Cr-MIL-101-Encapsulated Keggin Phosphomolybdic Acid as a Catalyst for the One-Pot Synthesis of 2,5-Diformylfuran from Fructose

Article abstract of DOI:10.1002/cctc.201601546

The conversion of fructose into 2,5-diformylfuran (DFF) is a tandem reaction that consists of the dehydration of fructose to 5-hydroxymethylfurfural (HMF) catalyzed by an acid catalyst and subsequent oxidation of HMF to DFF by a redox catalyst. Phosphomolybdic acid encapsulated in MIL-101 (PMA–MIL-101), with high Br?nsted acidity and moderate redox potential, was evaluated as a promising catalyst for the one-pot synthesis of DFF directly from fructose. The results demonstrated that PMA–MIL-101 was an efficient and recyclable bifunctional catalyst for the production of DFF from fructose in DMSO; it showed high activity and selectivity towards the direct transformation of fructose into DFF, and it could be reused. A satisfactory DFF yield of 75.1 % was obtained over 2 PMA–MIL-101 in a one-pot, one-step reaction under optimal reaction conditions.

Full text of DOI:10.1002/cctc.201601546

Accepted Article
Title: Cr-MIL-101 encapsulated Keggin phosphomolybdic acid as
catalysts for one-pot synthesis of 2,5-diformylfuran from fructose
Authors: Jong-Min Lee
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of the final Version of Record (VoR). This work is currently citable by
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to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
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To be cited as: ChemCatChem 10.1002/cctc.201601546
Link to VoR: http://dx.doi.org/10.1002/cctc.201601546
A Journal of
www.chemcatchem.org

ChemCatChem
10.1002/cctc.201601546
Jun Zhao, Jayakumar Anjali, Yibo Yan, Jong-Min Lee*
School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, 637459, Singapore
KEYWORDS ： 5-hydroxymethylfurfural, 2,5-diformylfuran, metal-organic framework, biomass, phosphomolybdic acid
ABSTRACT: The direct conversion of fructose to 2,5-diformylfuran(DFF) is a tandem reaction which consists of fructose dehydra-
tion to 5-hydroxymethylfurfural(HMF) catalyzed by acid catalysts and subsequent oxidation of HMF to DFF by redox catalysts.
Phosphomolybdic acid encapsulated in MIL-101(PMA-MIL-101), with high Bronsted acidity and moderate redox potential, is
evaluated as a promising catalyst for the one-pot strategy for synthesizing DFF directly from fructose. The results demonstrate that
PMA-MIL-101 is an efficient and recyclable bifunctional for DFF production from fructose in DMSO, showing high activity and
selectivity towards direct transformation from fructose to DFF, and it can be reused. A satisfactory DFF yield of 75.1% is obtained
over 2PMA-MIL-101 in a one-pot and one-step reaction under optimal reaction conditions.
Bio-refining is an important approach for the current needs of
energy and chemicals for various applications. A growing
interest has been recently dedicated to obtaining these valuable
lyst-15 and Ru/HT,[19] CrCl
Fe -SBA-SO H and K-OMS-2, Amberlyst-15 and poly-
mer supported IBX amide
3 2 3 2
·6H O/NaBr and NaVO ·2H
O,[20]
[
10]
3
O
4
3
[
21]
have been investigated as bi-
[
1]
fuels and chemicals from biomass resources. Carbohydrates,
which can be generated from renewable biomass, are deemed
as promising feedstocks for the production of chemical build-
functional catalysts for the one-pot production of DFF from
fructose. However, since the oxidative catalysts can promote
the oxidative degradation of fructose and formation of humins,
in order to obtain the highest possible DFF yield, the oxidation
catalysts have to be added into the reaction after the fructose
has been converted to HMF in the presence of acidic catalysts,
resulting in a one-pot but two-step method conversion of fruc-
[
2]
ing blocks. 5-Hydroxymethylfurfural (HMF), which is ob-
tained from the acid catalyzied dehydartion of carbohydrates,
has been identified as a key platform chemical for the deep
exploitation and utilization of biomass resources due to its rich
[
3]
[10, 18]
chemical properties. The selective oxidation of hydroxyl
group of HMF leads to the formation of 2,5-Diformylfuran
tose to DFF.
Recently, it was noticed that heteropoly acids showed excel-
lent performance in acid and oxidation catalysis for the hydro-
(DFF), which is expected to be used as a monomer for poly-
meric materials and considered as a potential intermediate for
fungicides, heterocyclic ligands, furan-based resins and phar-
carbons. Keggin-type polyoxometalates, such as H
3 40
PW12O ,
and FePW12 40, have been applied in the dehydration of fruc-
O
[
4]
maceuticals.
[22]
tose to HMF. Moreover, Mo-containing Keggin heteropoly-
acids can also promote the aerobic oxidation of HMF to
The common synthetic methods of DFF were mainly based
on the selective oxidation of HMF. Various oxidants, such as
[
23]
DFF. However, heteropoly aicds can dissolve in most liq-
uids and form a homogeneous reaction system which causes
difficulties for the separation and reuse of the catalysts. In the
last decade, metal-organic-frameworks(MOFs) have attracted
numerous researchers’ attention in the world and were widely
NaOCl, BaMnO
4
, pyridinium chlorochromate, and 2,2,6,6-
tetramethylpiperidine-1-oxide were reported to be used in the
[
5]
oxidation of HMF to DFF. Typical catalysts, such as
[
6]
[7]
2
Co/Mn/Zr/Br, SiO -supported vanadylphosphate, Mn-salen,
[
8]
[9]
[10]
[11]
[12]
[24]
V
2
O
5
,
Ru/HT, K-OMS-2, Ru/C, Ag-OMS-2, PVP-
used in gas storage, drug delivery and dye adsorption. The
[
13]
[14]
[15]
[16]
Pd NP, VO
x
/TiO
2
2
,
Cu(NO
3
)
2
/VOSO
4
,
Fe
3
O
4
/Mn
3
O
4
chromium terephthalate metal–organic framework, MIL-101,
is one of the most porous materials reported to date. In addi-
tion, polyoxometalate(POM) can be introduced into the pores
of MIL-101 and generate a POM embedded MOF, which is
catalytically active towards oxidation of alkanes and al-
[
17]
and RuCo(OH)
CeO
2
exhibited good activity. However, to
produce DFF from HMF is an uneconomical and energy inten-
sive process because of the high price of HMF and the diffi-
culties in purification of HMF. Therefore, the industrial mass
production of DFF from HMF has not been realized.
[
25]
kenes. Very recently, phosphotungstic acid (PTA) encapsu-
lated into MOF exhibits good catalytic performance for acid-
The direct synthesis of DFF from carbohydrates provides an
alternative approach to overcome the above disadvantages.
The process involves a two-step reaction: dehydration of car-
bohydrates to HMF and oxidation of HMF to DFF, in which
the first step is an acid catalyzed reaction and the second one
is an oxidation reaction. Thus the combination of acidic cata-
lysts and oxidative catalysts were applied for the one-pot syn-
thesis of DFF from carbohydrates. For instance, H-form cati-
[
26]
catalyzed reactions, such as esterifications and dehydrations.
[
18]
on-exchange resin and vanadium based catalysts,
Amber-
Scheme 1. Conversion of fructose into HMF and DFF.
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ChemCatChem
10.1002/cctc.201601546
Herein, phosphomolybdic acid was encapsulated into MIL-
01(PMA-MIL-101) by a one-pot synthesis method and used
further increasing of PMA loading on MIL-101 did not bring
higher HMF yield due to the remarkable drop of the surface
area of the catalysts (Table S2). Higher PMA loading can
promote the dehydration of fructose to HMF but also lead to
the decrease of surface area and the pore size which are unfa-
vorable for the contact between the reactant and active sites,
and may lead to some diffusion limitations.
1
as bifunctional catalysts for the conversion of DFF from fruc-
tose in a one-pot and one-step approach (see supporting in-
formation). The Fourier Transform Infrared Spectroscopy
FTIR) (Figure S1), X-ray diffraction (XRD) measurement
Figure S2) and Raman spectra (Figure S3) confirmed the
(
(
formation of PMA-MIL-101 and MIL-101 retained its struc-
ture when the synthesis was carried out in the presence of
PMA. The fructose undergoes acid-catalyzed dehydration to
produce HMF and aerobic oxidation of HMF to form DFF
through the PMA-MIL-101 in ambient oxygen (Scheme 1).
Figure 2 HMF oxidation to DFF over PMA-MIL-101. Reac-
tion conditions: 30mg catalyst, 63mg HMF, 5mL DMSO,
o
O
2
=20mL/min, 140 C, 20h.
After the above study on fructose dehydration to HMF, the
aerobic oxidation of HMF to DFF was further investigated. In
a typical process, 0.5mmol HMF was dissolved in DMSO and
Figure 1. Catalytic dehydration of fructose to HMF over
PMA-MIL-101. Reaction conditions: 30mg catalyst, 200mg
fructose, 5mL DMSO, 110 C, 1h.
o
heated to 140 C with 30mg PMA-MIL-101 as catalysts for 20
o
h under an oxygen flow rate of 20mL/min. The catalytic per-
formance of PMA-MIL-101 in the aerobic oxidation of HMF
to DFF is shown in Figure 2. MIL-101 was widely used in the
Intimal experiments were conducted to study the catalytic
performance of PMA-MIL-101 catalysts toward fructose de-
hydration. In a typical process, 200mg of fructose was dis-
oxidation of hydrocarbons, such as cyclohexene, indane,
o
[30]
solved in 5mL DMSO and heated to 110 C with 30mg of
dibenzothiophene, et al.
According to the related reports,
PMA-MIL-101 as a catalyst. The catalytic reaction results
were shown in Figure 1. According to the related research
results, the interaction between DMSO and fructose can facili-
tate the selective dehydration of fructose to HMF. Besides,
DMSO can also help to protect HMF from further rehydration
the carboxylic acid groups in MIL-101 can activate molecular
[
31]
oxygen. In addition, it is reported that the acids formed by
the thermolysis of DMSO may act as catalysts in HMF oxida-
[
27a]
tion.
HMF conversion of 65.1% and DFF yield of 47.2%
was obtained when pure MIL-101 was used as the catalyst in
Figure 2. Keggin-type heteropoly acids were reported to be
[
27]
to formic acid and levulinic acid. Thus, it can be seen in
Figure 1 that fructose can be converted to HMF without any
acid catalysts. Since MIL-101 contains coordinatively unsatu-
rated meatal centers as Lewis acids and also catalytically ac-
tive sites suspended on the organic linkers, the addition of
[
32]
effective in the aerobic oxidation of HMF to DFF. A HMF
conversion of 90.8% and DFF yield of 88.2% were obtained
when PMA was used as the catalysts (PMA dosage is the same
as the PMA loading on 2PMA-MIL-101), indicating the high
activity of PMA on the oxidation of HMF to DFF. The rela-
tionship between the activity of PMA-MIL-101 and the PMA
loading was investigated. Importantly, when the MIL-101
supported PMA catalysts were applied in the reaction, the
yield of DFF and HMF conversion enhanced greatly compared
with MIL-101. 87.5% HMF conversion and 82.6% DFF yield
were obtained when 0.5PMA-MIL-101, with a PMA loading
of 9.5%, was used as the catalyst. The selectivity of DFF in-
creased from 72.6% (MIL-101) to 94.4%(0.5PMA-MIL-101).
With increasing the loading of PMA, the yield of DFF in-
creased, reaching a maximum of 91% (2PMA-MIL-101), and
then decreased to 81.7% (3PMA-MIL-101) due to the decline
of surface area and pore size in this process (Table S2).
[
28]
MIL-101 increased the reaction speed. Bronsted acids are
also active for the dehydration of carbohydrates especially for
[
29]
the conversion of fructose to HMF. Therefore, the reaction
process is further accelerated when PMA-MIL-101 was ap-
plied as catalysts and the fructose conversion and DFF yield
increased as the loading amount of PMA raised. Obviously,
0
.5PMA-MIL-101, with a PMA loading of 9.5%, was more
active than pure MIL-101. After one-hour reaction, the HMF
yield was 44%. HMF yield of 60.1% was obtained when the
PMA loading increased to 10.4%. To further confirm the ac-
tivity of PMA, the reaction was carried out in the presence of
PMA (PMA dosage is the same as the PMA loading on
2
PMA-MIL-101). A fructose conversion of 81% and DFF
yield of 64% were obtained, indicating the good activity of
PMA on the dehydration of fructose to HMF. However, the
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ChemCatChem
10.1002/cctc.201601546
Figure 4. Fructose conversion into HMF and DFF as a func-
tion of reaction time. Reaction conditions: fructose 200mg,
Figure 3. One-pot and one-step synthesis of DFF from fruc-
o
catalytic 40mg, DMSO 5mL, O
2
=20mL/min, 150 C.
tose. Reaction conditions: 40mg catalyst, 200mg fructose,
o
The time course for the one-pot and one-step conversion of
fructose to DFF was investigated by determining the change of
the content of fructose in Figure 4, HMF and DFF in specified
time intervals during the reaction process. It is well known
that the reaction consists of two steps: the dehydration of fruc-
tose to HMF and the aerobic oxidation of HMF to DFF. Under
the combined action of DMSO and Bronsted and Lewis acid
of PMA-MIL-101, HMF formed quickly, reaching a maxi-
mum yield in 0.5h. Then the reaction entered the second step,
5
mL DMSO, O
2
=20mL/min, 150 C, 7h.
PMA-MIL-101 was used as the bifunctional catalyst in the
one-pot and one-step synthesis of DFF from fructose. In a
typical experiment, 200mg fructose was dissolved in 5 mL
o
DMSO with 40mg PMA-MIL-101 and then heated to 150 C,
with oxygen bubbling at a rate of 20 mL/min. The experiment
results are showed in Figure 3. In the presence of MIL-101,
o
HMF was the main product after the reaction for 7h at 150 C
due to the limited catalytic oxidation ability of MIL-101, giv-
ing a HMF yield of 54.1% and DFF yield of 13.6%. As ex-
pected, the DFF yield increased significantly after the loading
of PMA on the MIL-101. When 0.5PMA-MIL-101 was added
as the catalyst, the DFF yield reached 52.22% and HMF yield
declined noticeably from 54.1% (MIL-101) to 3.2%. Further
increasing the PMA loading afforded full HMF conversion
and higher DFF yield. DFF yield of 75.1% was achieved when
in which HMF was continuously consumed and the yield of
3-
DFF increased accordingly. [PMo12
O
40
]
was reported to be
the active species which promoted the cleavage of the O-H
bond in the hydroxyl group and cleavage of the C-H bond in
[32]
the methylene group of HMF in this step. The successful
synthesis of DFF from fructose was attributed to the excellent
tolerance of PMA to organic by-products in the reaction sys-
tem and moderate redox ability of PMA which might other-
wise lead to the strong decomposition of fructose and HMF
resulting in a large number of by-products.
2
PMA-MIL-101 was used as a catalyst under the same reac-
tion conditions. Similar to the reaction results of fructose de-
hydration to HMF and HMF oxidation to DFF, the yield of the
target product increased with the increasing of PMA loading,
reaching a maximum value and then decreased slightly. In
addition, the color of the reaction solution turned from green
or light green before the reaction to dark brown after the reac-
tion, indicating the formation of humins due to the degradation
of HMF and the oxidation of fructose in the initial stage of the
reaction, which is supposed to lead to a low carbon balance.
Table 1 Fructose conversion to DFF under different reaction conditions.
o
Entry
Catalyst (mg)
T( C)
140
150
150
150
150
160
t(h)
Fructose conv. (%)
HMF yield(%)
DFF yield(%)
53.4
1
2
3
4
5
6
40
20
40
60
80
40
7
100
100
100
100
100
100
26.5
14.1
0.8
7
69
7
75.1
5
3.1
72.4
5
4.9
70.2
2
27.3
53.9
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ChemCatChem
10.1002/cctc.201601546
7
40
160
5
100
0
73.8
Reaction conditions: fructose 200mg, O
2
=20mL/min.
In the presence of 2PMA-MIL-101, the reaction conditions
affecting the catalytic performance were investigated and the
results were summarized in Table 1. It can be seen that the
yield of the products was greatly affected by the reaction time,
fructose, the reduction of the catalyst amount with the increase
of the reuse cycles mainly influences the oxidation of HMF to
DFF. Therefore, more and more HMF remained in the reaction
products, resulting in the decrease of DFF yield. After the
second run, the DFF yield decreasing was slowed down grad-
ually and the catalytic performance tended to become stable.
reaction temperature and catalyst amount. A HMF yield of
o
2
6.5% and DFF yield of 53.4% were obtained in 7h at 140 C
(
Entry 1), while a comparable result was achieved in only 2h
In conclusion, considerable efforts have been made to the
synthesis of DFF from fructose by a one-pot and one-step ap-
proach in recent years. However, it is still challenging to
achieve a satisfactory DFF yield due to the difficulties in gen-
erating acid sites and oxidative active sites on one support to
form bifunctional catalysts, and reduce the side-reactions
meanwhile. In this study, phosphomolybdic acid was encapsu-
lated in a metal-organic framework MIL-101 and used as a
bifunctional catalyst for the direct transformation of fructose
to DFF. The as-synthesized catalysts processed both Bronsted
acidity and oxidability, which synergistically facilitated the
dehydration of fructose and the aerobic oxidation of HMF.
PMA loading is a key factor which influences the catalytic
performances. Under optimal reaction conditions, a DFF yield
of 75.1% was achieved over 2PMA-MIL-101 after 7h in
DMSO. The catalyst could be recycled and reused without
significant loss of the catalytic activity. This one-pot and one-
step synthesis of DFF from fructose highlights a good prospect
for lower costs and energy consumption in biomass carbohy-
drate conversion without separation of reaction intermediates.
o
when it was reacted at 160 C (Entry 6), and all the HMF can
be converted to DFF in 5 h (Entry 7), resulting in a final DFF
yield of 73.7%. Our previous study on the dehydration of fruc-
tose to HMF by using PMA-MIL-101 has proven that the de-
hydration step runs fast under the investigated temperature
range, so the reaction temperature affects the final yield of
DFF by affecting the reaction rate of HMF oxidation to DFF.
A 14.07% HMF yield and 69% DFF yield were obtained in 7h
o
when a 20mg catalyst was applied in the reaction under 150 C
(Entry 2), while an above 70% yield of DFF with little HMF
remains can be achieved in even shorter time by increasing the
catalyst amount to 40, 60 and 80mg (Entry 3,4,5). Overall, the
results showed that the catalytic performance was steady.
Supporting Information. Experimental details, Table S1-S2
and Figures S1-S3.
*
Telephone: +65-6513-8129. Fax: +65 6794-7553. E-mail:
jmlee@ntu.edu.sg.
This work is supported by the National Research Founda-
tion (NRF), Prime Minister’s Office, Singapore under its
Campus for Research Excellence and Technological Enter-
prise (CREATE) program, as well as the AcRF Tier 1 grant
Figure 5. Reusability of 2PMA-MIL-101 with the reaction
conditions described in Figure 3.
The reusability and stability of PMA-MIL-101 was investi-
gated in the one-pot and one-step conversion of fructose to
DFF. The used catalyst was separated from the reaction mix-
ture by centrifugation, and washed by ethanol and deionized
(
RGT27/13), Ministry of Education, Singapore.
water, respectively. The wet catalyst was dried in an oven at
o
6
5 C overnight. Generally, the catalyst affords stable perfor-
mance and the fructose conversion maintained at almost 100%
during the recycling test in Figure 5. However, there was a
drop of DFF yield to about 10% in the second run. The ICP
analysis of the filtrate after the catalytic reaction showed a 9%
loss of the Mo in the catalyst. This loss could be caused by the
leaching of Mo from the catalyst and the loss of the very fine
particles of PMA-MIL-101 due to the stirring during the recy-
cling reaction. The loss of the catalyst during the recycling
operation was another reason behind the decrease of the DFF
yield. Since the dehydration of fructose to HMF runs fast and
the reaction time was long enough for the fully conversion of
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