Biomass into chemicals: One-pot production of furan-based diols from carbohydrates via tandem reactions

Article abstract of DOI:10.1016/j.cattod.2014.02.029

In this work, the direct production of furan-based diols from carbohydrates and their upstream raw materials via one-pot tandem reactions in ionic liquid/water system is presented. In this novel reaction system, ionic liquid serves as an advantageous solvent for polysaccharide (cellulose, inulin, sucrose) hydrolysis and hexose dehydration reactions, and heterogeneous Pd, Pt, Ir, Ni, Ru-based catalysts catalyze HMF hydrogenation reaction under relatively mild condition (50 °C, 6 MPa H₂) to afford moderate to high yield (34.0-89.3%) of furan-based diols, namely, 2,5-dihydroxymethylfuran (DHMF) and 2,5-dihydroxymethyltetrahydrofuran (DHMTF). Our results show that the metal species strongly affects the selectivity of the products, while the nature of the support influences the activity of the catalysts significantly. By selecting the proper metal species and the support, controllable production of DHMF or DHMTF was realized. Based on the intermediates identified and the conversion results, the proposed reaction pathway, including possible side reactions were presented. Taken together, our catalytic system featured with simple process, mild condition, high yield of diols and adjustable product selectivity. The direct conversion of the carbohydrates and the upstream materials drives our technology nearer to real application for cost-efficient production of chemicals from biomass.

Full text of DOI:10.1016/j.cattod.2014.02.029

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Catalysis Today
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Biomass into chemicals: One-pot production of furan-based diols
from carbohydrates via tandem reactions
Haile Caia,b, Changzhi Li , Aiqin Wang , Tao Zhang
a
a
a,∗
a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, CAS, 457 Zhongshan Road, Dalian, Liaoning, 116023, P. R. China
University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, the direct production of furan-based diols from carbohydrates and their upstream raw
materials via one-pot tandem reactions in ionic liquid/water system is presented. In this novel reac-
tion system, ionic liquid serves as an advantageous solvent for polysaccharide (cellulose, inulin, sucrose)
hydrolysis and hexose dehydration reactions, and heterogeneous Pd, Pt, Ir, Ni, Ru-based catalysts cat-
Received 15 November 2013
Received in revised form 11 February 2014
Accepted 13 February 2014
Available online xxx
◦
alyze HMF hydrogenation reaction under relatively mild condition (50 C, 6 MPa H2) to afford moderate
to high yield (34.0–89.3%) of furan-based diols, namely, 2,5-dihydroxymethylfuran (DHMF) and 2,5-
dihydroxymethyltetrahydrofuran (DHMTF). Our results show that the metal species strongly affects the
selectivity of the products, while the nature of the support influences the activity of the catalysts sig-
nificantly. By selecting the proper metal species and the support, controllable production of DHMF or
DHMTF was realized. Based on the intermediates identified and the conversion results, the proposed
reaction pathway, including possible side reactions were presented. Taken together, our catalytic system
featured with simple process, mild condition, high yield of diols and adjustable product selectivity. The
direct conversion of the carbohydrates and the upstream materials drives our technology nearer to real
application for cost-efficient production of chemicals from biomass.
Keywords:
2
2
,5-dihydroxymethylfuran
,5-dihydroxymethyltetrahydrofuran
Biomass
Hydrogenation
Ionic liquids
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
the manufacture of polyesters and heat insulating material, which
are currently produced predominantly from petroleum resource
[6–8]. Theoretically, this kind of diols could be generated from
hexoses and their upstream materials, such as oligosaccharides,
inulin and cellulose, as well as the raw biomass via hydrolysis,
dehydration and subsequently selective hydrogenation reactions
(Scheme 1). However, each step in the whole process is typically
complex and includes severe side reactions [1,7,9]. In addition,
the low selectivity makes the separation and purification of the
intermediate products a big problem. To improve the conversion
efficiency, a great number of studies focus individually on polysac-
charide (including cellulose) hydrolysis, hexoses dehydration and
Biomass is renewable candidate that assumes the potential
to serve as a sustainable feedstock in lieu of diminishing fossil
resources, for future biofuels and chemicals [1]. With the increasing
cost of fossil fuels and the concerns related to their environmental
impact and greenhouse gas effect, extensive research and develop-
ment programs have been initiated worldwide to convert biomass,
such as forestry wastes, agricultural residues and energy crops, into
valuable products [2–5].
Furan-based diols 2,5-dihydroxymethylfuran (DHMF) and 2,5-
dihydroxymethyl-tetrahydrofuran (DHMTF) are bulk chemicals in
5
-hydroxymethylfurfural (HMF) hydrogenation reactions.
For instance, to make ˇ-1,4-glycosidic bonds in cellulose more
accessible to chemical transformation, ionic liquids (ILs) [10–12]
that capable of dissolving cellulose, and robust solid acids [13–18]
are applied in cellulose hydrolysis reaction and some good results
are obtained. In the dehydration step, improved performances have
also been made for both ketohexose (e.g. fructose) and aldohex-
ose (e.g. glucose) conversion to afford 5-hydroxymethylfurfural
Abbreviations: DHMF, 2,5-dihydroxymethylfuran; DHMTF, 2,5-dihydroxy-
methyltetrahydrofuran; ILs, ionic liquids; HMF, hydroxymethylfurfural; [BMIm]Cl,
-butyl-3-methylimdazolium chloride; [EMIm]Cl, 1-ethyl-3-methylimdazolium
chloride; HT, hydrotalcite.
∗ Corresponding author at: Dalian Institute of Chemical Physics, Chinese Academy
of Sciences, 457 Zhongshan Road Dalian 116023, China. Tel.: +86 411 84379015;
fax: +86 411 84691570.
1
(HMF) in homogeneous or heterogeneous systems including water,
E-mail address: taozhang@dicp.ac.cn (T. Zhang).
organic solvents, ILs [19,20], and two-phase solvents [21] with liq-
uid acids, solid acids and metal chloride (CrCl2, CrCl3, GeCl4, etc.)
URLs: http://www.taozhang.dicp.ac.cn (T. Zhang), http://www.dicp.cas.cn
T. Zhang).
(
http://dx.doi.org/10.1016/j.cattod.2014.02.029
920-5861/© 2014 Elsevier B.V. All rights reserved.
0
Please cite this article in press as: H. Cai, et al., Biomass into chemicals: One-pot production of furan-based diols from carbohydrates
via tandem reactions, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.029

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2
Scheme 1. Schematic illustration of the steps from biomass-derived carbohydrates to furan-based diols DHMF and DHMTF.
and other catalysts [22]. In addition, hydrogenation of HMF and fur-
fural to valuable furan-based alcohols, such as DHMF [23], DHMTF
24,25] furfuryl alcohol, and tetrahydrofurfuryl alcohol [26] have
been reported with various metallic catalysts. In despite of these
progresses, mainly because of the low selectivity and incompati-
ble reaction conditions of each step, few literature succeed in the
direct conversion of carbohydrates and their upstream raw materi-
als to produce furan-based diols. As a similar example, Bell’s group
transformation, the reaction solution was filtered and the clear fil-
trate was analyzed by HPLC.
[
The HPLC analysis of the products was conducted on Agilent
1100 with a Shodex SC-101 column, using extra-pure water as
mobile phase at a flow rate of 0.6 ml/min, the pressure of col-
◦
umn was 28 bar, the column temperature was 45 C. The yields
of HMF was calculated by the equation: Yield (%) = (molar num-
ber of HMF)/(molar number of fructose) × 100. The conversion of
HMF was calculated by the equation: Conversion (%) = (1 − (molar
number of the left HMF)/(molar number of HMF from sub-
strates)) × 100. The selectivity of DHMF or DHMTF were calculated
by the equation: Selectivity (%) = (molar number of the prod-
uct)/(molar number of converted HMF) × 100. Total selectivity
of furan-based diols was calculated by the equation: Selectivity
(%) = (Selectivity of DHMF) + (Selectivity of DHMTF). Total yields
of furan-based diols were calculated by the equation: Total yield
(%) = (Yield of HMF) × (Conversion of HMF) × (Total selectivity of
furan-based diols) × 100.
[
27] realized the two-step approach for the catalytic conversion
of glucose to 2,5-dimethylfuran in ionic liquid/CH CN mixture.
3
In their study, heteropoly acid 12-molybdophoric acid exhibited
exceptionally activity for the dehydration of glucose to HMF, the
extracted HMF then underwent hydrogenation reaction in 1-ethyl-
3
-methylimdazolium chloride [EMIm]Cl/CH CN mixture to obtain
3
2
,5-dimethylfuran (DMF) with the yield of 15% [27].
In this work, direct production of furan-based diols DHMF and
DHMTF from carbohydrates and their upstream materials via one-
pot tandem reactions in IL/water system is presented. In this novel
reaction system, IL serves as efficient medium for polysaccharide
(
cellulose, inulin) hydrolysis and hexose dehydration reactions, and
3
3
3
. Results and discussion
heterogeneous Pd, Pt, Ir, Ni, Ru-based catalysts catalyze HMF hydro-
genation reaction under relatively mild condition (50 C, 6 MPa H )
to afford moderate to high yield (34.0–89.3%) of furan-based diols.
More importantly, after exploring the effects of the metal species
and the supports on the products distribution, selectively produc-
tion of DHMF or DHMTF from fructose is realized.
◦
2
.1. Optimization reaction conditons
.1.1. Fructose dehydration in ionic liquids
As introduced above, the direct conversion of carbohydrate to
DHMF and DHMTF includes several reaction steps. In order to cou-
ple the individual reactions, taking fructose as the substrate, we first
explored the dehydration reaction to obtain HMF. In our previous
study [20], we presented an efficient strategy for selective produc-
tion of HMF from concentrated fructose in ILs under microwave
irradiation without addition of catalysts. Considering that conven-
tional oil-bath heating is simple and more available, in this study,
we tried the catalyst-free dehydration reaction in IL [BMIm]Cl with
oil-bath heating. The results are shown in Fig. 1. It was found that
although fructose conversion was laggardly at low temperature of
2
. Experimental
2
.1. Materials
Fructose (99%), inulin and microcrystalline cellulose (extra pure,
average particle size 90 ␮m) were purchased from Acros Organics.
Glucose (AR) was bought from Tianjin Kemiou Chemical Reagent
Co., Ltd. All the other chemicals were obtained from local supplier
and were used as received without further purification.
Supported transition-metal catalysts including Pd/C, Ir/C, Pt/C,
Ru/C, Ni/C, Pd/Al O , Pd/SiO , Pd/TiO , and Pd/HT were prepared
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
2
3
2
2
by means of incipient wet impregnation followed by reduction in
◦
H2 at 300 C. The nominal transition-meta loadings were 5 wt%.
o
1
-butyl-3-methylimdazolium
EMIm]Cl were prepared according to our previous study [11],
the water content was determined as (0.0975 ± 0.0005)% and
0.1275 ± 0.0005)%, respectively, through Karl–Fischer titration.
chloride
([BMIm]Cl)
and
1
1
00 C
o
[
15 C
o
130 C
(
o
1
45 C
2.2. Typical conversion process of fructose for the production of
DHMF and DHMTF
A typical process for the catalytic production of furan-based
diols is as follows: 0.18 g fructose and 0.5 g [BMIm]Cl was charged
◦
in an open autoclave and was heated to 130 C for 20 min to afford
HMF. About 20 mg samples were withdrawn, weighed, quenched
with cold water, and subjected to HPLC analysis. 35 ml cool water
and 50 mg metal catalyst were added to the residue reaction mix-
ture. After the solution was mixed uniformly, the hydrogenation
0
10
20
30
40
50
60
Time (min)
reaction was carried out with an initial H pressure of 6 MPa (mea-
sured at room temperature) at 50 C for set time. After the one-pot
2
Fig. 1. Fructose dehydration results in [BMIm]Cl. Reaction condition: 0.7 g fructose,
2.0 g [BMIm]Cl, 130 C.
◦
◦
Please cite this article in press as: H. Cai, et al., Biomass into chemicals: One-pot production of furan-based diols from carbohydrates
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◦
1
00 C, elevating the reaction temperature would accelerate the
(a)
1
00
100
80
60
40
20
0
transformation of fructose to HMF effectively. For example, the
DHMTF
DHMF
◦
◦
dehydration reaction at 130 C and 145 C afforded HMF in 78%
and 75% yields, within 20 min and 10 min, respectively, indicating
that the reaction temperature is very crucial for fructose dehy-
dration reaction in ILs. Further prolonging the reaction time could
not enhance HMF yield, while the color of the mixture turns dark,
suggesting the formation of black humins. As fructose dehydra-
tion reaction in aqueous solution is inert if no catalyst used [28],
BMIm]Cl plays the role not only as the appropriate solvent but
also as the advantageous promoter for HMF production. Noting
that 20 min is enough for fructose dehydration reaction at 130 C, in
the following one-pot tandem conversion of carbohydrates experi-
80
6
0
0
4
[
◦
20
0
◦
ments, carbohydrate dehydration reactions are conducted at 130 C
for 20 min and then subject to next in-situ hydrogenation step.
2
4
6
Initial hydrogen pressure/MPa
3.1.2. In-situ hydrogenation reaction
When the aforementioned fructose dehydration reaction was
1
00 (b)
100
proceeded 20 min, it was quenched with cold water and in-situ
hydrogenation of HMF was performed over Pd/C catalyst under
hydrogen pressure. Fig. 2(a) shows the conversion of HMF and
the selectivity to diols as a function of initial hydrogen pressure.
It was found that higher reaction pressure would enhance the
activity, leading to the increased conversion of HMF and selectiv-
ity of diols. Under the H2 pressure of 2 MPa, only 43.6% of HMF
was consumed in 3 h, and the selectivity to furan-based diols was
totally 76.1%, with DHMF 41.5% and DHMTF 34.6%, which suggested
that hydrogenation of most aldehyde groups and partially satura-
tion of the furan rings occurred with the consumed HMF. Upon
increasing the H2 pressure from 2 MPa to 4 MPa, HMF was nearly
completely converted, leading to increased DHMTF selectivity from
80
80
60
40
20
0
DHMF
DHMTF
6
0
0
4
20
0
3
4.6% to 69.3%, while the selectivity of DHMF was decreased to
.2%. Further increasing the H2 pressure to 6 MPa resulted in pre-
1
h
2 h 3 h
0.025 g
1 h 2 h 3 h
0.05 g
1 h 2 h 3 h
0.100 g
3
dominant DHMTF with the selectivity up to 84.2%, implying that
most of DHMF and the intermediates such as (2,3-dihydrofuran-
5 wt% Pd/C amount
2
,5-diyl)dimethanol were converted to DHMTF. It is interesting to
(
c)
1
00
100
80
60
40
20
0
note that this result is quite different from that obtained by Bell
[
27]. In their recent work, Pd/C catalyzed HMF conversion under
◦
6
.2 MPa H2 pressure at 120 C in [EMIm]Cl/CH CN afforded DMF
3
80
60
as the main product, but the transformation efficiency was rela-
tively low (conversion: 47%, DMF selectivity: 32%). To make clear
the difference, we tested an additional HMF hydrogenation reac-
tion using [EMIm]Cl/H O as the medium. The reaction over 0.05 g
Pd/C at 50 C for 3 h under 6 MPa H pressure also afforded result
DHMTF
DHMF
2
◦
2
4
0
0
0
(
conversion: 100%, DHMTF selectivity: 93%) quite different from
that in [EMIm]Cl/CH CN, whereas similar to that in [BMIm]Cl/H O.
3
2
◦
Increasing the reaction temperature to 120 C could not shift the
product selectivity from furan-based diols (DHMF and DHMTF) to
DMF. Obviously, the other part of the solvent mixture plays a key
role in determination of the products selectivity, i.e. protic H O
leads to the formation DHMF and DHMTF, while the dipolar aprotic
2
2
25
50
80
100
200
o
Hydrogenation temperature/ C
solvent CH CN tends to form DMF. Taken together, in comparison
3
with literature [27], greener solvent H O used in our reaction ren-
ders this catalytic system both efficient and more environmentally
friendly.
Fig. 2b shows the influence of the catalyst amount on the
hydrogenation reaction performance. The trend is somewhat dif-
2
Fig. 2. One-pot conversion of fructose. (a) Effect of the H2 pressure on the hydro-
◦
genation reaction over 0.05 g Pd/C at 50 C for 3 h. (b) Effect of the catalyst amount
◦
and reaction time on the hydrogenation reaction at 50 C under 6 MPa H2. (c) Effect of
the reaction temperature on the hydrogenation reaction. Condition: 0.05 g 5% Pd/C,
6
MPa H2, 3 h. In all the reaction processes, the dehydration reaction was conducted
◦
in 0.5 g [BMIm]Cl at 130 C with 0.18 g fructose for 20 min, then 35 ml water and 5%
Pd/C catalyst were added in the mixture for the hydrogenation reaction.
ferent from that obtained at various hydrogen pressures. Under
◦
the given condition (50 C, 6 MPa H ), 0.025 g Pd/C is enough for
2
HMF complete conversion, suggesting that the conversion is not
affected by the catalysts concentration. However, increasing both
the catalyst amount and reaction time could change the diols’
distribution and enhance the selectivity of DHMTF clearly. For
instance, DHMTF selectivity enhanced from 48.7% to 84.2% over
could be totally hydrogenated, giving DHMTF as a predominant
product. On the other hand, side reactions such as ring-opening
reaction, rehydration reaction, and hydrodeoxygenation reaction
may also occur, making the selectivity of furan-based diols slightly
decreased. Therefore, 0.05 g catalyst is selected in the following
hydrogenation reactions.
0.05 g Pd/C in 3 h compared to 0.025 g Pd/C in 1 h. If 0.10 g cata-
lyst was used, both aldehyde groups and the furan rings in HMF
Please cite this article in press as: H. Cai, et al., Biomass into chemicals: One-pot production of furan-based diols from carbohydrates
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On the whole, one may clearly see that conversion attains a max-
imum with the increasing hydrogen pressure (Fig. 2a), while as it
is not affected by the catalysts concentration (Fig. 2b). Therefore,
mass transfer (or hydrogen solubility) is possibly controlling the
overall rate of the reaction.
To obtain high yield of furan-based diols, hydrogenation reac-
tion was also conducted at different temperature, the results are
shown in Fig. 2c. As a typical hydrogenation catalyst, Pd/C shows
HMF yield
DHMTF selectivity
DHMF selectivity
1
20
HMF conversion
100
80
6
0
0
strong activity in IL/water mixture for HMF hydrogenation reaction,
◦
under mild conditions of 25 C and 6 MPa H , HMF was consumed
2
4
nearly completely in 3 h to afford total diols selectivity 85.8% (39.2%
of DHMF and 46.6% of DHMTF). Raising the reaction temperature
◦
◦
◦
20
0
to 50 C, 80 C and 100 C could eventually simultaneously hydro-
genate all the unsaturated bonds in HMF to obtain exclusively
DHMTF, and the total selectivity of diols are 84%, 88.1% and 91.4%,
◦
1h 3h
Pd/C
1h 3h
1h 3h
1h 3h
Pd/TiO 2
1h 4h
Pd/HT
respectively. Much higher reaction temperature of 200 C could
Pd/Al O
Pd/SiO 2
2
3
lead to severe side reactions mentioned before that decrease the
yield of target products. It is worthy of notice that even at this high
temperature, only trace DMF was formed (less than 2%), implying
that dehydroxylation reaction is hard to occur in our system. There-
fore, it is easy to control the products to furan-based diols, which is
one of the unique features of this work over most existing methods.
Taking into account of the reaction efficiency and the convenience
of the operation, 50 C is selected for hydrogenation reaction since
this low temperature could avoid the formation of by-products and
without compromising the diols yield.
It should be noted that in most of the above hydrogenation reac-
tions, DHMTF was the main product; even under relatively mild
condition, it is hard to stop the reaction in the DHMF stage, sug-
gesting that Pd/C is an active catalyst for both the aldehyde group
and furan ring hydrogenation reactions to produce DHMTF.
Fig. 3. Production of furan-based diols from fructose via one-pot tandem reaction.
Reaction conditions: the dehydration reaction was first conducted in [BMIm]Cl at
◦
130 C with 0.18 g fructose for 20 min to afford HMF. Then 35 ml water and 0.05 g
catalyst were added into the reactor for hydrogenation reaction under 6 MPa H2 at
◦
50
C.
◦
oxygen vacancies) [30] at the palladium-titania interfacial region
which can coordinate the oxygen atom of the C O group via a lone
pair of electrons and thus, activate the C O group for the selec-
tive hydrogenation reaction [29,30]. Therefore, by dispersing on
the reductive support TiO , metal catalyst exhibits the potential
2
for selectively hydrogenating the carbonyl group while leaving the
C
C bond unchanged to afford DHMF. This viewpoint will be further
proved in Section 3.3.
As for Pd/HT catalyst, it is found that the basic HT support
not only restrains the dehydration reaction, but also significantly
inhibits the hydrogenation activity of Pd. Under the identified reac-
tion conditions, the conversion of HMF in 1 h is distinctly decreased
to 69.7% in comparison with the nearly quantitative conversion of
HMF in Pd/C catalyzed reaction. Even we prolonged the reacting
time to 4 h, HMF could not be completely consumed. On the other
hand, nitrogen physisorption showed that HT possessed the small-
est surface area (ESI, Table S1), implying the lowest metal active
sites were exposed. Accordingly, the activity of Pd/HT was relatively
low. In addition, it is reported that HT could induce ring-opening,
C–O dissociation reactions and other side reactions [23,31]. As a
result, the combined selectivity of DHMF and DHMTF was remark-
ably lower than 50%. Overall, due to its basic property and low
surface area, HT is not the preferred support in our reaction system
for fructose dehydration and subsequent hydrogenation reactions
to produce furan-based diols.
3
.2. One-pot tandem reactions of carbohydrates: support effects
with palladium catalyst
Previous studies indicate that the activity of the supported cata-
lyst strongly depends on the property of the support [29]. With the
aim to explore the support effect and further control the products
distribution, Pd dispersed on various supports, including ꢀ-Al O3
and SiO , TiO and Mg-Al hydrotalcite (HT), are synthesized and
applied in the direct transformation of fructose. It is known that
the fructose dehydration step is a typical acid-catalyzed reaction,
however, the weak acidic ꢀ-Al O3 and SiO2 supported palladium
catalysts did not enhance catalytic activity obviously compared to
the neutral supports TiO and active carbon. The yields of HMF were
between 74% and 80% over the four catalysts (Fig. 3), which were in
the same level with that of thermal reaction. This result is similar
to our previous study that the weak mineral acid could not pro-
mote fructose dehydration reaction in ILs [29]. On the other hand,
the basic HT inhibited the dehydration reaction with HMF yield
decreased to 60.7%.
2
2
2
2
2
3.3. Production of furan-based diols: effect of metal species
In the hydrogenation step, these supports showed different
Studies were carried out to control the product selectivity by
changing the nature of the metal component in the one-pot tandem
reactions. All the reactions are started from fructose via one-
pot two-step process: first, 20 min of the dehydration reaction in
effects on the catalytic activity. The acidic Pd/ꢀ-Al O3 and Pd/SiO2
2
embodied similar activities as that of Pd/C, HMF almost completely
transformed in 1 h. However, the selectivity to diols was a little bit
lower and the proportion of DHMTF was higher than those of Pd/C,
which means the product selectivity is sensitive to the acidity of
the support. If the reactions were prolonged to 3 h, the C C bond in
DHMF could be further saturated, and the final products are dom-
◦
[BMIm]Cl at 130 C, and then, 3 h of hydrogenation reaction under
◦
6 MPa H2 at 50 C. It is found in Table 1 that using either carbon
supported palladium or ruthenium as the catalyst, HMF could be
completely consumed to afford diols’ selectivity and yield of ca.
88% and 66% (entries 1–2), respectively. However, the distribu-
tions of the diols are different. Deep hydrogenated product DHMTF
(selectivity: 84.2%, yield based on fructose: 63.4%, see in entry 1)
dominated in the case of Pd/C, while carbonyl hydrogenated com-
pound DHMF (selectivity: 52.4%, entry 2) was the major product
for Ru/C. For Ir/C catalyst, although HMF conversion and furan-
based diols’ selectivity could reach 93% and 83.8% respectively,
inant DHMTF. In the case of Pd/TiO , it is important to point out
2
that although the conversion of HMF and the combined selectivity
to diols were similar to those of Pd/C, nearly half of the reaction
was stopped at DHMF stage under the same conditions in 1 h, a
longer reaction time (3 h) did not significantly change the products
distribution. It is possibly because that the interaction between the
3+
reductive support and metal created a special defect sites (Ti or
Please cite this article in press as: H. Cai, et al., Biomass into chemicals: One-pot production of furan-based diols from carbohydrates
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Table 1
a
One-pot production of furan-based diols from fructose over various metal catalysts .
Entry
Catalyst
HMF yield/%
HMF conversion/%
Selectivity/%
DHMF
Yield of diols/%
DHMTF
Total
1
2
3
4
5
6
5% Pd/C
5% Ru/C
5% Ir/C
5% Pt/C
5% Ni/C
5% Ir/TiO2
75
75
75
75
76
75
>99
>99
93
89
66
4
84 (63)b
36
14
8
10
1
88
88
84
68
79
96
66
66
59
46
40
72
52
70
60
69
b
>99
95 (71)
a
◦
Reaction condition: The dehydration reaction was first conducted in [BMIm]Cl at 130 C with 0.18 g fructose for 20 min to afford HMF. Then 35 ml water and 0.05 g catalyst
◦
were added into the reactor for hydrogenation reaction under 6 MPa H2 at 50 C for 3 h.
b
6
3% is the yield of DHMTF, and 71% is the yield of DHMF.
DHMF becomes the dominant product (69.7%) and the selectivity
of DHMTF is only 14.1% (entry 3). HMF conversion for Pt/C was
similar to Ir/C, whereas the selectivity of furan-based diols was the
lowest for Pt/C (67.8%, entry 4) among the catalysts tested. It is pos-
sibly due to the fact that Pt could catalyze both hydrogenation and
C–C scission reactions [32,33]. In addition, the relatively low hydro-
genation activity of Pt [30] increased the choice of competitive side
reactions. Exceptionally, Ni/C gave the poorest results both on HMF
conversion and the yield of diols (entry5), which possibly due to the
largest particle size of Ni/C among all the tested catalysts (see in ESI,
Fig. S1).
The irreversible CO uptake is used to calculate metal dis-
persion (ESI, Table S2). Chemisorption and reaction information
for different metal catalysts showed that the specific rate of
HMF hydrogenation catalyzed by metal catalyst was as follows:
Pd ≈ Ru > Ir > Pt > Ni. This trend is in agreement with the activity
discussed above, and is also similar to Gallezot’s report [34]. The
highest selectivity to DHMTF was obtained with Pd catalyst while Ir
catalyst preferred to C O hydrogenation to yield DHMF. Regarding
reaction, quantitative conversion with 89.3% yield of diols was
obtained, which is nearly the same as that acquired directly from
fructose (entries 1–2). As dehydration reaction of fructose losing
24.7% of HMF, it means that the impurities formed in dehydration
reaction have no clear influence on the hydrogenation reaction.
Inulin, a polymer mainly composed of fructose and a glucose chain
end, is a major component in many plants (Jerusalem artichoke,
chicory, anddahlia) [35]. When it is used as a substrate for the one-
pot transformation, hydrolysis reaction to afford hexoses was the
◦
initial step. After heating at 130 C for 20 min with 30 mg water
(1.75 mol equivs. to hexose unit), moderate HMF yield of 52.5%
was achieved (entry 3), this lower result is mainly due to the tan-
dem hydrolysis-dehydration reaction generate more by-products.
Nevertheless, the subsequent hydrogenation step proceeded effi-
ciently, exclusively afforded DHMTF with the yield of 43.1%. If
glucose and cellulose were employed as the substrates, isomer-
ization catalyst CrCl3 [36] was needed in the dehydration step to
afforded HMF yields of 42.0% and 43.6% (entries 4–5), respectively
in longer reaction time of 3 h. After hydrogenation reaction step,
the yields of furan-based diols were 35.3% and 34.0% respectively.
Thus, fructose (ketohexose) and fructose-derived polysaccharides
are superior to glucose(aldohexose) and glucose-derived polysac-
charides for DHMF and DHMTF formation under these reaction
conditions.
that reductive support TiO favors the carbonyl group hydrogenat-
2
ing (Section 3.2), we prepared TiO2 supported iridium catalyst for
fructose conversion in order to obtain high yield of DHMF. It is
interesting to find that under the same condition of Pd/C catalyzed
reaction (entry 1), Ir/TiO2 afforded 99.5% HMF conversion with
9
5.4% DHMF selectivity (the yield based on fructose was 71.2%). In
this experiment, only trace amount of DHMTF was generated (entry
). Therefore, by screening the proper metal species and support,
selective production of DHMTF (71.2% yield over Ir/TiO ) or DHMF
3
.5. Reaction pathway consideration
6
2
Besides the two major products DHMF and DHMTF, five
(
63.4% yield over Pd/C) from fructose was realized in our reaction
principal by-products were observed in most of the afore-
mentioned hydrogenation cases (Scheme 2): 5-methylfurfural
system (Table 1, entries 1 and 6).
The data in the brackets are the yields of the individual diols.
(compound 1), 5-methyl-4,5-dihydrofuran-2-carbaldehyde (com-
pound 2), 5-methyltetrahydrofuran-2-carbaldehyde (compound
3), 5-methyltetrahydrofurfuryl alcohol (compound 4), and 2,5-
dimethyltetrahydrofuran (compound 5), including some unknown
products were detected. Based on the above catalytic results and
the identified compounds (ESI, Fig. S2), a possible reaction path-
way of one-pot tandem reactions was proposed in Scheme 2: (i)
3
.4. Conversion of biomass-derived carbohydrates
Various biomass-derived carbohydrates were tested for this
transformation to afford furan-based diols. The results are shown
in Table 2. When commercial HMF was used in hydrogenation
Table 2
Production of furan-based diols from different carbohydrates.
Entry
Substrate
HMF yield/%
HMF Conv./%
Selectivity/%
DHMF
Yield of diols/%
DHMTF
Total
1
2
3
4
5
HMFa
Fructose
Inulin
Glucose
–
75
53
42
44
>99
>99
>99
>99
>99
1
4
0
3
2
89
84
82
81
76
90
88
82
84
78
90
66
43
35
34
b
c
b,d
c,d
Cellulose
a
◦
Reaction condition: 0.123 g HMF, 0.50 g [BMIm]Cl, 0.05 g 5% Pd/C, 50 C, 6 MPa H2, 3 h.
b
◦
0
.18 g hexose was heated in 0.5 g [BMIm]Cl at 130 C for 20 min, then 35 ml water and 0.05 g 5% Pd/C were added in the mixture for hydrogenation reaction under the
◦
condition of 50 C, 6 MPa H2, 3 h.
c
◦
0
6
.162 g polysaccharide was heated in 2.0 g [BMIm]Cl with the addition of 30 mg water at 130 C for 20 min, the hydrogenation step is the same as that in entry 2.
mol% CrCl3 was used in the dehydration step for 3 h.
d
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Scheme 2. Proposed reaction pathway of one-pot conversion of carbohydrates for the production of furan-based diols.
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[
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[
3
[
(
heterogeneous Pd, Pt, Ir, Ni, Ru-based catalysts catalyze HMF hydro-
[
◦
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2
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Acknowledgments
Supports from the National Natural Science Foundation of China
(
(
No.21003121, 20903089 and 21176235), 973 program of China
2009CB226102) and Dr Start-up Foundation of DICP (S201107) are
1933–1937.
gratefully acknowledged.
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Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.cattod.
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via tandem reactions, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.02.029