Moreover, furfural (f) and levulinic acid (g) are possible
by-product.
4. Conclusions
5
3(Al) catalyst. Then, Al species could coordinate with the hydroxyl
groups of glucose to form an enediol structure (c), which is con-
sidered as the key intermediate in the isomerization of glucose to
fructose (d). Finally, 5-HMF (e) can be obtained by dehydration of
In conclusion, the hydrolysis of CMC catalyzed by unfunction-
alized MIL-53(Al) with an environment-friendly chemical process
has been firstly studied. MIL-53(Al) with Brønsted acid sites has

G. Zi et al. / Carbohydrate Polymers 115 (2015) 146–151
151
been shown to be an efficient heterogeneous catalyst for the
hydrolysis of CMC to 5-HMF. At optimal reaction conditions, a
Liu, Y., Xiao, W., Xia, S., & Ma, P. (2013). SO3H-functionalized acidic ionic liq-
uids as catalysts for the hydrolysis of cellulose. Carbohydrate Polymers, 92,
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Loiseau, T., Serre, C., Huguenard, C., Fink, G., Taulelle, F., Henry, M., et al.
(2004). rationale for the large breathing of the porous aluminum
terephthalate (MIL-53) upon hydration. Chemistry—A European Journal, 10,
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5
-HMF molar yield of 40.3% and TRS molar yield of 54.2% were
obtained. The use of MOF catalyst in simple aqueous solvent sys-
tem opens up new opportunities to convert biomass resources to
high-value added chemical under relatively mild reaction condi-
tions. Moreover, MIL-53(Al) catalyst demonstrated here would be
extended to other acid-catalyzed reactions.
A
1
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Acknowledgments
Ogasawara, Y., Itagaki, S., Yamaguchi, K., & Mizuno, N. (2011). Saccharification
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The authors thank the National Natural Science Foundation of
China (Project NSFC-YN U1033603, 21263027, 21063016), and Pro-
gram for Innovative Research Team (in Science and Technology) in
University of Yunnan Province (IRTSTYN) for financial support.
519–525.
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