Hydrogenolysis of glycerol catalyzed by Ru-Cu bimetallic catalysts supported on clay with the aid of ionic liquids

Article abstract of DOI:10.1039/b901425j

Glycerol is a well-known renewable chemical, and its effective transformation to valuable chemicals accords well with the principles of green chemistry. In this work, a series of Ru-Cu bimetallic catalysts were prepared using cheap and abundant clay, bentonite, as the support. Bentonite was modified with a functional ionic liquid 1,1,3,3-tetramethylguanidinium lactate (TMGL) in an attempt to develop highly efficient catalysts. Hydrogenolysis of aqueous solution of glycerol was performed with the immobilized Ru-Cu catalyst under temperatures of 190-240°C and pressures of 2.5-10 MPa. The bimetallic catalysts were very efficient for promoting the hydrogenolysis of glycerol. 100% of glycerol conversion and 85% yield of 1,2-propanediol could be achieved at 230°C and 8 MPa. The conversion of glycerol and the selectivity to 1,2-propanediol did not decrease after the catalyst was used 5 times. TMGL played a crucial role in fabricating the new catalysts. The catalysts were characterized by FT-IR, XPS, SEM and TEM, and the reasons for the excellent performances of the catalyst were also discussed.

Full text of DOI:10.1039/b901425j

View Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/greenchem | Green Chemistry
Hydrogenolysis of glycerol catalyzed by Ru-Cu bimetallic catalysts
supported on clay with the aid of ionic liquids
Tao Jiang,* Yinxi Zhou, Shuguang Liang, Huizhen Liu and Buxing Han*
Received 22nd January 2009, Accepted 25th March 2009
First published as an Advance Article on the web 9th April 2009
DOI: 10.1039/b901425j
Glycerol is a well-known renewable chemical, and its effective transformation to valuable
chemicals accords well with the principles of green chemistry. In this work, a series of Ru-Cu
bimetallic catalysts were prepared using cheap and abundant clay, bentonite, as the support.
Bentonite was modified with a functional ionic liquid 1,1,3,3-tetramethylguanidinium lactate
(
TMGL) in an attempt to develop highly efficient catalysts. Hydrogenolysis of aqueous solution of
◦
glycerol was performed with the immobilized Ru-Cu catalyst under temperatures of 190–240 C
and pressures of 2.5–10 MPa. The bimetallic catalysts were very efficient for promoting the
hydrogenolysis of glycerol. 100% of glycerol conversion and 85% yield of 1,2-propanediol could be
◦
achieved at 230 C and 8 MPa. The conversion of glycerol and the selectivity to 1,2-propanediol
did not decrease after the catalyst was used 5 times. TMGL played a crucial role in fabricating the
new catalysts. The catalysts were characterized by FT-IR, XPS, SEM and TEM, and the reasons
for the excellent performances of the catalyst were also discussed.
Introduction
produced through petroleum routes, such as the ethylene
12
oxide route (Shell technology) or acrolein (Degussa-DuPont
With the gradual depletion of fossil resources, an urgent task is
to replace fossil resources with renewable materials. Commodity
chemicals that are currently used to produce pharmaceuticals,
plastics and transportation fuels are expected to be produced
from renewable materials in future. This strategy is especially
crucial for the sustainable development of the society and
economy. Much effort, therefore, has been devoted to the con-
version and utilization of renewable feedstocks and chemicals
in recent years. Glycerol is one of the top-12 building block
chemicals identified by the U.S. Department of Energy. As a
biomass-derivate, glycerol can be commercially produced by the
microbial fermentation of sugars such as glucose and fructose.
In addition, glycerol is a byproduct in a large amount from
the production of biodiesel by transesterification of plant and
animal oils with methanol. 10 wt% of glycerol is produced in
manufacturing biodiesel fuel. It is no doubt that development of
chemical processes to convert low-cost glycerol to more valuable
chemicals is of great importance. Recently, several excellent
papers have given overviews on the recent development in the
13
technology) for the production of 1,3-propanediol (1,3-PDO)
and the hydrolysis of propylene oxide with water for manu-
facturing 1,2-propanediol (1,2-PDO). 1,3-PDO is mainly used
as a starting material for producing polymers and 1,2-PDO
is often used directly as intermediates or additives to produce
9,14
antifreezing agent, lubricants, foods, cosmetics, and resins.
Increasing attention has consequently been paid to the hydro-
genolysis of glycerol to produce 1,3-PDO and 1,2-PDO, and
about 10 papers were published in 2008. Solid catalysts have
exhibited unique advantages in separation and recovery of
catalysts. Metals including Cu, Ni, Pd, Pt, Ru, Rh, Cr, and
Au have been extensively used as the active components for
hydrogenolysis of glycerol, and the reactions were conducted at
1,2
3
4–6
temperatures of 453–513 K and hydrogen pressures of around
7
15–22
6–10 MPa.
Among the metals used, ruthenium has shown a high activity
23–26
for the hydrogenolysis of glycerol,
often unavoidable
but C–C bond cleavage is
27,28
resulting in the high yields to products of
small molecules, including methane, methanol, CO, and CO ,
2
8–11
conversion of glycerol into value-added chemicals.
etc. The work by Davis et al. indicated that Ru favored the
It is known that glycerol can be catalytically converted
into functionalized and value-added chemicals via a variety
of reaction routes, such as oxidation, hydrogenolysis, dehydra-
tion, pyrolysis, steam reforming, etherification, esterification,
oligomerization and polymerization, etc. The hydrogenolysis
of glycerol produces oxygenated chemicals including ethylene
glycol (EG) and propylene glycol. Propylene glycol is presently
formation of EG over 1,2-PDO. C–C bond cleavage is thought to
29,30
occur primarily via a metal-catalyzed reaction route over Ru.
16
Montassier et al. carried out the hydrogenolysis of glycerol
under 30 MPa H at 533 K. Mainly methane was obtained
2
in the presence of RANEYꢀR Ni, Ru, Rh and Ir catalysts,
while 1,2-PDO was the main product when RANEYꢀR Cu was
used as a catalyst. Cu also exhibited good performance for the
31,32
hydrogenolysis of glycerol in other works.
Chaminand et al.
reported the hydrogenolysis of glycerol over CuO/ZnO catalysts.
At 180 C and 80 bar hydrogen pressure 100% selectivity to
Beijing National Laboratory for Molecular Sciences (BNLMS), Centre
for Molecular Science, Institute of Chemistry, Chinese Academy of
Sciences, Beijing, 100190, China. E-mail: Jiangt@iccas.ac.cn,
Hanbx@iccas.ac.cn; Fax: +86 10 62562821; Tel: +86 10 62562821
◦
1
,2-PDO can be obtained in water when the conversion of
23
glycerol was 19%. More recently, Xia and coworkers prepared
1
000 | Green Chem., 2009, 11, 1000–1006
This journal is © The Royal Society of Chemistry 2009

View Online
highly dispersed copper nanoparticles supported on silica by
the precipitation–gel technique, which showed 94.3% selectivity
toward 1,2-PDO with 73.4% glycerol conversion at 473 K and a
total pressure of 9 MPa.
Recently, the preparation of catalysts assisted by ionic liquids
produced by Beijing Chemical Reagents Company. All chemicals
were used as received.
33
Catalyst preparation
In this work, bentonite was modified with ionic liquid 1,1,3,3-
tetramethylguanidinium lactate (TMGL), which was prepared
directly by neutralization of 1,1,3,3-tetramethylguanidine with
3
4
(
ILs) has attracted much attention. For example, Mehnert et al.
dispersed 1-butyl-3-methylimidazolium hexafluorophosphate
[bmim][PF ]) and 1-butyl-3-methylimidazolium tetrafluorobo-
rate ([bmim][BF ]) on silica gel to provide a solvent environ-
ment for the Rh complex. The as-prepared catalyst showed
(
6
43
lactic acid at room temperature (Scheme 1). Before being
used as the supports, bentonite was treated with TMGL to
exchange the Na cations with the IL cations. The molar ratio
of IL to the CEC of bentonite was 1.2:1. Bentonite was first
dispersed in an aqueous solution of TMGL and stirred for 6 h
at room temperature. After being separated from the solution
by filtration, bentonite was treated for the second time with the
same procedures. Then bentonite was washed three times with
4
35
excellent catalytic activity and stability for hydrogenation.
More interestingly, some functional ILs exhibit a strong ability
to stabilize nanoparticles. Different Pd or Ru nanoparticle
catalysts have been prepared with the assistance of guanidinium-
based IL, which also showed outstanding catalytic performance
36,37
for the hydrogenation of benzene and olefins.
More recently,
◦
deionized water, and dried at 120 C overnight, which was labeled
a series of very effective supported catalysts for different organic
reactions have been prepared using different ILs and solid
as TMG-BEN.
38–40
supports.
Natural clay minerals are a type of environmentally benign
material. Bentonite (BEN) is a clay consisting predominantly of
montmorillonite. It has a layered structure, large surface areas,
and cation exchange capacity. The special properties of bentonite
make it a valuable material for a wide range of applications, such
as pharmaceuticals, cosmetics, environment, agriculture, and
catalysis, etc. Bentonite is potentially a good catalyst support.
For example, an excellent catalyst has been prepared using ion-
Scheme 1 The synthesis of TMGL.
The Ru or Cu catalysts supported on TMG-BEN were
prepared by the following procedures: 1 g of TMG-BEN was
dispersed in an aqueous solution of RuCl
.297 mmol Ru; 20 mL of deionized water) or Cu(NO
0.0717 g, 0.297 mmol Cu; 20 mL of deionized water), and the
3
·3H
2
O (0.0776 g,
41
exchanged montmorillonite for the hydrogenation of benzene.
A montmorillonite-enwrapped scandium has been used as a
0
(
3
)
2
·3H
2
O
42
heterogeneous catalyst for the Michael reaction.
mixture was stirred for 2 h at room temperature. Then water was
As discussed above, both Ru and Cu can catalyze the reaction,
with certain advantages. A combination of them may produce
a more efficient catalyst. In this work, a series of Ru-Cu
bimetallic catalysts were prepared using bentonite as the support
with the aid of 1,1,3,3-tetramethylguanidinium lactate (TMGL).
Hydrogenolysis of glycerol was performed with the immobilized
Ru-Cu catalyst (designated as Ru-Cu/TMG-BEN). The results
demonstrated that the catalyst was highly active and selective
for the hydrogenolysis of glycerol to produce 1,2-PDO. The IL
played a crucial role in fabricating the new catalysts. As far as
we know, this is the first work on the hydrogenolysis of glycerol
carried out using Ru-Cu bimetallic catalysts.
removed under vacuum. The obtained catalyst was reduced in a
◦
flow of pure H
2
at 220 C for 3 h. The as-obtained catalyst was
designated as Ru/TMG-BEN and Cu/TMG-BEN, respectively.
The Ru-Cu bimetallic catalysts supported on TMG-BEN
were prepared by the following procedures: 1 g of the modified
bentonite was added to the aqueous solution of RuCl
0.0776 g, 0.297 mmol Ru; 20 mL of deionized water), and the
mixture was stirred for 2 h at room temperature. Then NaBH
3
·3H
2
O
(
4
was used to reduce Ru. The solid was washed with deionized
◦
water and dried at 100 C. Then the supported Ru catalyst was
added to the aqueous solution of Cu(NO
.1 mmol Cu; 20 mL of deionized water), and the mixture was
stirred for 2 h at room temperature. After being reduced with
3
)
2
·3H
2
O (0.0239 g,
0
NaBH
4
the solid was washed with deionized water and dried at
at
Experimental
◦
1
00 C. Finally, the solid was reduced in a flow of pure H
2
◦
◦
Materials
220 C for 3 h and then 300 C for 3 h. The as-made catalysts
were labeled as Ru-Cu/TMG-BEN. The content of Ru in this
catalyst was 3 wt% of the support and the molar ratio of Ru
to Cu was 3/1. The catalysts with other Ru/Cu ratios were
prepared using the same procedures. For comparison, the Ru-
Cu bimetallic catalyst supported on unmodified bentonite was
also prepared using a similar method, which was referred to as
Ru-Cu/BEN.
The clay mineral used in this work is a smectite rich white
bentonite provided by Zhejiang Sanding Scientific and Tech-
nology Co., Ltd., China. The composition of the clay was
5
K
0
8.98% SiO
O, 0.87% CaO, 1.31% Fe
.08% FeO. It was microporous and cation-rich. The cation
exchange capacity (CEC) of the bentonite was 99 mmol/100 g.
was purchased from Beijing Analytical Instrument Factory
2
, 19.82% Al
2
O
3
, 3.73% MgO, 5.18% Na
2
O, 0.42%
2
2
O
3
, 0.10% TiO , 0.74% P
2
2
O
5
, and
H
2
Catalyst characterization
with a purity of 99.99%. Glycerol, 1,2-propanediol, ethy-
lene glycol, n-butanol, and N,N-dimethylformamide (DMF)
were purchased from Sinopharm Chemical Reagent Co., Ltd.
Fourier transform infrared spectroscopy (FT-IR) spectra were
determined using a Bruker Tensor 27 spectrometer, and
the samples were prepared by the KBr pellet method. The
NaBH
4
, Cu(NO
3
)
2
·3H
2
O, and RuCl
3
·3H
2
O were A.R. grade and
This journal is © The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 1000–1006 | 1001

View Online
◦
morphology of the catalysts was observed with a transmission
electron microscope (TEM, Tecnai 20, Philips). The X-ray
photoelectron spectrum (XPS) data of the as-prepared samples
were obtained with an ESCALab220i-XL electron spectrometer
from VG Scientific using 300 W MgKa radiation. The base
pressure was about 3 ¥ 10 mbar. The binding energies were
referenced to the C 1 s line at 284.8 eV from adventitious carbon.
X-ray Diffraction (XRD) was performed on a X’PERT SW
X-ray diffractometer operated at 30 kV and 100 mA with CuKa
radiation. Scanning electron microscope (SEM) examination
was carried out on a scanning electron microscope (JEOL, JSM-
Then the catalyst was dried at 60 C under vacuum for 3 h
◦
and 100 C for 2 h in air. The catalyst was reused in the
next run directly. Reaction conditions were as follows: catalyst,
Ru-Cu/TMG-BEN (Ru 3 wt%, Ru/Cu 3/1); catalyst amount,
0.3 mol% Ru/glycerol; reaction temperature, 225 C; reaction
time, 20 h; glycerol, 5 mmol (0.46 g); water, 1.0 mL; initial
pressure, 10.0 MPa.
◦
-
9
Results and discussion
In the experiments, 1,2-PDO, 1,3-PDO, ethylene glycol (EG),
-propanol (1-PO), 2-propanol (2-PO), C
were detected in the liquid products. CH and CO
4
300) operated in a high-vacuum mode at 15 kV, which provided
1
2
H
5
OH, and CH
3
OH
general textural information of the samples. Thermogravimetric
analysis of TMG-BEN was performed on a TGA Q50 V20.7
Build 32 thermogravimetric analysis system in the atmosphere
4
2
were observed
in the gas products. Conversion of glycerol is defined as the
ratio of number of moles of glycerol consumed in the reaction
to the total moles of glycerol initially added. Selectivity to
liquid product is defined as the ratio of number of moles of
glycerol consumed to produce liquid product to the number of
moles of converted glycerol. Composition of liquid product was
calculated based on C-based moles of each component in the
liquid product.
◦
at a heating rate of 20 C per min.
Catalytic activity measurement
The hydrogenolysis of glycerol was carried out in a 7 mL
autoclave reactor under stirring. Typically, the reactor was
charged with glycerol (5 mmol, 0.46 g) and the catalyst (0.084 g,
0
.3 mol% of Ru/glycerol) in 1.0 mL deionized water, and purged
with 2.0 MPa hydrogen three times before the reaction. An air
bath was used to heat the reactor and its temperature was con-
trolled by a PID temperature controller (model SX/A-1, Beijing
Tianchen Electronic Company). The temperature fluctuation
Effect of Ru/Cu molar ratio
A series of Ru/Cu bimetallic catalysts were prepared using
TMGL modified BEN as the support by changing the molar
ratio of Ru and Cu. In all of the catalysts, the content of Ru was
◦
of the constant temperature air bath was ±0.1 C. After the
3
wt% of the support. Table 1 summarized the results of these
autoclave was heated to the reaction temperature, hydrogen was
charged up to the desired pressure. After a required period, the
autoclave was cooled and the gases were released and collected.
The liquid products were analyzed using a GC (Agilent 6820)
equipped with a PEG-20M (30 m) capillary column and a FID
detector. n-Butanol was employed as the internal standard to
calculate the product compositions and DMF was used as the
solvent. The gas product was analyzed using a GC (Agilent
catalysts in catalyzing the hydrogenolysis of aqueous glycerol.
When Ru/TMG-BEN catalyst was used (Table 1, Entry 1), the
conversion of glycerol could reach 90.7%. But obvious cleavage
of C–C bonds was observed and the selectivity to liquid product
was only 27.4%. A large amount of gas product (CH
CO ) was detected. This is consistent with the results of other
researchers.
4
and
2
16,29,30
In addition, the content of EG in the liquid
product was more than 30%, which is also high compared with
the results using other catalysts in Table 1. EG is formed via
the cleavage of the C–C bond, further demonstrating that Ru is
active for cleavage of the C–C bond. On the contrary, Cu/TMG-
BEN exhibited low conversion of glycerol (26.5%), but high se-
lectivity to liquid product, especially 1,2-PDO (Table 1, Entry 8),
indicating Cu catalysts have poor activity towards C–C bond
4
890) equipped with a packed carbon molecular sieve column
(
2 m long, 3 mm o.d.) and a TCD detector.
Recycling procedure of Ru-Cu/TMG-BEN
In the recycling experiment, the catalyst was separated by
centrifugation and washed with deionized water three times.
Table 1 Effect of molar ratio of Ru/Cu on the catalytic performance of Ru-Cu/TMG-BEN in the hydrogenolysis of glycerol
C-based composition of
liquid products/mol%
a
Entry
Molar ratio of Ru/Cu
Conversion of glycerol/%
Selectivity to liquid product/%
1,2-PDO
EG
Others
1
2
3
4
5
6
7
8
3/0
3/0.5
3/1
3/2
3/3
3/4
3/9
0/3
90.7
71.9
70.9
66.1
64.4
41.7
27.0
26.5
27.4
34.4
46.1
40.4
30.6
23.4
22.0
59.1
62.3
57.6
71.7
70.3
69.5
72.7
79.4
83.1
32.7
37.3
23.6
24.8
28.6
23.7
17.9
11.6
5.0
5.1
4.7
4.9
1.9
3.6
2.7
5.3
◦
Reaction conditions: catalyst, Ru-Cu/TMG-BEN (Ru 3 wt%); temperature, 195 C; reaction time, 18 h; catalyst amount, 0.6 mol% Ru/glycerol;
◦
a
glycerol, 5 mmol (0.46 g); water, 1.0 mL; Initial pressure at 195 C, 10.0 MPa. Including 1-propanol (1-PO), 2-propanol (2-PO), C
CH OH.
2 5
H OH, and
3
1
002 | Green Chem., 2009, 11, 1000–1006
This journal is © The Royal Society of Chemistry 2009

View Online
2
Table 2 Effect of H pressure on the performance of Ru-Cu/TMG-BEN
C-based composition of
liquid products/mol%
◦
a
T/ C
P/MPa
Conversion of glycerol/%
Selectivity to liquid product/%
1,2-PDO
EG
Others
2
10
10
8
6
71.4
71.5
77.4
87.6
81.6
100.0
100.0
100.0
65.0
67.0
66.3
67.0
31.3
98.5
99.5
79.1
83.3
85.7
84.6
84.5
87.3
86.4
85.4
83.4
14.7
12.3
12.9
13.5
7.3
9.4
7.6
2.0
2.0
2.5
2.0
5.4
4.2
7.0
13.3
5
2
.5
2
30
10
8
6
3.3
Reaction conditions: catalyst, Ru-Cu/TMG-BEN (Ru 3 wt%, Ru/Cu 3/1); reaction time, 18 h; catalyst amount, 0.3 mol% Ru/glycerol; glycerol,
a
5
2 5 3
mmol (0.46 g); water, 1.0 mL. Including 1-propanol (1-PO), 2-propanol (2-PO), C H OH, and CH OH.
cleavage and good activity towards C–O bond hydrogenation.
The results in Table 1 indicate that addition of Cu to Ru/TMG-
BEN could restrain the catalyst from catalyzing the cleavage of
the C–C bond and increase the selectivity to 1,2-PDO and other
liquid products. With the decreased molar ratio of Ru to Cu, the
conversion of glycerol gradually decreased and there were max-
ima in both of the selectivity to liquid product and the content of
selectivity to liquid product also approached 100% under 8 MPa
and 10 MPa, and the content of 1,2-PDO was 86%. Therefore,
the yield of 1,2-PDO could be as high as 85.1% at the optimized
reaction conditions.
Table 3 presents the results at 10 MPa and different tempera-
tures. The conversion of glycerol increased with the rising tem-
◦
◦
perature and reached 100% at 230 C and 240 C. The selectivity
to liquid product also increased with increasing temperature.
The content of 1,2-PDO in the liquid product reached a maxi-
1
,2-PDO in the liquid product (Table 1, Entries 2–7). When the
molar ratio of Ru/Cu was 3/1, Ru-Cu/TMG-BEN exhibited
the best performance (Table 1, Entry 3).
◦
◦
mum at 230 C. At 240 C, the content of 1,2-PDO in the liquid
product decreased to 76.1%, indicating that high temperature
promoted the formation of small molecular products.
Effect of reaction conditions
In order to investigate the effect of TMG on the properties
of the as-prepared catalyst, the reaction was conducted using
Ru-Cu/TMG-BEN and Ru-Cu/BEN at the same reaction con-
ditions. As shown in Table 3, when the reaction was conducted
for 18 h, the conversion of glycerol over the two catalysts was
all 100% (Table 3, Entry 5 and Entry 8), and the content of
1,2-PDO in the liquid product was similar. The selectivity to
liquid product over Ru-Cu/TMG-BEN was 98.5%, which was
much higher than 78.1% catalyzed by Ru-Cu/BEN. When the
reaction was conducted for a short time of 10 h, the conversion
of glycerol over the two catalysts was all less than 100% (Table 3,
Entry 6 and Entry 9). Although the content of 1,2-PDO in
In this work, the effects of reaction temperature, reaction time
and H pressure on the reaction were investigated systematically
2
using the catalyst Ru-Cu/TMG-BEN with Ru/Cu molar ratio
of 3/1 because it was the best catalyst, as can be seen from
Table 1.
◦
◦
The effect of pressure was studied at 210 C and 230 C, and
the results are given in Table 2. The data in the table indicate that
the pressure did not affect the content of 1,2-PDO in the liquid
◦
product considerably. At 210 C, the selectivity to liquid product
◦
was low when the pressure was low (2.5 MPa). At 230 C, glycerol
could be converted completely at the pressures studied. The
Table 3 Effect of reaction temperature on the performance of Ru-Cu/TMG-BEN
C-based composition of liquid
products/mol%
◦
a
Entry
T/ C
Glycerol conversion/%
Selectivity to liquid product/%
1,2-PDO
EG
Others
1
2
3
4
5
6
7
8
9
190
200
210
220
230b
230
240
48.8
59.2
71.4
90.0
100.0
86.9
100.0
100.0
80.1
34.0
59.6
65.0
75.7
98.5
97.3
98.9
78.1
72.1
60.7
74.3
83.3
84.4
86.4
87.1
76.1
87.1
85.9
32.9
22.1
14.7
13.1
9.4
9.8
9.3
6.4
3.6
2.0
2.5
4.2
3.1
14.6
3.4
2.9
c
230
9.5
11.2
d
230
Reaction conditions: catalyst, Ru-Cu/TMG-BEN (Ru 3 wt%, Ru/Cu 3/1); catalyst amount, 0.3 mol% Ru/glycerol; reaction time, 18 h; glycerol,
a
b
5
1
mmol (0.46 g); water, 1.0 mL; initial pressure, 10.0 MPa. Including 1-propanol (1-PO), 2-propanol (2-PO), C
2
H
5
OH, and CH
3
OH. Reaction time,
c
d
0 h. Conducted using the catalyst unmodified with IL, Ru-Cu/BEN (Ru 3 wt%, Ru/Cu 3/1); reaction conditions were the same. Conducted with
Ru-Cu/BEN (Ru 3 wt%, Ru/Cu 3/1); reaction time, 10 h.
This journal is © The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 1000–1006 | 1003

View Online
the liquid product over the two catalysts were similar, Ru-Cu/
TMG-BEN showed higher activity and higher selectivity to
liquid product than Ru-Cu/BEN. Therefore, Ru-Cu/TMG-
BEN exhibited better performance than Ru-Cu/BEN.
of Ru-Cu/TMG-BEN is that the particle size was unchanged in
the reaction process, while the metal particles in Ru-Cu/BEN
became larger and larger during the reaction, and therefore, the
performance of the catalyst was relatively poor. This indicates
that TMG played an important role in dispersing and stabilizing
the metallic particles in the catalyst because the only difference
of the two catalysts was that ionic liquid TMGL was utilized
when preparing Ru-Cu/TMG-BEN.
Catalyst characterization
Some typical catalysts were characterized by XPS. Fig. 1 dis-
plays the XPS spectra of Ru/TMG-BEN, Cu/TMG-BEN, and
Ru-Cu/TMG-BEN (Ru/Cu, 3/1 in moles). The binding en-
ergy of Ru in Ru/TMG-BEN can be observed at 280.4 eV
Bentonite has a layered structure and negative charge in the
silicate layers. On the basis of these special characteristics, it can
exchange cations with IL or other reagents to compensate the
negative charge. There are successful examples which demon-
strate that the interactions between nanoparticles and polymers
or surfactants can be used to intercalate nanoparticles into
the interlayer spaces of montmorillonite. For example, D e´ k a´ ny
et al. proved rhodium particles can be stabilized by polymers
(
Ru3d5, Fig. 1a), and the binding energy of Cu in Cu/TMG-
BEN is 933.3 eV (Cu2p3, Fig. 1b). In catalyst Ru-Cu/
TMG-BEN, the binding energy of Ru is shifted to 280.6 eV, and
that of Cu to 934.0 eV. Therefore, there existed strong interaction
between Ru and Cu and some electrons might be transferred
from Ru to Cu in the Ru-Cu catalysts.
44
and by the lamellae of layered silicates of montmorillonite.
Kir a´ ly et al. prepared ultrafine Palladium particles on ationic
The morphology and microstructure of the support and
catalysts were studied by SEM and TEM. Fig. 2 shows the
SEM images of the pristine bentonite (a) and Ru-Cu/TMG-
BEN (b). Clearly, the morphology of Ru-Cu/TMG-BEN was
similar to that of bentonite. The TEM images of Ru-Cu/TMG-
BEN and Ru-Cu/BEN are also shown in Fig. 2. In catalyst
Ru-Cu/TMG-BEN, the diameters of the metal particles were in
the range of 5–8 nm (Fig. 2c), and the particle size in Ru-Cu/
BEN was similar (Fig. 2e). However, after these two catalysts
were used separately once, the size of the nanoparticles on the
surface of the two catalysts was quite different. For the former,
most nanoparticles were still in the range of 5–8 nm (Fig. 2d).
The metal particles in catalyst Ru-Cu/BEN aggregated and the
size of the nanoparticles increased to about 50 nm (Fig. 2f). It
can be deduced that the main reason for the better performance
45
and nionic clays, mediated by oppositely charged surfactants.
In the as-prepared catalyst, TMG ions were fixed on the
surface or interlayer of bentonite by electrostatic force after ion-
exchange. On the other hand, TMG cations have the ability to
stabilize nanoparticles, which stems from their electron-donor
46,47
36–38
properties
and has been demonstrated in other work.
The metal particles combined with TMG ions on the surface
of the bentonite with the assistance of coordination interaction.
In this way, the nanoparticles were supported on the surface
or interlayer of bentonite by combination of coordination
and electrostatic force. The coordination interaction existed
between metallic particles and TMG, and the electrostatic
force between TMG and bentonite. Both the electrostatic and
coordination forces are very strong, which prohibit aggregation
Fig. 1 XPS spectra of catalyst: (a) Ru/TMG-BEN, (b) Cu/TMG-BEN, (c) and (d) Ru-Cu/TMG-BEN (Ru/Cu, 3/1 in moles).
004 | Green Chem., 2009, 11, 1000–1006
1
This journal is © The Royal Society of Chemistry 2009

View Online
Fig. 2 SEM images of (a) pristine bentonite; (b) Ru-Cu/TMG-BEN; (c) TEM images of fresh catalyst A (Ru-Cu/TMG-BEN); (d) Catalyst A after
one run; (e) fresh catalyst B (Ru-Cu/BEN); and (f) catalyst B after one run.
of the nanoparticles effectively. Therefore, the catalyst was stable
during the reaction. After reaction, the organic products were
collected and analyzed by AAS (atomic absorption spectrum)
analysis for Ru and Cu metals, and metal leaching was not
detected. Results of recyclability of Ru-Cu/TMG-BEN also
supported this from another aspect. It can be seen from Fig. 3
that the activity and selectivity of the catalyst did not change
after recycling 4 times.
Fig. 4 FT-IR spectra of the pristine bentonite and the as-prepared
catalysts: a) the pristine bentonite, b) TMG-bentonite, c) fresh catalyst
A (Ru-Cu/TMG-bentonite), and d) catalyst A after one run.
-
1
-1
The specific peaks of CH
2
3
group at 1414 cm , 1463 cm , and
-
1
-1
967 cm , and the peak of C=N bond at 1640 cm can be ob-
served in the spectrum of Ru-Cu/TMG-BEN which accord well
with the FT-IR spectrum of TMG-BEN (Fig. 4). In addition,
Fig. 4d shows the FT-IR spectrum of Ru-Cu/TMG-BEN after
Fig. 3 Results of the recycle of catalyst Ru-Cu/TMG-BEN.
one run. The specific peaks of the CH
3
group and C=N bond
Glycerol conversion;
Selectivity to liquid product;
1,2-PDO
can also be observed clearly, indicating that TMG cations still
existed on the surface of bentonite after the reaction. Therefore
the metal particles in Ru-Cu/TMG-BEN did not aggregate.
content in liquid product.
Some characterizations were conducted to confirm the ex-
istence of TMG cations on the surface of the catalyst. The
presence of the cation of the ionic liquid TMGL in this catalyst
was supported by the fact that the catalyst contained 10 wt%
organic compound, as determined by TGA. The existence of the
TMG cations was also supported by the FT-IR spectra (Fig. 4).
Conclusions
In conclusion, the Ru-Cu bimetals has been successfully sup-
ported on bentonite, a cheap and abundant clay, with the aid
of ionic liquid TMGL. The cations of TMGL are necessary
This journal is © The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 1000–1006 | 1005

View Online
for the excellent stability of the catalyst. Ru and Cu exhibits
excellent combination for catalyzing the hydrogenolysis of
aqueous glycerol to produce 1,2-PDO. The catalyst was most
efficient with a molar ratio of Ru to Cu of 3/1. 100% conversion
19 I. Furikado, T. Miyazawa, S. Koso, A. Shimao, K. Kunimori and K.
Tomishige, Green Chem., 2007, 9, 582–588.
0 C.-W. Chiu, A. Tekeei, J. M. Ronco, M.-L. Banks and G. J. Suppes,
2
Ind. Eng. Chem. Res., 2008, 47, 6878–6884.
21 T. Kurosaka, H. Maruyama, I. Naribayashi and Y. Sasaki, Catal.
Commun., 2008, 9, 1360–1363.
22 J. Chaminand, L. Djakovitch, P. Gallezot, P. Marion, C. Pinel and
C. Rosier, Green Chem., 2004, 6, 359–361.
of glycerol and 85% yield of 1,2-PDO could be achieved at
◦
2
30 C and 8 MPa. The catalyst modified with IL showed
excellent recyclability. We believe that more efficient catalysts
can be prepared by combination of functional ionic liquids, clays
and metals for different reactions.
2
2
2
2
3 L. Ma, D. H. He and Z. P. Li, Catal. Commun., 2008, 9, 2489–
2495.
4 J. Feng, H. Y. Fu, J. B. Wang, R. X. Li, H. Chen and X. J. Li, Catal.
Commun., 2008, 9, 1458–1464.
5 D. G. Lahr and B. H. Shanks, Ind. Eng. Chem. Res., 2003, 42, 5467–
5472.
6 D. G. Lahr and B. H. Shanks, J. Catal., 2005, 232, 386–394.
Acknowledgements
The authors wish to thank the National Natural Science
Foundation of China (20733010) for financial support.
27 C. Montassier, J. C. Menezo, L. C. Hoang, C. Renaud and J. Barbier,
J. Mol. Catal., 1991, 70, 99–110.
2
2
8 B. Casale and A. M. Gomez, US Pat., 5 276 181, 1994.
9 E. P. Maris, W. C. Ketchie, M. Murayama and R. J. Davis, J. Catal.,
2
007, 251, 281–294.
References
3
0 E. P. Maris and R. J. Davis, J. Catal., 2007, 249, 328–337.
1
2
3
4
T. Miyazawa, Y. Kusunoki, K. Kunimori and K. Tomishige, J. Catal.,
006, 240, 213–221.
G. W. Huber, J. N. Chheda, C. J. Barrett and J. A. Dumesic, Science,
005, 308, 1446–1450.
S. Fernando, S. Adhikari, C. Chandrapal and N. Murali, Energy
Fuels, 2006, 20, 1727–1737.
T. Werpy and G. Petersen, Top Value Added Chemicals from
Biomass, vol. 1, Results of Screening for Potential Candidates from
Sugars and Synthesis Gas, US DOE Report, 2004.
31 S. Wang and H. C. Liu, Catal. Lett., 2007, 117(1–2), 62–67.
32 M. Balaraju, V. Rekha, P. S. Sai Prasad, R. B. N. Prasad and N.
Lingaiah, Catal. Lett., 2008, 126, 119–124.
33 Z. W. Huang, F. Cui, H. X. Kang, J. Chen, X. Z. Zhang and C. G.
Xia, Chem. Mater., 2008, 20, 5090–5099.
34 A. P. Umpierre, G. Machado, G. H. Fecher, J. Morais and J. Dupont,
Adv. Synth. Catal., 2005, 347, 1404–1412.
35 C. P. Mehnert, E. J. Mozeleski and R. A. Cook, Chem. Commun.,
2002, 3010–3011.
2
2
5
6
7
8
9
C. S. Gong, J. X. Du, N. J. Cao and G. T. Tsao, Appl. Biochem.
36 J. Huang, T. Jiang, H. X. Gao, B. X. Han, Z. M. Liu, W. Z. Wu,
Y. H. Chang and G. Y. Zhao, Angew. Chem. Int. Ed., 2004, 43, 1397–
1399.
37 J. Huang, T. Jiang, B. X. Han, W. Z. Wu, Z. M. Liu, Z. L. Xie and
J. L. Zhang, Catal. Lett., 2005, 103, 59–62.
38 X. M. Ma, Y. X. Zhou, J. C. Zhang, A. L. Zhu, T. Jiang and B. X.
Han, Green Chem., 2008, 10(1), 59–66.
39 Y. L. Gu, C. Ogawa, J. Kobayashi, Y. Mori and S. Kobayashi, Angew.
Chem. Int. Ed., 2006, 45, 7217–7220.
40 M. R. Castillo, L. Fousse, J. M. Fraile, J. I. Garc ´ı a and J. A. Mayoral,
Chem.-Eur. J., 2006, 13, 287–291.
41 S. D. Miao, Z. M. Liu, B. X. Han, J. Huang, Z. Y. Sun, J. L. Zhang
and T. Jiang, Angew. Chem. Int. Ed., 2006, 45(2), 266–269.
42 T. Kawabata, T. Mizugaki, K. Ebitani and K. Kaneda, J. Am. Chem.
Soc., 2003, 125, 10486–10487.
Biotechnol., 2000, 84, 543–560.
P. L. Rogers, Y. J. Jeon and C. J. Svenson, Process Saf. Environ. Prot.,
2
005, 83, 499–503.
G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006, 106, 4044–
4
098.
M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and C. D. Pina,
Angew. Chem. Int. Ed., 2007, 46, 4434–4440.
A. Behr, J. Eilting, K. Irawadi, J. Leschinski and F. Lindner, Green
Chem., 2008, 10, 13–30.
1
1
0 C. H. Zhou, J. N. Beltramini, Y. X. Fan and G. Q. Lu, Chem. Soc.
Rev., 2008, 37, 527–549.
1 Y. G. Zheng, X. L. Chen and Y. C. Shen, Chem. Rev., 2008, 108,
5
253–5277.
1
1
1
1
1
2 D. Zimmerman and R. B. Isaacson, US Pat., 3 814 725, 1974 (Shell).
3 P. N. Caley and R. C. Everett, US Pat., 3 350 871, 1967 (DuPont).
4 E. P. Maris and R. J. Davis, J. Catal., 2007, 249, 328–337.
5 S. Ludwig and E. Manfred, US Pat., 5,616,817, 1997.
43 H. X. Gao, B. X. Han, J. C. Li, T. Jiang, Z. M. Liu, W. Z. Wu, Y. H.
Chang and J. M. Zhang, Synth. Commun., 2004, 34, 3083–3089.
44 S. Papp, J. Sz e´ l, A. Oszk o´ and I. D e´ k a´ ny, Chem. Mater., 2004, 16(9),
1674–1685.
6 C. Montassier, D. Giraud and J. Barbier, Stud. Surf. Sci. Catal., 1988,
´
1
65–170.
45 Z. Kir a´ ly, B. Veisz, A. Mastalir and Gy. K o¨ farag o´ , Langmuir, 2001,
1
1
7 M. A. Dasari, P.-P. Kiatsimkul, W. R. Sutterlin and G. J. Suppes,
Appl. Catal. A: Gen., 2005, 281, 225–231.
8 L. Huang, Y. L. Zhu, H. Y. Zheng, Y. W. Li and Z. Y. Zeng, J. Chem.
Technol. Biotechnol., 2008, 83, 1670–1675.
17(17), 5381–5387.
46 S. Aoki, K. Iwaida, N. Hanamoto, M. Shiro and E. Kimura, J. Am.
Chem. Soc., 2002, 124, 5256–5257.
47 P. J. Bailey and S. Pace, Coordin. Chem. Rev., 2001, 214, 91–141.
1
006 | Green Chem., 2009, 11, 1000–1006
This journal is © The Royal Society of Chemistry 2009