Tailored one-pot production of furan-based fuels from fructose in an ionic liquid biphasic solvent system

Article abstract of DOI:10.1016/S1872-2067(15)60927-5

The one-pot catalytic transformation of biomass to useful products is desirable for saving cost and time. The integration of the various reaction steps need to address the presence of incompatible reaction conditions and numerous side reactions. We report a novel process for the one-pot production of furan-based fuels, 2,5-dimethylfuran (DMF) and 2,5-dihmethyltetrahydrofuran (DMTF), from fructose by optimizing the synergic effect of an ionic liquid promoted Ru/C catalyst and the solvent effect. The dehydration of fructose and subsequent in situ hydrodeoxygenation of HMF to DMF and DMTF on Ru/C were enhanced by the use of an ionic liquid and a biphasic [BMIm]Cl/THF solvent. Elemental analysis, X-ray Photoelectron Spectroscopy, Raman spectroscopy and H₂-temperature programmed reduction-mass spectroscopy characterization showed that the ionic liquid modified the electronic density of the Ru species to favor HMF in situ hydrodeoxygenation. Moreover, THF served as a reaction-extraction solvent that extracted DMF and DMTF from the reaction layer to avoid further side reactions. A rational design that gave enhancement of the catalytic performance and product protection provides a promising strategy for the one-pot conversion of biomass to desired fuels.

Full text of DOI:10.1016/S1872-2067(15)60927-5

Chinese Journal of Catalysis 36 (2015) 1638–1646
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article (Special Issue for Excellent Research Work in Recognition of Scientists Who Are in Catalysis Field in China)
Tailored one-pot production of furan-based fuels from fructose in an
ionic liquid biphasic solvent system
a
a
a
a
a,b
a,b
a,c
Changzhi Li , Haile Cai , Bo Zhang , Weizhen Li , Guangxian Pei , Tao Dai , Aiqin Wang ,
a,c,
Tao Zhang *
a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
University of Chinese Academy of Sciences, Beijing 100049, China
Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Dalian 116023, Liaoning, China
b
c
A R T I C L E I N F O
A B S T R A C T
Article history:
The one-pot catalytic transformation of biomass to useful products is desirable for saving cost and
time. The integration of the various reaction steps need to address the presence of incompatible
reaction conditions and numerous side reactions. We report a novel process for the one-pot pro-
duction of furan-based fuels, 2,5-dimethylfuran (DMF) and 2,5-dihmethyltetrahydrofuran (DMTF),
from fructose by optimizing the synergic effect of an ionic liquid promoted Ru/C catalyst and the
solvent effect. The dehydration of fructose and subsequent in situ hydrodeoxygenation of HMF to
DMF and DMTF on Ru/C were enhanced by the use of an ionic liquid and a biphasic [BMIm]Cl/THF
solvent. Elemental analysis, X-ray Photoelectron Spectroscopy, Raman spectroscopy and
Received 29 March 2015
Accepted 3 June 2015
Published 20 September 2015
Keywords:
Biomass
Ionic liquids
H -temperature programmed reduction–mass spectroscopy characterization showed that the ionic
2
2
2
5
,5-Dimethylfuran
,5-Dimethyltetrahydrofuran
-Hydroxylmethylfufural
liquid modified the electronic density of the Ru species to favor HMF in situ hydrodeoxygenation.
Moreover, THF served as a reaction-extraction solvent that extracted DMF and DMTF from the reac-
tion layer to avoid further side reactions. A rational design that gave enhancement of the catalytic
performance and product protection provides a promising strategy for the one-pot conversion of
biomass to desired fuels.
Fructose
Biofuel
©
2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1
.
Introduction
from biomass, 2,5-dimethylfuran (DMF) and 2,5-dimethyltet-
rahydrofuran (DMTF) have received particularly attention be-
cause they are good biofuel candidates and important interme-
diates in the chemical industry. As a fuel replacement, DMF has
an ideal boiling point (92–94 °C), high energy density (30
kJ/cm ), and high research octane number (RON = 119) [5]. It
is also an intermediate for making p-xylene, one of the highest
volume bulk chemical presently derived from petroleum [6,7].
DMTF is the extensively reduced product of DMF. It has a high-
With the increasing depletion of fossil fuels and the con-
cerns over their environmental impact and greenhouse gas
effect, the development of renewable energy resources be-
comes more urgent. Biomass is the only renewable organic
carbon source in nature, which endows it with unique ad-
vantages in producing fuels and industrially important chemi-
cals [1–4]. Among the various valuable compounds derived
−3
*
Corresponding author. Tel: +86-411-84379015; Fax: +86-411-84691570; E-mail: taozhang@dicp.ac.cn
This work was supported by the National Natural Science Foundation of China (21473187, 21403213) and China Postdoctoral Science Foundation
2015M571341).
DOI: 10.1016/S1872-2067(15)60927-5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 9, September 2015
(

Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
1639
er energy content than DMF and has better stability during
OH
OH
O
O
HO
HO
O
storage because of its saturated furan ring structure [5]. DMTF
can also serve as a substitute for tetrahydrofuran (THF) in the
chemical industry [8].
In principle, DMF and DMTF can be generated from carbo-
hydrates via hydrolysis, dehydration and subsequently selec-
tive hydrogenation reactions (Scheme 1). Currently, most
studies are focused on the hydrodeoxygenation of
HO
HO
OH
OH
OH
O
HO
O
O
OH
Hydrolysis
Dehydration
- 3 H
O
DMF
HO
Glucose
H
2
O
2
HOH C
OH
2
O
OH
O
HMF
HO
O
O
O
n
HO
CH OH
2
OH OH
Fructose
OH OH
Carbohydrates
DMTF
Scheme 1. Reaction route for the conversion of biomass to furan-based
fuels DMF and DMTF.
5
1
-hydroxymethylfurfural (HMF) to produce DMF and DMTF [9,
0]. However, HMF is a versatile compound with many im-
tion step, due to the influence of unfavorable impurities, the
overall yields of DMF were only 15% and 9%, respectively, in
the above two cases.
portant applications, thus using cheap and abundant biomass
derived carbohydrate instead of the more expensive HMF as
the substrate for the production of these two products is more
cost effective and preferable.
One-pot catalysis is a powerful strategy in green chemistry.
Combining multi-step transformations in one-pot cascade ca-
talysis would provide advantages over conventional processes
with stepwise reactions, mainly by reducing the time used and
yield losses during the isolation and purification of the reaction
products. In the catalytic transformation of carbohydrates to
DMF and DMTF, due to the incompatible reaction conditions of
each step and the numerous side reactions, it is a challenge to
perform a one-pot conversion process [13]. Therefore, in the
above three examples, the isolation of the intermediate HMF
was a prerequisite for the subsequent hydrodeoxygenation
reaction.
As an example of starting from carbohydrates, Dumesic’s
group [5] pioneered a biphasic two-step process for the con-
version of fructose into DMF. In this study, fructose was first
dehydrated to HMF in an aqueous/organic system over an acid
catalyst. The purified HMF was subsequently converted to DMF
via liquid- or vapour phase hydrodeoxygenation reaction over
CuRu/C. The highest overall yield of 50% was obtained directly
from carbohydrates in a relatively complicated reaction system
with the use of a number of additives. Subsequently, Chidam-
baram et al. [11] and Binder et al. [12] used glucose and corn
stover as substrates for the production of DMF via two- or mul-
ti-step approaches. Both studies obtained fairly good yields of
the intermediate HMF. Unfortunately, in the hydrodeoxygena-
Sen et al. [14] recently provided an elegant example of the
one-pot conversion of carbohydrates to DMTF. In their experi-
Changzhi Li (Dalian Institute of Chemical Physics, Chinese Academy of Science) received Min
Enze Energy and Chemical Engineering Award in 2013, which was jointly presented by
Chinese Academy of Engineering and Sinopec Group, for his contribution in the area of "ionic
liquids mediated biomass conversion". Dr Changzhi Li received his Ph.D. degree under the su-
pervision of Prof. Zongbao (kent) Zhao, in Organic Chemistry from Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, in 2009; then he joined Prof. Tao Zhang's group where he
was promoted to an associated professor in 2012. He has published more than 20
peer-reviewed papers with over 600 citations. In 2014, he won the First Prize for Dalian Sci-
ence and Technology Innovation Award. His current research focuses on the catalytic depoly-
merization of lignin and the production of bulk and fine chemicals from renewable sources.
Tao Zhang (Dalian Institute of Chemical Physics, Chinese Academy of Science) received the
Catalysis Award for Young Scientists in 2008, which was presented by The Catalysis Society
of China. Professor Tao Zhang received his Ph.D. degree from Dalian Institute of Chemical
Physics (DICP), Chinese Academy of Sciences, in 1989, and he joined the same institute and was
promoted to full professor in 1995. He did postdoctoral research with Prof. Frank Berry at Bir-
mingham University in 1990. Prof. Zhang was an invited professor at Univesity of Poitiers
(
France) in 2006-2007, and he has been a guest professor at University of Namur (Belgium)
since 2011. He is currently the director of DICP (since 2007). Prof. Zhang has also received sev-
eral research awards, including the Distinguished Award of Chinese Academy of Sciences
(2010), Zhou Guangzhao Foundation Award for Applied Science (2009), National Award of
Technology Invention (2008, 2006, 2005). He was selected as an academician of the Chinese
Academy of Sciences. In the past decades, Prof. Zhang has successfully designed a great number
of nano and subnano metallic catalysts for applications in energy conversion and environmen-
tal control. His research interests include (1) Design and synthesis of nano- and subnano cata-
lytic materials; (2) utilization of biomass for production of chemicals.

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Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
ments, a homogeneous catalyst system composed of a soluble
Rh salt was the catalyst, and HI and chlorobenzene as additives
under a hydrogen atmosphere in water was applied. Hexose
from a wide range of biomass-derived carbohydrates were
converted into DMTF in good yields. Rauchfuss’s group [13]
also developed a formic acid participant process for the syn-
thesis of DMF from fructose whereby three steps occurred in
the one-pot, namely, dehydration of fructose to HMF, hydro-
genation HMF to bis(hydroxymethyl)-furan (BHMF), and de-
oxygenation of BHMF to DMF. While promising, too much FA
used (over 10 times molar amount than fructose) in the pro-
cess is an issue that needs to be addressed.
Ionic liquids (ILs) are currently under intensive investiga-
tion as alternative solvents for biomass conversion because
they possess tunable properties and readily dissolve biomass
resources [15–18]. In our previous study, we developed the
dehydration of carbohydrates for the production of HMF in ILs
The pressure of the column was 2.8 MPa and the column tem-
perature was 45 °C. The yield of HMF was calculated by the
equation: Yield (%) = (molar number 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 substrates)) × 100. The
selectivity of DMF or DMTF was calculated by the equation:
Selectivity (%) = (molar number of the product)  (molar
number of converted HMF) × 100. The total selectivity of fu-
ran-based fuels was calculated by the equation: Selectivity (%)
= (Selectivity of DMF) + (Selectivity of DMTF). The total yield of
furan-based diols was calculated by the equation: Total yield
(%) = (Yield of HMF) × (Conversion of HMF) × (Total selectivity
of furan-based fuels) × 100.
2.3. Characterization
[
19] and the one-pot conversion of carbohydrates to fu-
Elemental analysis (C, H, N) of the catalyst was done on a
Vario MICRO elemental analyzer. Raman spectra were meas-
ured with a Raman spectrometer (Renishaw in Via Raman Mi-
croscope) equipped with a He-Ne (514 nm) laser. A laser power
ran-based diols in a IL/water binary solvent mixture [20]. Here,
the direct production of DMF and DMTF from fructose via
one-pot tandem reaction in a biphasic IL/organic solvent sys-
tem over Ru/C was rationally designed. This ensured the cou-
pling of the relevant reactions and designed the selectivity to
DMF and DMTF. The solvent effect and the role of IL in the
transformation process were clearly explained.
of 0.1 mW was used to avoid overheating of the sample. H
2
temperature programmed reduction (TPR) was performed
using a Micromeritics Autochem 2910 (USA) equipment with 5
vol% of H
2
/N (50 mL/min) at a heating rate of 10 °C/min from
2
50 to 800 °C. The sample (50 mg) was pretreated with He flow
2
.
Experimental
.1. Materials
Fructose (99%) was purchased from Acros Organics. All the
(30 mL/min) at 120 °C for 30 min. The outlet gas was analyzed
by a TCD and mass spectroscopy (MS). X-ray photoelectron
spectroscopy (XPS, JEOL JPC-9010MC) for the Ru 3p3/2 peak
2
was obtained using Al K radiation (1486.6 eV) at 100 W and a
α
pass energy of 30 eV. Samples were fixed on a double-stick
carbon tape. The binding energies were calibrated using sput-
tered Au (4f7/2 peak at 83.8 eV).
other chemicals were obtained from local supplier and were
used as received without further purification. The Ru/C catalyst
was prepared by incipient wet impregnation followed by re-
duction in H
2
at 300 °C for 1 h. 1-Butyl-3-methylimidazolium
3. Results and discussion
chloride ([BMIm]Cl) was prepared according to our previous
study [20].
3.1. Fructose dehydration in ILs
2
.2. Conversion of fructose for the production of DMF and
A typical reaction profile in this work is a one-pot two-step
procedure, i.e., dehydration of fructose to produce HMF, cou-
pled with in situ hydrodeoxygenation of HMF to afford the tar-
get products DMF and DMTF. In the first step, the dehydration
reaction in [BMIm]Cl without the addition of catalyst at 130 °C
within 30 min afforded HMF in (78±3)% yield. Further pro-
longing the reaction time did not enhance the HMF yield, while
the color of the mixture turned dark, suggesting the formation
of black humins. As the fructose dehydration reaction in aque-
ous solution is inert when no catalyst is used [21], [BMIm]Cl
plays the role not only of the appropriate solvent but also as an
advantageous promoter for HMF production. In the following
one-pot cascade conversion of carbohydrates experiments, the
fructose dehydration reaction were all conducted at 130 °C for
30 min and then the next in situ hydrodeoxygenation step was
performed.
DHMTF
A typical process for the catalytic conversion of fructose is
as follows. 0.36 g fructose and 1.0 g [BMIm]Cl were charged
into an open autoclave and heated to 130 °C for 30 min to af-
ford HMF. About 20 mg sample was withdrawn, weighed,
quenched with cold water, and subjected to HPLC analysis to
determine the fructose conversion and HMF yield. 25 mL or-
ganic solvent and 0.1 g metal catalyst were added to the resi-
due reaction mixture. After the solution was mixed uniformly,
the hydrodeoxygenation reaction was carried out with an ini-
tial H
2
2
pressure of 5 MPa (measured at room temperature) at
20 °C for a set time. After the one-pot transformation, the re-
action solution was filtered and the clear filtrate was subject to
GC-MS analysis using the external standard method.
The HPLC analysis of the products was conducted on a Ag-
ilent 1100 equipment with a Shodex SC-101 column using extra
pure water as the mobile phase at a flow rate of 0.6 mL/min.
3.2. In situ hydrodeoxygenation: solvent effect

Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
1641
In comparison to water and common organic solvents, most
ILs including [BMIm]Cl have an undesirable high viscosity [22].
This property is especially unfavorable for mass transfer in the
gas reactions. In the HMF hydrodeoxygenation step, to alleviate
the negative effect of the high viscosity, after the dehydration
reaction, another solvent with a lower viscosity was added into
the reaction mixture for the hydrodeoxygenation reaction. As
the IL/water mixture was proved to be not a choice for the
hydrodeoxygenation of HMF [20], organic solvents with differ-
ent properties were screened to find a proper system for the
production of DMF and DMTF.
formed, the low solubility of these two products in the dipolar
IL facilitated the shift of the products to the THF layer. Accord-
ingly, ring-opening and other side reactions were avoided. In
contrast, this “solvent cage effect” and the so called “reac-
tion-extraction effect” did not exist in the binary solvent system
comprising the IL and a dipolar organic solvent, such as CH
CN,
3
i-propanol and n-butanol, because these organic solvents are
miscible with [BMIm]Cl. Besides, different solvents affect the
equilibrium constant of a reaction by different stabilization of
the reactant or product through H-bonding, dipole-dipole in-
teractions, van der Waals interactions, etc. [23].
For the in situ hydrodeoxygenation step, it was found, as
shown in Fig. 1, that HMF was completely consumed in all the
solvent mixtures within 5 h over Ru/C, while the selectivities of
the products were totally different. When dipolar organic sol-
vents were applied in the hydrodeoxygenation step, they are
miscible with [BMIm]Cl in all ratios. In this case, regardless
whether they are protic (such as i-propanol and n-butanol) or
It should be pointed out that in THF/IL, the hydrodeoxy-
genation of neat HMF afforded a lower performance (DMF and
DMTF yields of 40% and 16%, with the total yield of 56%) than
that acquired directly from fructose (Fig. 1, the two compara-
tive reactions in the THF/IL system). Noting that the dehydra-
tion reaction of fructose generated 23% byproducts, the com-
parative experiments with fructose and HMF indicated that the
impurities formed in the dehydration reaction did not have an
undesirable influence on the subsequent hydrodeoxygenation
reaction. Therefore, the removal of the impurities was not a
prerequisite in our experiment. This is an advantage over the
stepwise technology because it avoided the isolation and puri-
fication of HMF without compromising the yield of furan-based
fuels.
For the hydrotreating of biomass, the hydrogen pressure
and the reaction temperature are two crucial factors affecting
the conversion. In the THF/IL system, optimization of the reac-
tion conditions showed that the catalytic performance was only
slightly enhanced with the increasing of hydrogen pressure
(Fig. 2(a)). In contrast, it was more sensitive to the reaction
temperature (Fig. 2(b)), suggesting that hydrodeoxygenation is
a thermodynamic controlling reaction in THF/IL over the Ru/C
catalyst. These results were quite different from our previous
study where in the hydrogenation of HMF to furan-based diols,
the hydrogen pressure was the key factor that controlled the
overall rate [20].
aprotic (such as CH
CN), rather poor yields between 11%–15%
3
were obtained. The GC-MS analysis implied that severe side
reactions occurred because many byproducts such as furan
ring-opening products, carbonyl group and C=C bond hydro-
genation products as well as demethylation products and some
unknown products were detected.
It is interesting to note that THF, a weak dipolar aprotic
solvent that is immiscible with [BMIm]Cl, afforded a much
higher selectivity of furan-based fuels with a total yield of 68%
(DMF: 49% and DMTF: 19%, based on HMF). In comparison to
the above strong dipolar solvents, THF in IL greatly enhanced
the selectivity of furan-based fuels. Although a clear explana-
tion for the enhancement remains speculative, we would like to
offer some discussion. First, in the biphasic solvent system of
THF/IL, HMF was highly soluble in IL and Ru/C was also pre-
sent in the IL phase. This “solvent cage effect” [23] increased
the collision probability and thus made the catalyst more ac-
cessible to HMF. Furthermore, as soon as DMF and DMTF were
1
00
3
.3. Effect of water on the in situ hydrodeoxygenation of HMF
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
HMF conversion
DMF
DMTF
Total
It is known that in the fructose dehydration reaction, three
water molecules are released for the formation of one HMF
molecule. In the IL reaction system, once water is generated, it
is hard to separate it from the IL due to the interactions be-
tween the IL and water [24,25]. To identify the influence of
water in our system, we attempted the neat HMF hydrodeoxy-
genation reaction in THF/IL with different amounts of water. It
is interesting to find in Table 1 that in a certain range, the yield
of furan-based fuels increased with increasing water amount.
For instance, on increasing the water amount from zero to 6
mmol (one molar equivalent of IL), the total yield of the target
products increased from 56% (DMF 40%, DMTF 16%) to 67%
a
a
3
CH CN
THF
THF i-Propanol n-Butanol Toluene
Solvent
Fig. 1. Direct conversion of fructose into furan-based fuels in a binary
mixture of [BMIm]Cl/organic solvent. Reaction conditions: 0.36 g fruc-
tose was dehydrated in 1.0 g [BMIm]Cl at 130 °C for 30 min, then 25 mL
organic solvent and 0.1 g Ru/C (5 wt%) were added into the mixture
for the hydrogenolysis reaction under 5 MPa H
(DMF 47%, DMTF 20%). These results oppose the common
sense that water would induce side reactions which then de-
crease the product selectivity [26]. The following two reasons
are believed to cause this exceptional positive effect: (1) im-
provement of the mass transfer, since low viscosity water is
a.
2
at 220 °C for 5 h. Neat
HMF was used as the substrate for the hydrodeoxygenation reaction.

1642
Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
80
60
40
20
80
(
a)
(b)
DMF
DMTF
Total
70
60
DMF
DMTF
DMF+DMTF
DHMF
DHMTF
50
40
30
20
10
0
1
3
5
200
130
160
220
250
o
Hydrogen pressure (MPa)
Temperature ( C)
Fig. 2. Effects of hydrogen pressure (a) and reaction temperature (b) on the hydrodeoxygenation performance. Reaction conditions: (a) Dehydration
reaction was first conducted in 1.0 g [BMIm]Cl at 130 °C with 0.36 g fructose for 30 min, then 25 mL THF and 0.1 g 5% Ru/C were added into the
mixture for the hydrodeoxygenation reaction under H
2
atmosphere at 220 °C for 10 h; (b) The dehydration condition was the same; the hydrodeoxy-
genation reaction was carried out under 5 MPa H at different temperatures for 5 h.
2
Table 1
Effect of water amount on the production of furan-based fuels .
3
.4. The role of the IL on the in situ hydrodeoxygenation
a
reaction
H
2
O
HMF conv.
(%)
Yield (%)
Entry
(g)
DMF
40
DMTF
16
Total
56
66
67
51
It is known that the IL plays an important role in the fruc-
1
2
3
4
0
>99
>99
>99
>99
>99
tose dehydration reaction. To explore the function of the IL in
the hydrodeoxygenation step, using HMF as the substrate, we
compared the reaction with different amounts of IL under oth-
erwise identical conditions.
0.036
0.108
0.500
1.000
48
47
33
18
18
20
18
5
5
23
As shown in Table 2 (entry 1), in the absence of the IL, alt-
hough the fructose conversion was very high in the THF sol-
vent, the products only comprised 2% DMTF and a trace
amount of DMF. Instead, DHMTF, 5-methyl tetrahydrofurfuryl
a
Reaction conditions: HMF 0.252 g, THF 25 mL, 5% Ru/C 0.1 g,
BMIm]Cl 1.0 g. The hydrogenation reaction was carried out under 5
[
MPa H at 220 °C for 5 h.
2
alcohol
,2-pentanediol, 2-hexanol and pentanol were detected as the
main products in the liquid phase. In addition, gas products of
CO
, CH and C , and some insoluble humins were formed.
According to the MS data and Ref. [11], we proposed the by-
product formation pathways (Fig. 3): HMF was first saturated
(MTFA),
tetrahydrofurfuryl
alcohol
(TFA),
miscible with IL in any ratio, and (2) strong interactions such as
hydrogen bonds between water and IL suppressed water re-
lated side reactions, e.g. rehydration, hydrolysis of HMF and
intermediates [24,25,27]. It should be noted that the effect of
the IL-water interaction became weaker when much water is
present in the reaction system. This is the reason why the yield
of furan-based fuels reached a peak with the presence of 6
mmol water, and then decreased when the water amount was
higher (entry 3 versus entries 4 and 5, Table 1). Actually, we
1
2
4
H
2 6
Table 2
a
Effects of [BMIm]Cl amount on the production of furan-based fuels .
[
BMIm]Cl HMF conv.
Yield (%)
Entry
(mmol)
(%)
>99
>99
>99
>99
>99
>99
>99
>99
DMF
0
DMTF
2
1
12
20
14
1
Total
2
33
53
67
44
also tested the reaction in
a ternary solvent system
1
2
3
4
0
([BMIm]Cl/THF/H
2
O, v/v/v = 1:15:10) over Ru/C at 220 °C. No
1.15
2.87
5.73
11.46
0
32
41
47
30
66
0
DMF or DMTF was detected even on prolonging the reaction
time to 10 h. Instead, 2,5-dihydroxymethylfuran (DHMF) and
2,5-dihydroxymethyltetrahydrofuran (DHMTF) were the dom-
5
6b
7c
8d
inant products with the total yield of 88%. This result is in ac-
cordance with our previous study [20] that HMF undergoes a
hydrogenation reaction in a solvent system containing a large
amount of water. Noting that the fructose concentration was far
less than that of the IL, it can be concluded that the small
amount of water formed in the fructose dehydration step did
not cause a negative effect on the next hydrodeoxygenation
reaction. In contrast, it is an advantage of the one-pot catalytic
system over the stepwise technology since the water produced
promoted the formation of DMF and DMTF.
67
5.73
5.73
2
19
2
59
40
a
HMF 0.252 g, THF 25 mL, 5% Ru/C 0.100 g and H
2
O 0.108 g. The hy-
drodeoxygenation reaction was conducted at 220 °C under 5 MPa H for
2
5 h.
b
Catalyst was Ru/C-IL, other conditions were the same as entry 4.
c
[BMIm]Cl was replaced by NaCl, other conditions were the same as
entry 4.
d
[BMIm]Cl was replaced by 1-butyl-2,3-dimethyl-imidazolium chloride,
other conditions were the same as entry 4.

Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
1643
Fig. 3. Byproducts formation pathways for the hydrotreating of HMF with 5% Ru/C in THF without the addition of [BMIm]Cl.
in its furan ring and carbonyl group to generate DHMTF, which
was convert to MTFA via hydrodeoxygenation reaction; sub-
sequently, further hydrodeoxygenation and ring-opening reac-
tions occurred on MTFA to afford DMTF and 2-hexanol; alter-
natively, MTFA was converted to TFA, 1,2-pentanediol and
amyl alcohol via demethylation, ring-opening reaction and hy-
drodeoxygenation, respectively. Some of the above products
which anchored the IL on Ru/C.
As the IL is composed of 1-butyl-3-methylimidazolium cati-
+
–
–
on ([BMIm] ) and Cl anion, to clarify the function of Cl on the
catalyst activity, the IL was replaced by an equal molar amount
of NaCl for the HMF hydrodeoxygenation reaction under the
same condition as Table 2, entry 4. It was found that although
the conversion was still very high, the reaction only afforded
2% total yield of DMF and DMTF (Table 2, entry 7). This result
is similar to that obtained in THF without the IL (Table 2, entry
1), suggesting that NaCl has no influence on the yield of the
target products. Taken together, entries 1, 4 and 7 in Table 2
were further cracked to gases, i.e. CO
2
, CH
4
and C
2
H , etc. As
6
DMF was not detected in the reaction, it is suggested that the
furan ring in HMF was very active in THF over Ru/C.
In a parallel trial with 0.2 g [BMIm]Cl, a DMF yield of 32%
was attained (Table 2, entry 2). Clearly, the hydrogenation of
the C=C bonds in the furan ring was significantly inhibited.
Further increasing the IL amount to 0.5 and 1.0 g slightly in-
creased the yield of DMF to 41% and 47%, and the yield of
DMTF to 12% and 20%, respectively (Table 2, entries 3 and 4).
The highest total yield of 67% was obtained with 1.0 g
–
indicated that the Cl did not help convert HMF to DMF and
+
DMTF. Therefore, it was [BMIm] that played a role in the mod-
ification of Ru/C and its catalytic property.
Ru/C is a typical heterogeneous catalyst comprising Ru spe-
cies and a carbon support. With the aim to identify which com-
+
ponent interacted with [BMIm] , Raman spectroscopy, a pow-
[
BMIm]Cl. More IL did not further increase the yields of the
erful tool for carbon characterization, was performed on fresh
Ru/C and Ru/C-IL. As shown in Fig. 4, both catalysts have two
strong bands at 1401 and 1519 cm , which were assigned to
the D and G bands of the active carbon, respectively. No shift
was detected for the two bands of Ru/C-IL as compared to
target products (entry 5). We assume here that the presence of
the IL should have modified the catalyst, and changed the reac-
tion route to form DMF and DMTF. This hypothesis will be fur-
ther discussed later with the element analysis, Raman spec-
–1
troscopy, XPS and H
2
-TPR characterization, together with a
those of fresh Ru/C, and the value of I
D
/I for both catalysts was
G
series of comparison experiments.
To confirm our hypothesis, the following experiment was
designed. First, fresh Ru/C was treated in IL at 220 °C under 5
0.87. These facts indicated that the structure of the carbon
support was not changed after the treatment of the catalyst in
the IL. Thus, the high yield of the furan-based fuels can be as-
+
MPa H
2
for 2 h. This treated catalyst was then carefully washed
cribed to the interaction of [BMIm] with the metal species.
with water to ensure the removal of all the physically adsorbed
IL, and was dried under vacuum to obtain IL-treated Ru/C
Kiefer and co-workers [29] have shown that H atom on the
C position of the positively charged ring in 1,3-dialkylimidazo-
2
(
denoted as Ru/C-IL) [28]. Using this catalyst, we performed
lium-based IL is very active. It is easy to eliminate, leaving a
N-heterocyclic carbene structure on the imidazolium ring. The
HMF hydrodeoxygenation in pure THF under the same condi-
tions as Table 2, entry 1. It was interesting to find that the yield
of DMF and total yield reached 66% and 67%, respectively
1400
1200
1000
(
Table 2, entry 6). Because there was no difference in the reac-
tion conditions of the two experiments (Table 2, entries 1 and
), this result suggested that there was a modification of Ru/C
6
Ru/C-IL
8
6
4
2
00
00
00
00
0
during the treatment of the catalyst in IL, which hence changed
its catalytic activity.
The elemental analysis of Ru/C and Ru/C-IL supplied addi-
tional evidence of this. As the active carbon support was treat-
Ru/C
ed with HNO
before use, a N content of 0.92 wt% was detected
3
in fresh Ru/C. However, Ru/C-IL comprised a much higher N
content of 4.07 wt%. Since the IL contains 16 wt% of N and the
physically adsorbed IL had been removed from Ru/C by water
washing, the increased N content in Ru/C-IL should be at-
tributed to a chemical interaction between Ru/C and the IL,
2
00 400 600 800 1000 1200 1400 1600 1800
1
Raman shift (cm )
Fig. 4. Raman spectra of fresh Ru/C and Ru/C-IL.

1644
Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
presence of the carbene structure was suggested to have a re-
markable effect on metal-catalyzed reactions through coordi-
nation [30,31]. To identify whether this “carbene effect” was
present in our catalytic system, 1-butyl-2,3-dimethylimidazo-
lium chloride ([BDMIm]Cl) was prepared for the HMF hydro-
deoxygenation reaction. Unlike [BMIm]Cl, [BDMIm]Cl cannot
(1)
form a carbene structure since the C site of the imidazolium
2
ring is occupied by a methyl group. The result showed that
under the same conditions, both the ILs gave similar perfor-
mances (entry 4 versus entry 8, Table 2). This indicated that
(
2)
methylating the C
of the Ru species. Therefore, H atom on the C
2
position did not affect the catalytic activity
position of the
2
1
00 200 300 400 500 600 700 800
imidazolium ring is not the reason for the high yield of fu-
ran-based fuels.
o
Temperature ( C)
Fig. 6. H -TPR profiles of Ru/C (1) and Ru/C-IL (2).
2
The ligand effect is the use of a ligand to alter the electronic
properties of the active metal by electron transfer from the
ligand to the metal species [32]. This “ligand (or electronic)
effect” significantly affects the catalytic activity and selectivity
in various chemical reactions [33]. An obvious feature of the
the Ru electron properties. Fig. 6 summarizes the TPR profiles
of fresh Ru/C and Ru/C-IL. In the low temperature region of
140 °C, only one peak was detected for both catalysts, which
1,3-dialkylimidazolium cation is that one of the N atoms in the
was ascribed to the reduction of RuO . The hydrogen consump-
2
imidazolium ring contains a lone pair electron [34]. This N at-
om can act as a ligand to coordinate with the Ru species and
thus modify the electronic property of the actives site. XPS
characterization of the catalyst demonstrated the “ligand ef-
fect” of the IL on the Ru species. In the XPS measurement, since
the Ru 3d5/2 peak overlapped with that of C 1s [35], the binding
energy of the Ru 3p3/2 orbital was measured. As shown in Fig.
tion signals at 270 °C and 510 °C were accompanied by the
formation of methane (confirmed by MS analysis), suggesting
that some carbon species were reduced to methane. In the TPR
profile of Ru/C-IL, it is interesting that the peak at 270 °C was
much larger than that of Ru/C. Obviously, after treating with
the IL, the Ru species was greatly changed in property, which
probably led to some methanation of the support. These
changes to the Ru species are believed to be responsible for the
much improved hydrodeoxygenation performance.
5(a), the binding energy of Ru/C-IL was 0.4 eV lower than that
of fresh Ru/C (463.5 eV), indicating that the electron cloud
density of the Ru species was increased after treating with the
IL. Due to the conjugative effect of the imidazolium ring, the N
4. Conclusions
1s of [BMIm]Cl in C-IL (IL treated carbon) [28] only exhibited
one peak (401.6 eV, Fig. 5(b)). However, it was interesting to
find that two N 1s peaks of 399.8 and 401.2 eV appeared in the
Ru/C-IL sample (Fig. 5(b)), suggesting that one N atom was
coordinated with the Ru species, resulting in the different
binding energy for the two N atoms in the imidazolium ring of
We achieved the direct production of furan-based fuels,
DMF and DMTF, from fructose via one-pot tandem reactions.
The nature of the organic solvent in the IL containing binary
solvent mixture and the water amount strongly affected the
reaction. Characterization of the catalysts and the parallel ex-
periments indicated that the interaction between the cations of
the IL and Ru species changed the charge density of the metal
[BMIM]Cl.
H
2
-TPR measurement further confirmed the modification of
(a)
(b)
463.1
401.2
399.8
Ru/C-IL
Ru/C-IL
C-IL
401.6
463.5
Ru/C
4
90
480
Binding energy (eV)
Fig. 5. XPS spectra of Ru/C, Ru/C-IL and C-IL. (a) Ru 3p3/2; (b) N 1s.
470
460
450
Binding energy (eV)

Changzhi Li et al. / Chinese Journal of Catalysis 36 (2015) 1638–1646
1645
Graphical Abstract
Chin. J. Catal., 2015, 36: 1638–1646 doi: 10.1016/S1872-2067(15)60927-5
Tailored one-pot production of furan-based fuels from fructose in
an ionic liquid biphasic solvent system
Changzhi Li, Haile Cai, Bo Zhang, Weizhen Li, Guangxian Pei, Tao Dai,
Aiqin Wang, Tao Zhang *
One-pot
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences;
Collaborative Innovation Center of Chemistry for Energy Materials (iChEM)
Ru/C
BMIm]Cl-THF
[
Fructose
One-pot production of 2, 5-dimethylfuran and 2, 5-dihmethyltetrahydro-
furan from fructose by optimizing the synergic effect of ionic liquid pro-
moted Ru/C catalyst and solvent effect was reported.
species, which is the reason for the high selectivity of the fu-
ran-based fuels. The advantages of the IL in the fructose dehy-
dration reaction, its role in the modification of the Ru species,
as well as the biphasic [BMIm]Cl/THF solvent system together
gave the high yield of furan-based fuels. This catalytic system
featured a simple process with no need for intermediate sepa-
ration processes and it gave a high performance, which brings
this technology nearer to the cost-efficient production of biofu-
els from biomass.
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