Hydrogenation of succinic acid to tetrahydrofuran over ruthenium-carbon composite catalyst: Effect of catalyst preparation condition

Article abstract of DOI:10.1166/jnn.2016.13250

Ruthenium-carbon composite (Ru-C-X) catalysts were prepared by a single-step surfactanttemplating method at different sucrose/P123 molar ratio (X = 3, 5, 7, 9, 11, and 15). Ru-C-X (X = 3, 5, 7, 9, 11, and 15) catalysts were characterized by BET, nitrogen adsorption-desorption isotherm, XRD, and HR-TEM analyses. Liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF) was carried out over Ru-C-X catalysts in a batch reactor. The effect of sucrose/P123 molar ratio on the physicochemical properties and catalytic activities of Ru-C-X catalysts (X = 3, 5, 7, 9, 11, and 15) was investigated. It was revealed that Ru-C-X composite catalysts showed different ruthenium particle size depending on sucrose/P123 molar ratio. Characterization results showed that an optimal sucrose/P123 molar ratio was required to achieve fine dispersion of ruthenium in the Ru-C-X catalysts. Yield for THF in the hydrogenation of succinic acid increased with decreasing average ruthenium particle size of Ru-C-X catalysts. Ruthenium particle size served as an important factor determining the catalytic performance of Ru-C-X in the hydrogenation of succinic acid to THF. Among the catalysts tested, Ru-C-9 with the smallest ruthenium particle size showed the highest yield for THF.

Full text of DOI:10.1166/jnn.2016.13250

Article
Journal of
Nanoscience and Nanotechnology
Vol. 16, 10841–10845, 2016
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Copyright © 2016 American Scientific Publishers
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Printed in the United States of America
Hydrogenation of Succinic Acid to Tetrahydrofuran Over
Ruthenium–Carbon Composite Catalyst: Effect of
Catalyst Preparation Condition
∗
Ung Gi Hong, Ki Hyuk Kang, Ji Hwan Song, Tae Hyeop Kim, and In Kyu Song
School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University,
Shinlim-dong, Kwanak-ku, Seoul 151-744, South Korea
Ruthenium–carbon composite (Ru–C-X) catalysts were prepared by a single-step surfactant-
templating method at different sucrose/P123 molar ratio (X = 3, 5, 7, 9, 11, and 15). Ru–C-X
(
X = 3, 5, 7, 9, 11, and 15) catalysts were characterized by BET, nitrogen adsorption–desorption
isotherm, XRD, and HR-TEM analyses. Liquid-phase hydrogenation of succinic acid to tetrahydro-
furan (THF) was carried out over Ru–C-X catalysts in a batch reactor. The effect of sucrose/P123
molar ratio on the physicochemical properties and catalytic activities of Ru–C-X catalysts (X = 3,
5
, 7, 9, 11, and 15) was investigated. It was revealed that Ru–C-X composite catalysts showed
different ruthenium particle size depending on sucrose/P123 molar ratio. Characterization results
showed that an optimal sucrose/P123 molar ratio was required to achieve fine dispersion of ruthe-
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nium in the Ru–C-X catalysts. Yield for THF in the hydrogenation of succinic acid increased with
IP: 5.101.222.79 On: Thu, 01 Dec 2016 13:13:26
decreasing average ruthenium particle size of Ru–C-X catalysts. Ruthenium particle size served
Copyright: American Scientific Publishers
as an important factor determining the catalytic performance of Ru–C-X in the hydrogenation of
succinic acid to THF. Among the catalysts tested, Ru–C-9 with the smallest ruthenium particle size
showed the highest yield for THF.
Keywords: Succinic Acid, Tetrahydrofuran, Ru–C Composite Catalyst, Mesoporous Carbon.
1
. INTRODUCTION
converted into THF.7–10 It is known that ruthenium is an
efficient catalyst in the hydrogenation of succinic acid
to THF, while carbon serves as an excellent supporting
Tetrahydrofuran (THF) is an important raw material
in various polymer industries. THF can be converted
into polytetramethylene ether glycol (PTMEG), thermo-
1
1–14
material for ruthenium.
Many researches on ruthe-
1
–3
plastic polyesters, and polyurethane elastomers.
THF
nium catalyst supported on carbon have been focused
on increasing ruthenium dispersion via carbon support
modification.
It has been reported that structure of carbon frame-
work prepared using a self-assembled block copolymer
is also widely used as a solvent in paint industries.
THF is traditionally produced via several industrial
routes such as oxidative hydrogenation of maleic anhy-
dride (MAN), acid-catalyzed dehydration of 1,4-butanediol
(
BDO), hydroformylation of ally alcohol, and oxidation
can be controlled by changing carbon precursor/block
4
–6
15ꢀ16
of butadiene (BD). Because all these feedstocks (MAN,
BDO, ally alcohol, and BD) are petrochemicals, the tradi-
tional THF production processes lead to several problems
such as unstable price and environmental issue. Therefore,
demands for finding an eco-friendly feedstock that can
solve these problems have continuously increased.
copolymer ratio.
In one-pot surfactant-templating
method (metal-carbon composite system), in particular,
structure of mesoporous carbon is very important
to increase metal dispersion, because metal particle
size of metal-carbon composite can be controlled by
changing carbon precursor/block copolymer ratio. If
metal-carbon composite is prepared to have control-
lable ruthenium dispersion, therefore, it can serve as an
excellent catalyst in the hydrogenation of succinic acid
with high catalytic activity. Furthermore, metal-carbon
Recently, succinic acid (SA) has attracted much atten-
tion as a cheap and bio-derived chemical that can be
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 10
1533-4880/2016/16/10841/005
doi:10.1166/jnn.2016.13250 10841

Hydrogenation of Succinic Acid to THF
Hong et al.
composite prepared by an one-pot surfactant-templating
method provides a simple preparation route.
2.3. Hydrogenation of Succinic Acid
Liquid-phase hydrogenation of succinic acid (SA) to THF
In this work, ruthenium–carbon composite (Ru–C-X)
catalysts were prepared by an one-pot surfactant-
templating method at different sucrose/block copolymer
molar ratio (X = 3ꢀ5ꢀ7ꢀ9ꢀ11ꢀ and 15) to control the
structure of ruthenium–carbon composite, i.e., to control
the ruthenium dispersion. The Ru–C-X catalysts were
was carried out over Ru–C-X (X = 3, 5, 7, 9, 11, and 15)
ꢀ
catalysts in a batch reactor at 240 C and 80 bar (H ꢄ. Suc-
2
cinic acid (0.5 g) and a reduced Ru–C-X catalyst (0.2 g)
were charged into an autoclave (150 ml). 1,4-Dioxane
(
50 ml) was used as a solvent for the reaction. The reac-
tor was purged with nitrogen to remove air, and then it
was pressurized up to 40 bar using hydrogen. After heat-
characterized by BET, N adsorption–desorption isotherm,
2
XRD, and HR-TEM analyses. Liquid-phase hydrogena-
tion of succinic acid to THF was performed over Ru–C-X
catalysts in a batch reactor. The effect of sucrose/block
copolymer molar ratio on the physicochemical proper-
ties and catalytic activities of ruthenium–carbon composite
ꢀ
ing the reactor to reaction temperature (240 C), hydrogen
pressure was raised up to 80 bar. The catalytic reaction
was carried out for 4 h. During the reaction, reaction mix-
ture was stirred at 500 rpm in order to avoid mass transfer
limitation. Reaction products were analyzed using a gas
chromatograph (Younglin, ACME-6100) equipped with a
FID (flame ionization detector).
(
Ru–C-X) catalysts was examined.
. EXPERIMENTAL DETAILS
3
. RESULTS AND DISCUSSION
Catalyst (Ru–C-X)
Known amounts of sucrose (3.2, 5.1, 6.6, 8.0, 9.2, and
1.3 g) (Aldrich) and surfactant (18.3, 17.1, 16.0, 15.0,
4.1, and 12.8 g) (P123, Aldrich) were dissolved in 5 M
HCl solution (300 ml) with ruthenium precursor (RuCl ,
3
.1. Physicochemical Properties of Ru–C-X Catalysts
Figure 1 shows the nitrogen adsorption–desorption
1
1
isotherms of Ru–C-X (X = 3, 5, 7, 9, 11, and 15) catalysts
ꢀ
reduced at 450 C. All the Ru–C-X catalysts exhibited
3
type-IV isotherm with type-H3 or type-H4 hysteresis loop,
indicating the existence of mesopores.
ꢀ
1
.27 g, Kojima Chemical) at 40 C for 4 h under stirring.
17ꢀ18
With increas-
After silica precursor (TEOS, 36 ml, Aldrich) and 0.4 M
of H SO (10 ml) were slowly added into the solution,
ing sucrose/P123 molar ratio of Ru–C-X (X = 3, 5, 7,
and 9) catalysts, type-H4 hysteresis loop was transformed
to more apparent type-H3 hysteresis loop. In the Ru–C-X
2
4
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the mixture was constantly stirred for 3 h. After the mix-
ꢀ
IP: 5.101.222.79 On: Thu, 01 Dec 2016 13:13:26
ture was dried at 100 C for 48 h, the resulting brown
Copyright: American S c( Xi en=ti f9 i c, 1P1 u, ba nl i sd h 1e 5r )s catalysts, however, type-H3 hysteresis
ꢀ
powder was carbonized at 800 C for 4 h at a heating
gradually disappeared with increasing sucrose/P123 molar
ꢀ
rate of 5 C/min under a nitrogen stream (100 ml/min).
ratio. Textural properties of Ru–C-X (X = 3, 5, 7, 9, 11,
The resultant was further treated with 5 wt% HF solu-
tion to remove silica template. The dried ruthenium–
carbon composite was then reduced with a mixed stream
ꢀ
and 15) catalysts reduced at 450 C are summarized in
Table I. Average pore size of Ru–C-X catalysts was in
the mesopore range (3.7–5.1 nm). BET surface area and
average pore volume of Ru–C-X showed a volcano-shaped
trend with respect to sucrose/P123 molar ratio. BET sur-
face area and average pore volume of Ru–C-X (X = 3,
of hydrogen (2.5 ml/min) and nitrogen (47.5 ml/min) at
ꢀ
4
50 C prior to characterization and catalytic reaction. The
ruthenium–carbon composite catalysts prepared at differ-
ent sucrose/P123 molar ratio (3, 5, 7, 9, 11, and 15) were
denoted as Ru–C-X, where X represented sucrose/P123
molar ratio.
Ru-C-15
Ru-C-11
2
.2. Characterization
Ru-C-9
Nitrogen adsorption–desorption isotherms of ruthenium–
carbon composite (Ru–C-X, X = 3, 5, 7, 9, 11, and 15)
catalysts were obtained with an ASAP-2010 instrument
Ru-C-7
Ru-C-5
(
Micromeritics). Surface areas and pore volumes of the
catalysts were calculated using the BET equation and the
BJH model, respectively. Crystalline state and ruthenium
particle size of Ru–C-X (X = 3, 5, 7, 9, 11, and 15) cat-
alysts were examined by XRD measurements. XRD pat-
terns of Ru–C-X (X = 3, 5, 7, 9, 11, and 15) catalysts
were obtained with a Rigaku D-Max2500-PC instrument
using Cu–Kꢁ radiation (ꢂ = 1ꢃ541 Å) operated at 50 kV
and 100 mA. Ruthenium particle size and ruthenium dis-
persion were examined by CO chemisorption (BELCAT-B,
BEL Japan) and HR-TEM (Jeol, JEM-3000F) analyses.
Ru-C-3
0
.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/Po)
Figure 1. Nitrogen adsorption–desorption isotherms of Ru–C-X cata-
ꢀ
lysts reduced at 450 C.
10842
J. Nanosci. Nanotechnol. 16, 10841–10845, 2016

Hong et al.
Hydrogenation of Succinic Acid to THF
Table I. Physicochemical properties of Ru–C-X catalysts.
catalyst was most finely dispersed on the carbon frame-
work. In order to determine the accurate dispersion of
ruthenium in the Ru–C-X catalysts, particle size of ruthe-
nium was calculated from XRD patterns using the Debye-
Ru particle size
By By CO
Surface
Pore
Average
area
volume pore size By
2
3
(
m /g-cat.) (cm /g-cat.) (nm) XRD HR-TEM chemisorption
2
1
Scherrer equation and CO chemisorption.
Ru–C-3
Ru–C-5
Ru–C-7
Ru–C-9
Ru–C-11
Ru–C-15
252
958
1016
1367
1082
672
0ꢃ23
0ꢃ89
0ꢃ93
1ꢃ38
1ꢃ19
0ꢃ85
3ꢃ7
3ꢃ7
3ꢃ8
4ꢃ0
4ꢃ4
5ꢃ1
20ꢃ9
8ꢃ9
4ꢃ2
3ꢃ2
3ꢃ8
24ꢃ3
10ꢃ4
5ꢃ9
4ꢃ1
5ꢃ3
32ꢃ4
11ꢃ7
5ꢃ4
3ꢃ9
4ꢃ2
Table I shows the average ruthenium particle sizes of
Ru–C-X catalysts determined by XRD and CO chemisorp-
tion measurements. Ruthenium particle sizes of Ru–C-X
catalysts determined by XRD and CO chemisorption
measurements showed the same trend with respect to
sucrose/P123 molar ratio. In the Ru–C-X (X = 3ꢀ5ꢀ7ꢀ
and 9) catalysts, ruthenium particle size became smaller
with increasing sucrose/P123 molar ratio. In the Ru–C-X
16ꢃ3
18ꢃ7
23ꢃ5
5
, 7, and 9) increased with increasing sucrose/P123 molar
ratio due to the increase of carbon framework formation
between sucrose and P123. In the Ru–C-X (X = 9ꢀ11ꢀ
and 15) catalysts, on the other hand, BET surface area and
average pore volume decreased due to the excess amount
of sucrose precursor. These results indicate that there is an
optimal sucrose/P123 ratio to form well-developed meso-
porous structure of carbon framework.
(
X = 9ꢀ11ꢀ and 15) catalysts, however, ruthenium particle
size increased with increasing sucrose/P123 molar ratio.
These might be explained by difference in mesoporos-
ity, as observed for the trends of BET surface area and
average pore volume of Ru–C-X catalysts with respect
to sucrose/P123 molar ratio. Because metal nanoparticles
tend to aggregate, it is important to form high surface area
and large pore volume for fine dispersion of ruthenium in
the ruthenium–carbon composite material. Thus, an opti-
mal sucrose/P123 molar ratio (X = 9) was required to yield
small ruthenium particles in the Ru–C-X catalysts.
3
.2. Crystalline State and Ruthenium Dispersion of
Ru–C-X Catalysts
Figure 2 shows the XRD patterns of Ru–C-X (X = 3, 5, 7,
ꢀ
9
, 11, and 15) catalysts reduced at 450 C. All the reduced
ꢀ
Figure 3 shows the HR-TEM images of Ru–C-X (X = 3,
Ru–C-X catalysts showed a weak shoulder at 2ꢅ = 25 ,
ꢀ
1
9
5, 7, 9, 11, and 15) catalysts reduced at 450 C. In the
which was attributed to graphitic carbon. All the reduced
Ru–C-X (X = 3ꢀ5ꢀ7ꢀ and 9) catalysts, ruthenium particle
Ru–C-X catalysts exhibited no XD Re lDi v ep reea dk sb yo fI nr ug teh ne tnai ut mo : Purdue University Libraries
size became smaller with increasing sucrose/P123 molar
IP: 5.101.222.79 On: Thu, 01 Dec 2016 13:13:26
oxide but showed XRD peaks of metallic ruthenium at
2
ꢀ
20
Copyright: American S rc ai tei on .t i fI inc tPh ue b Rl i us –h Ce r- sX catalysts (X = 9ꢀ11ꢀ and 15), how-
ꢅ = 44 . This result indicates that ruthenium species in
ever, ruthenium particle size became larger with increasing
sucrose/P123 molar ratio. In order to determine the ruthe-
nium particle size of Ru–C-X catalysts from HR-TEM
images, sizes of 200 metallic ruthenium particles in the
reduced catalysts were directly measured as also summa-
rized in Table I. It was observed that the trend of aver-
age ruthenium particle size determined by HR-TEM was
well consistent with the trend of ruthenium particle size
determined by XRD and CO chemisorption. Among the
Ru–C-X catalysts, Ru–C-9 catalyst showed the smallest
ruthenium particle size (less than 5 nm) while Ru–C-3
catalyst showed the largest ruthenium particle size (above
the Ru–C-X catalysts were completely reduced into metal-
lic ruthenium during the reduction process.
It was also observed that ruthenium peak inten-
sity of Ru–C-X catalysts decreased in the order of
Ru–C-3 > Ru–C-15 > Ru–C-5 > Ru–C-7 > Ru–C-11 >
Ru–C-9. This result indicates that ruthenium in the Ru–C-9
Graphitic Carbon
Ru
Ru-C-15
2
0 nm).
Ru-C-11
Ru-C-9
3
.3. Hydrogenation of Succinic Acid to THF Over
Ru–C-X Catalysts
Catalytic performance of Ru–C-X (X = 3, 5, 7, 9, 11,
and 15) catalysts in the liquid-phase hydrogenation of
succinic acid to THF is shown in Figure 4. THF and
ꢆ-butyrolactone (GBL) were mainly produced via consec-
utive hydrogenation of succinic acid. Ethanol was pro-
duced as a major by-product via side reaction of succinic
acid, and small amounts of acids (acetic acid, butyric acid,
and propionic acid) were also produced as by-products.
As shown in Figure 4, yield for THF showed a volcano-
shaped trend with respect to sucrose/P123 molar ratio.
Ru-C-7
Ru-C-5
Ru-C-3
2
0
30
40
50
60
70
2
Theta (degree)
ꢀ
Figure 2. XRD patterns of Ru–C-X catalysts reduced at 450 C.
J. Nanosci. Nanotechnol. 16, 10841–10845, 2016
10843

Hydrogenation of Succinic Acid to THF
(a) Ru-C-3
Hong et al.
(b) Ru-C-5
(c) Ru-C-7
(
d) Ru-C-9
(e) Ru-C-11
(f) Ru-C-15
ꢀ
Figure 3. HR-TEM images of Ru–C-X catalysts reduced at 450 C.
This means that an optimal sucrose/P123 molar ratio was
required for maximum production of THF. Among the
catalyst tested, Ru–C-9 catalyst showed the highest yield
for THF (45.3%), while Ru–C-3 catalyst showed the low-
5
0
Ru-C-9
Ru-C-11
Ru-C-7
40
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est yield for THF (12.1%). It is believed that the excellent
IP: 5.101.222.79 On: Thu, 01 Dec 2016 13:13:26
catalytic performance of Ru–C-9 catalyst was due to fine
3
0
Ru-C-5
Copyright: American Scientific Publishers
dispersion of ruthenium.
In order to investigate the effect of ruthenium disper-
sion of Ru–C-X (X = 3, 5, 7, 9, 11, and 15) catalysts
on the catalytic activity in the hydrogenation of succinic
acid, a correlation between average ruthenium particle size
of Ru–C-X catalysts and yield for THF was established.
Figure 5 shows the correlation between ruthenium particle
size of Ru–C-X catalysts (determined by HR-TEM) and
yield for THF in the hydrogenation of succinic acid. The
correlation clearly showed that yield for THF increased
2
1
0
0
Ru-C-3
Ru-C-15
2
4
21
18
15
12
9
6
3
Ruthenium particle size (nm)
Figure 5. A correlation between ruthenium particle size (determined by
HR-TEM) and catalytic activity of Ru–C-X catalysts in the hydrogena-
tion of succinic acid to THF.
6
5
4
3
2
1
0
0
0
0
0
0
0
GBL
THF
By-products
with decreasing ruthenium particle size (with increasing
ruthenium dispersion) of Ru–C-X catalysts. This result
strongly supports that ruthenium particle size of Ru–C-X
catalysts served as a key factor determining the catalytic
performance in the hydrogenation of succinic acid to THF.
4
. CONCLUSIONS
Ruthenium–carbon composite (Ru–C-X) catalysts were
prepared by a single-step surfactant-templating method at
different sucrose/P123 molar ratio (X = 3, 5, 7, 9, 11, and
1
5) to control the ruthenium dispersion of Ru–C-X cata-
lysts. They were then applied to the liquid-phase hydro-
genation of succinic acid to THF. Among the Ru–C-X
(X = 3, 5, 7, 9, 11, and 15) catalysts, Ru–C-9 catalyst
Ru-C-3 Ru-C-5 Ru-C-7 Ru-C-9 Ru-C-11 Ru-C-15
Figure 4. Catalytic performance of Ru–C-X catalysts.
10844
J. Nanosci. Nanotechnol. 16, 10841–10845, 2016

Hong et al.
Hydrogenation of Succinic Acid to THF
showed the smallest ruthenium particle size due to well-
developed mesoporous structure. In the hydrogenation of
succinic acid, yield for THF showed a volcano-shaped
trend with respect to sucrose/P123 molar ratio. Thus, an
optimal sucrose/P123 molar ratio in the preparation of
Ru–C-X composite catalysts was required to achieve max-
imum yield for THF. Yield for THF in the hydrogenation
of succinic acid increased with decreasing ruthenium par-
ticle size of Ru–C-X catalysts. Ruthenium particle size
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Copyright: American Scientific Publishers
Received: 3 July 2015. Accepted: 4 February 2016.
J. Nanosci. Nanotechnol. 16, 10841–10845, 2016
10845