Hydrogenation of succinic acid to tetrahydrofuran (THF) over rhenium catalyst supported on H2SO4-treated mesoporous carbon

Article abstract of DOI:10.1016/j.apcata.2011.12.022

Mesoporous carbon (MC) prepared by a surfactant-templating method was treated with different H₂SO₄ concentration (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 M) for use as a support (MC-X) for rhenium catalyst. Rhenium catalysts supported on H₂SO₄-treated mesoporous carbons (Re/MC-X) were then prepared by an incipient wetness impregnation method, and they were applied to the liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF). The effect of H₂SO₄ treatment on the physicochemical properties and catalytic activity of Re/MC-X catalysts (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) was investigated. It was observed that MC-X supports showed different pore characteristics depending on H₂SO ₄ concentration. As a result, Re/MC-X catalysts showed different rhenium particle size. In the liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF), conversion of succinic acid and yield for THF showed volcano-shaped curves with respect to H₂SO₄ concentration. Thus, an optimal H₂SO₄ concentration was required to achieve maximum catalytic performance of Re/MC-X. Yield for THF in the hydrogenation of succinic acid increased with decreasing rhenium particle size of Re/MC-X catalysts. Among the catalysts tested, Re/MC-0.4 with the smallest rhenium particle size showed the highest yield for THF.

Full text of DOI:10.1016/j.apcata.2011.12.022

Applied Catalysis A: General 415–416 (2012) 141–148
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Applied Catalysis A: General
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Hydrogenation of succinic acid to tetrahydrofuran (THF) over rhenium catalyst
supported on H2SO4-treated mesoporous carbon
Ung Gi Hong, Hai Woong Park, Joongwon Lee, Sunhwan Hwang, Jongheop Yi, 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
a r t i c l e i n f o
a b s t r a c t
Article history:
Mesoporous carbon (MC) prepared by a surfactant-templating method was treated with different H2SO4
concentration (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 M) for use as a support (MC-X) for rhenium catalyst. Rhenium
catalysts supported on H2SO4-treated mesoporous carbons (Re/MC-X) were then prepared by an incipient
wetness impregnation method, and they were applied to the liquid-phase hydrogenation of succinic acid
to tetrahydrofuran (THF). The effect of H2SO4 treatment on the physicochemical properties and catalytic
activity of Re/MC-X catalysts (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) was investigated. It was observed that MC-X
supports showed different pore characteristics depending on H2SO4 concentration. As a result, Re/MC-X
catalysts showed different rhenium particle size. In the liquid-phase hydrogenation of succinic acid to
tetrahydrofuran (THF), conversion of succinic acid and yield for THF showed volcano-shaped curves with
respect to H2SO4 concentration. Thus, an optimal H2SO4 concentration was required to achieve maximum
catalytic performance of Re/MC-X. Yield for THF in the hydrogenation of succinic acid increased with
decreasing rhenium particle size of Re/MC-X catalysts. Among the catalysts tested, Re/MC-0.4 with the
smallest rhenium particle size showed the highest yield for THF.
Received 30 September 2011
Received in revised form 7 December 2011
Accepted 13 December 2011
Available online 21 December 2011
Keywords:
Hydrogenation
Succinic acid
Mesoporous carbon
Rhenium
Tetrahydrofuran
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
catalysts such as platinum, palladium, ruthenium, and rhenium are
efficient in the hydrogenation of succinic acid to GBL [12,13]. For
Tetrahydrofuran (THF) is widely used as a solvent in various
industries. Polymerization of THF gives a raw material for manu-
facturing polytetramethylene ether glycol (PTMEG), thermoplastic
polyesters, and polyurethane elastomers [1–3]. THF is currently
produced via several routes including hydrogenation of maleic
anhydride (MAN) [4], dehydration of 1,4-butanediol (BDO) [5],
and oxidation of butadiene (BD) [6]. However, all these feedstocks
(MAN, BDO, and BD) are obtained from fossil fuels, leading to
unstable price and environmental problems. Therefore, demand
for finding a cheap and green chemical that can replace these
feedstocks has continuously increased [7–9]. Recently, conversion
of succinic acid to THF has attracted much attention, because of
the increase of succinic acid production in the biorefinery process
[10,11]. Succinic acid is a cheap and bio-based chemical that can be
converted into THF by hydrogenation reaction.
the production of THF, however, strong activity for hydrogenation
of carbonyl group is also required. Therefore, it is important to find
a suitable noble metal catalyst that has both cyclization activity
(SA → GBL) and oxidative-hydrogenation activity (GBL → THF) in
the hydrogenation of succinic acid to THF. It is known that rhenium
catalyst causes complete reduction of both carboxyl and carbonyl
groups, leading to further hydrogenation of GBL [14]. Therefore,
rhenium catalyst can be a potential candidate for selective produc-
tion of THF in the hydrogenation of succinic acid.
Noble metal catalysts have been generally used as supported
catalysts to increase metal dispersion, because of high price of noble
metal [15]. Therefore, it is also important to find efficient sup-
porting materials. Among various supporting materials, ordered
mesoporous carbon has found successful applications in many
reactions due to its well-developed porosity, non-toxicity, and
hydrophobic property [16–18]. In particular, regularly developed
mesoporosity of carbon support is a very important property to
increase metal dispersion in the supported noble metal catalyst
system. If carbon support is prepared to have a controllable pore
structure for increasing rhenium dispersion, therefore, it can serve
as an excellent support for rhenium catalyst to obtain hydrogena-
tion product of succinic acid with high catalytic activity.
Hydrogenation of succinic acid (SA) to THF follows two
consecutive reaction steps (Fig. 1). First, cyclization occurs
by hydrogenation of carboxyl group in succinic acid to form
␥-butyrolactone (GBL). Second, THF is formed via oxidative hydro-
genation of carbonyl group in GBL. It is known that noble metal
It has been reported that surface area and pore volume of
mesoporous carbon material prepared by a surfactant-templating
∗
Corresponding author. Tel.: +82 2 880 9227; fax: +82 2 889 7415.
E-mail address: inksong@snu.ac.kr (I.K. Song).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.12.022

142
U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
Fig. 1. Reaction pathways for the conversion of succinic acid.
method can be controlled by acid treatment [19,20]. Furthermore,
mesoporous carbon prepared by a surfactant-templating method
not only yields a highly ordered pore structure but also provides a
simple preparation route. Therefore, it is expected that mesoporous
carbon prepared by a surfactant-templating method can serve as an
excellent supporting material if it is properly treated.
In this work, mesoporous carbon (MC) was prepared by a
surfactant-templating method. MC was then treated with different
H2SO4 concentration with an aim of controlling pore character-
istics. Rhenium catalysts supported on H2SO4-treated MC were
prepared by an incipient wetness impregnation method. The sup-
ports and supported catalysts were characterized by FE-SEM,
HR-TEM, SAXS, N2 adsorption–desorption isotherm, and TPR analy-
ses. Liquid-phase hydrogenation of succinic acid to THF was carried
out over the supported rhenium catalysts in a batch reactor. The
effect of H2SO4 treatment on the physicochemical properties and
catalytic activity of supported rhenium catalysts was investigated.
different H2SO4 concentration (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 M)
was denoted as MC-X (MC-0, MC-0.2, MC-0.4, MC-0.6, MC-0.8, and
MC-1.0), where X represented H2SO4 concentration.
For comparison, porous carbon (PC) and carbon aerogel (CA)
supports were also prepared with H2SO4 treatment. For the prepa-
ration of porous carbon, a carbon precursor (sucrose, 8 g, Aldrich)
was dissolved in 4 M HCl solution (300 ml) at 40 ◦C. After a silica
precursor (TEOS, 36 ml, Aldrich) was slowly added into the solu-
tion, the resultant was dried at 100 ◦C. The resulting powder (20 g)
was then treated with 0.4 M H2SO4 solution (400 ml) for 12 h. After
drying the mixture at 160 ◦C for 8 h, the resulting solid was car-
bonized at 800 ◦C for 4 h at a heating rate of 5 ◦C/min in a nitrogen
stream (100 ml/min). The resultant was further treated with 5 wt%
HF solution to remove silica template. The porous carbon support
treated with 0.4 M H2SO4 solution was denoted as PC-0.4.
For the preparation of carbon aerogel, RF (resorcinol–
formaldehyde) sol–gel method was employed as reported in the
literatures [21,22]. 25.9 g of resorcinol (Aldrich) was dissolved in
60.0 ml of DI water. Aqueous resorcinol was mixed with Na2CO3
(0.05 g) to accelerate dehydrogenation of resorcinol. After stirring
the solution for a few minutes, 14.1 g of formaldehyde (Aldrich) was
slowly added into the solution to form a sol. The resulting sol was
heated to produce resorcinol–formaldehyde (RF) gel at 80 ◦C for
24 h. Acetone exchange was performed at 50 ◦C for two days. Resid-
ual solvent was replaced with fresh acetone every 3 h to remove
water thoroughly from the pore of RF wet gel. Ambient drying was
then done at room temperature for one day. The resulting solid
(20 g) was then treated with 0.4 M H2SO4 solution (400 ml) for 12 h.
After drying the mixture at 160 ◦C for 8 h, the solid was carbonized
at 800 ◦C for 4 h at a heating rate of 5 ◦C/min in a nitrogen stream
(100 ml/min). The carbon aerogel support treated with 0.4 M H2SO4
solution was denoted as CA-0.4.
2. Experimental
2.1. Preparation of supported rhenium catalysts
Fig. 2 shows the schematic procedures for the preparation of
mesoporous carbon (MC). A carbon precursor (sucrose, 8 g, Aldrich)
and P123 (tri-block copolymer surfactant, 16 g, Aldrich) were dis-
solved in 4 M HCl solution (300 ml) at 40 ◦C for 4 h under stirring.
After a silica precursor (TEOS, 36 ml, Aldrich) was slowly added into
the solution, the resultant was dried overnight at 100 ◦C. The result-
ing precipitate was washed and filtered with de-ionized water,
and it was then dried at 80 ◦C to obtain a sucrose/surfactant/silica
composite. To control pore characteristics, 20 g of composite was
treated with 400 ml of H2SO4 solution with different concentration
(0, 0.2, 0.4, 0.6, 0.8, and 1.0 M) for 12 h. After drying the mixture at
160 ◦C for 8 h, the resulting brown solid was carbonized at 800 ◦C for
4 h at a heating rate of 5 ◦C/min in a nitrogen stream (100 ml/min).
The resultant was further treated with 5 wt% HF solution to remove
silica template. The resulting mesoporous carbon treated with
Rhenium catalysts supported on H2SO4-treated carbons
(Re/MC-0, Re/MC-0.2, Re/MC-0.4, Re/MC-0.6, Re/MC-0.8, Re/MC-
1.0, Re/CA-0.4, and Re/PC-0.4) were prepared by an incipient
wetness impregnation method using an acetone solution of rhe-
nium chloride precursor (ReCl5, Aldrich). Rhenium loading was

U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
143
Fig. 2. Schematic procedures for the preparation of MC support.
fixed at 5 wt% in all the catalysts. After calcining the supported cat-
alysts at 500 ◦C in a nitrogen stream, they were dried overnight at
80 ◦C. The dried catalysts were then reduced with a mixed stream of
hydrogen (2.5 ml/min) and nitrogen (47.5 ml/min) at 450 ◦C prior
to the catalytic reaction.
temperature (240 ◦C), hydrogen pressure was raised up to 80 bar.
The catalytic reaction was carried out for 8 h. During the reaction,
reaction mixture 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). In order to investigate the stability of the cat-
alyst, the amount of rhenium leaching was measured by ICP-AES
(PerkinElmer, Optima-4300DV) measurements.
2.2. Characterization
Morphologies of carbon supports (MC-0, MC-0.2, MC-0.4, MC-
0.6, MC-0.8, and MC-1.0) were examined by FE-SEM analyses
(Jeol, JSM-6700F). Nitrogen adsorption–desorption isotherms of
supported catalysts (Re/MC-0, Re/MC-0.4, and Re/MC-0.8) were
obtained with an ASAP-2010 instrument (Micromeritics). Surface
areas and pore volumes of supported catalysts were calculated
using the BET equation and the BJH model, respectively. Crystalline
state of carbon supports was examined by SAXS (small-angle X-
ray scattering) measurements. SAXS patterns of MC-X supports
3. Results and discussion
3.1. Morphology and crystalline structure of MC-X supports
Fig. 3 shows the FE-SEM images of MC-X (X = 0, 0.2, 0.4, 0.6,
0.8, and 1.0) supports. Pore structure and surface morphology of
MC-X (X = 0, 0.2, and 0.4) supports showed fairly regular arrange-
ment with increasing H2SO4 concentration. On the other hand, pore
structure of MC-X (X = 0.6, 0.8, and 1.0) supports was collapsed with
increasing H2SO4 concentration. These results indicate that there
is an optimal H2SO4 concentration for obtaining well-developed
pore structure. It is reported that polymeric chains of surfactant
(P123) can be converted into carbon materials by dehydration
and calcination [19,20]. H2SO4 may act as a catalyst to dehy-
drate hydroxyl group of cross-linked polymer chain of P123. These
cross-linked polymer chains are converted into carbon materials
during the calcination step. This means that surfactant performs
the role of template framework as well as the role of carbon source
together with sucrose. However, H2SO4 treatment at high con-
centration may cause destruction of pore channel. Therefore, an
optimal H2SO4 concentration was required to obtain ordered meso-
porosity in the surfactant-templating method. Among the MC-X
supports, MC-0.4 support showed the most regular pore structure
and surface morphology.
˚
were obtained with a Bruker GADDS instrument using ꢀ = 1.54 A
radiation. Rhenium dispersion was examined by HR-TEM (Jeol,
JEM-3000F) analyses. Hydrogen uptake and metal–support inter-
action of supported catalysts (Re/CA-0.4, Re/PC-0.4, and Re/MC-X)
were examined by TPR (temperature programmed reduction)
experiments using a conventional flow system equipped with a TCD
(thermal conductivity detector) at temperatures ranging from 150
to 450 ◦C with a ramping rate of 5 ◦C/min. For TPR measurements,
a mixed stream of H2 (2 ml/min) and N2 (20 ml/min) was used for
0.05 g of catalyst sample.
2.3. Hydrogenation of succinic acid
Liquid-phase hydrogenation of succinic acid (SA) to THF was
carried out over supported rhenium catalysts in a batch reactor at
240 ◦C and 80 bar (H2). Succinic acid (0.5 g) and a reduced cata-
lyst (0.2 g) were charged into an autoclave (150 ml). 1,4-Dioxane
(50 ml) was used as a solvent for the reaction. The reactor was
purged with nitrogen to remove air, and then it was pressurized
up to 40 bar using hydrogen. After heating the reactor to reaction
In order to investigate accurate crystalline structure of MC-X
(X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) supports, SAXS analyses were per-
formed. Fig. 4 shows the SAXS patterns of MC-X supports. The
(1 0 0), (1 1 0), and (2 0 0) reflections appeared in MC-0.2, MC-0.4,

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U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
Fig. 3. FE-SEM images of MC-X supports.
and MC-0.6 samples. In particular, MC-0.4 showed the most obvi-
ous scattering peaks. These three characteristic peaks correspond
to diffraction of 2-D hexagonal space group (p6mm), demonstrat-
ing long-range ordering of carbon material [23,24]. This implies
that MC-0.4 support has the most regular pore structure among
the MC-X supports.
HR-TEM images of MC-0.4 support are shown in Fig. 5. It
was clearly observed that MC-0.4 was composed of 2-D hexag-
onally ordered nanorod array (diameter of the carbon rod is ca.
6 nm). These HR-TEM images strongly indicate that MC-0.4 support
retains regular structure and mesoporosity.
3.2. Physical properties of Re/MC-X catalysts
Physical properties of Re/MC-X catalysts (X = 0, 0.2, 0.4, 0.6,
0.8, and 1.0) are summarized in Table 1. Re/MC-0.4 support
showed the highest surface area (1124 m2/g) and largest pore vol-
ume (1.62 cm3/g). Surface area and pore volume increased with
increasing H2SO4 concentration in the Re/MC-X (X = 0, 0.2, and
0.4) catalysts. On the other hand, surface area and pore volume
decreased with increasing H2SO4 concentration in the Re/MC-
X (X = 0.4, 0.6, 0.8, and 1.0) catalysts. Moreover, micropore was
developed at high H2SO4 concentration. This means that H2SO4
treatment at high concentration may cause destruction of pore
channel, leading to the increase of microporosity and the decrease
of mesoporosity. As listed in Table 1, surface area and pore vol-
ume of the catalysts showed volcano-shaped trends with respect
to H2SO4 concentration.
MC-0
MC-0.2
(100)
(110)
(200)
MC-0.4
MC-0.6
Table 1
MC-0.8
MC-1.0
2.5
Physical properties of Re/MC-X catalysts.
Surface area
(m2/g-cat.)
Micropore area
(m2/g-cat.)
Pore volume
(cm3/g-cat.)
Re/MC-0
868
911
1124
906
596
448
–
–
–
107
284
274
1.25
1.30
1.62
1.31
0.68
0.42
Re/MC-0.2
Re/MC-0.4
Re/MC-0.6
Re/MC-0.8
Re/MC-1.0
1.0
1.5
2.0
3.0
2 Theta (degree)
Fig. 4. SAXS patterns of MC-X supports.

U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
145
Fig. 5. HR-TEM images of MC-0.4 support.
Fig. 6 shows the nitrogen adsorption–desorption isotherms of
Re/MC-X (X = 0, 0.4, and 0.8) catalysts. All the Re/MC-X catalysts
showed type-IV isotherms. Both Re/MC-0 and Re/MC-0.4 cata-
lysts showed type-H3 hysteresis loop, indicating the existence of
mesoporosity [25]. In particular, Re/MC-0.4 showed more apparent
type-H3 hysteresis loop than Re/MC-0 catalyst. This implies that
mesoporosity of Re/MC-0.4 was developed by H2SO4 treatment.
On the other hand, Re/MC-0.8 catalyst showed type-H4 hysteresis
loop, indicating the increase of microporosity. These physical prop-
erties of Re/MC-X catalysts were well consistent with FE-SEM and
SAXS results of MC-X supports (Figs. 3 and 4). The above results
indicate that pore structure of MC-X supports could be controlled
by changing H2SO4 treatment concentration.
catalysts (X = 0, 0.2, and 0.4), rhenium particle size became smaller
with increasing H2SO4 concentration. In the Re/MC-X catalysts
(X = 0.6, 0.8, and 1.0), however, rhenium particle size became larger
with increasing H2SO4 concentration. These were well consistent
with the trends of surface area and pore volume of MC-X supports
(Table 1) with regard to H2SO4 concentration. It is known that large
pore volume and ordered mesoporosity are mainly responsible for
enhancing dispersion of metal particle in the supported metal cata-
lyst. Therefore, Re/MC-0.4 catalyst with the largest pore volume and
most regular mesoporous structure showed the smallest rhenium
particle size (less than 5 nm) among the Re/MC-X catalysts.
In order to ensure the trend of rhenium dispersion (rhenium
particle size) of Re/MC-X catalysts, TPR measurements were con-
ducted. TPR results of Re/MC-X catalysts are shown in Fig. 8. With
increasing H2SO4 concentration, reduction peak temperature of
Re/MC-X catalysts (X = 0, 0.2, and 0.4) decreased, while that of
Re/MC-X (X = 0.6, 0.8, and 1.0) catalysts increased. In other words,
metal–support interaction of Re/MC-X catalysts (X = 0, 0.2, and 0.4)
decreased while that of Re/MC-X (X = 0.6, 0.8, and 1.0) increased
with increasing H2SO4 concentration. Interestingly, the trend of
TPR peak temperature was well consistent with the trend of surface
area and pore volume of MC-X supports (Table 1).
3.3. Rhenium particle size and metal–support interaction of
Re/MC-X catalysts
Fig. 7 shows the HR-TEM images of Re/MC-X catalysts (X = 0,
0.2, 0.4, 0.6, 0.8, and 1.0) reduced at 450 ◦C. In the Re/MC-X
Table 2 shows the hydrogen uptake and rhenium particle size
of Re/MC-X (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) catalysts. Rhenium
particle size and hydrogen uptake were calculated on the basis
of TPR peak area using the equations in literatures [26,27]. Rhe-
nium particle size of Re/MC catalysts showed the same trend as
TPR peak temperature with respect to H2SO4 concentration. This
means that rhenium particle is finely dispersed on the MC sup-
port when the metal–support interaction is weak. It is believed that
small metal particle has a weak interaction with the support due
to small interfacial area between two solids by geometric effect
[28,29]. In other words, when the interaction between metal and
support is stronger, metal particle can spread out over the support,
Table 2
Hydrogen uptake and rhenium particle size of Re/MC-X catalysts.
Hydrogen uptake
(mmol/g-cat.)
Rhenium particle
size (nm)
Re/MC-0
1.57
3.27
3.66
2.44
1.07
0.51
9.1
4.4
3.9
5.8
13.3
27.8
Re/MC-0.2
Re/MC-0.4
Re/MC-0.6
Re/MC-0.8
Re/MC-1.0
Fig. 6. Nitrogen adsorption–desorption isotherms of Re/MC-X catalysts reduced at
450 ◦C.

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U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
Fig. 7. HR-TEM images of Re/MC-X catalysts reduced at 450 ◦C.
so that the metal particle size becomes larger. For this reason,
Re/MC-X catalyst with smaller rhenium particle size and higher
hydrogen uptake capacity showed lower reduction temperature
in TPR profile. Among the Re/MC-X catalysts, Re/MC-0.4 catalyst
showed the smallest rhenium particles (3.9 nm) and the highest
hydrogen uptake capacity (3.66 mmol/g-cat.), while Re/MC-1.0 cat-
alyst showed the largest rhenium particle size (27.8 nm) and the
smallest hydrogen uptake capacity (0.51 mmol/g-cat.). Once again,
it is noticeable that rhenium particle size (Table 2), TPR peak tem-
perature (Fig. 8), and surface area and pore volume of supports
(Table 1) showed the same trends with respect to H2SO4 treatment
concentration.
of succinic acid, and small amounts of acetic acid and butyric acid
were also produced as by-products. It is known that rhenium is an
effective catalyst for hydrogenolysis and oxidative-hydrogenation
[14,30,31]. Therefore, the side reaction (formation of ethanol)
competitively occurred together with hydrogenation of succinic
acid (formation of THF) over the supported rhenium catalyst.
3.4. Hydrogenation of succinic acid (SA) over Re/MC-X catalysts
Catalytic performance of Re/MC-X catalysts (X = 0, 0.2, 0.4, 0.6,
0.8, and 1.0) in the liquid-phase hydrogenation of succinic acid
(SA) is shown in Table 3. ␥-Butyrolactone (GBL), tetrahydrofuran
(THF), and 1,4-butanediol (BDO) were produced as main products
via hydrogenation of succinic acid. Ethanol was mainly produced
as a by-product via hydrogenolysis and oxidative-hydrogenation
Table 3
Catalytic performance of Re/MC-X catalysts in the liquid-phase hydrogenation of
succinic acid (reaction temperature = 240 ◦C; reaction pressure = 80 bar; reaction
time = 8 h).
Conversion
of SA (%)
Yield (%)
GBL
THF
BDO
By-products
Re/MC-0
80.4
99.4
100
85
61.8
51.3
62.2
48.6
26.8
61.1
44.9
38.1
7.3
26.4
38.3
8.9
5.1
3.6
3.1
3.1
4.5
3.4
3.1
2.4
7.8
21.3
30.4
11.6
8.7
Re/MC-0.2
Re/MC-0.4
Re/MC-0.6
Re/MC-0.8
Re/MC-1.0
7.2
Fig. 8. TPR profiles of Re/MC-X catalysts.

U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
147
Table 4
Result for liquid-phase hydrogenation of succinic acid over Re/MC-0.4 catalyst with
respect to recycle run (reaction temperature = 240 ◦C; reaction pressure = 80 bar;
reaction time = 8 h).
100
80
60
40
20
0
100
80
60
40
20
0
Recycle
run
Conversion
of SA (%)
Yield for
THF (%)
Rhenium leachinga
(ppm)
1
2
3
100
100
100
38.1
37.4
37.2
0.84
0.77
0.61
a
Determined by ICP-AES analyses.
3.5. Stability and reusability of Re/MC-X catalyst
To investigate the stability and reusability of the catalyst, recycle
tests for hydrogenation of succinic acid over Re/MC-0.4 cata-
lyst were performed three times. Table 4 shows the result for
liquid-phase hydrogenation of succinic acid to THF over Re/MC-
0.4 catalyst with respect to recycle run. It was found that fresh and
spent catalysts showed similar catalytic activity. Furthermore, no
significant rhenium leaching (less than 1.0 ppm) was detected by
ICP-AES analysis after each reaction test. Thus, Re/MC-0.4 catalyst
served as a stable and reusable catalyst in the hydrogenation of
succinic acid to THF.
Re/MC-0.8
Re/MC-0.2 Re/MC-0.4 Re/MC-0.6
Re/MC-1.0
Re/MC-0
Catalyst
Fig. 9. Catalytic activity of Re/MC-X catalysts in the liquid-phase hydrogenation
of succinic acid to THF (reaction temperature = 240 ◦C; reaction pressure = 80 bar;
reaction time = 8 h).
Fig. 9 shows the catalytic performance of Re/MC-X catalysts in
the liquid-phase hydrogenation of succinic acid. It is noteworthy
that both conversion of succinic acid and yield for THF showed
volcano-shaped curves with respect to H2SO4 concentration. This
means that an optimal H2SO4 concentration was required for max-
imum catalytic performance. Among the catalyst tested, Re/MC-0.4
catalyst showed the highest conversion of succinic acid (100%) and
the highest yield for THF (38.3%), while Re/MC-1.0 catalyst showed
the lowest conversion of succinic acid (51.3%) and the lowest yield
for THF (3.6%). It is believed that the excellent catalytic performance
of Re/MC-0.4 catalyst was due to the smallest rhenium particle size
(the highest rhenium dispersion).
In order to investigate the effect of rhenium particle size of
Re/MC-X catalysts on the catalytic activity in the hydrogenation
of succinic acid, a correlation between rhenium particle size of
Re/MC-X catalysts and yield for THF was established. Fig. 10 shows
the correlation between rhenium particle size of Re/MC-X cata-
lysts and yield for THF in the hydrogenation of succinic acid. It
was observed that yield for THF increased with decreasing rhenium
particle size (with increasing rhenium dispersion) of Re/MC-X cat-
alysts. This result strongly supports that rhenium particle size of
Re/MC-X catalysts served as an important factor determining the
catalytic performance in the hydrogenation of succinic acid to THF.
3.6. Comparison of catalytic performance of supported rhenium
catalysts (Re/CA-0.4, Re/PC-0.4, and Re/MC-0.4)
Catalytic performance of Re/CA-0.4, Re/PC-0.4, and Re/MC-0.4
in the liquid-phase hydrogenation of succinic acid to THF is shown
in Fig. 11. In the hydrogenation of succinic acid over Re/CA-0.4 and
Re/PC-0.4 catalysts, ␥-butyrolactone (GBL), tetrahydrofuran (THF),
and 1,4-butanediol (BDO) were also produced as main products via
hydrogenation of succinic acid. In the comparison test, Re/MC-0.4
catalyst showed the highest conversion of succinic acid (100%) and
the highest yield for THF (38.3%). Re/CA-0.4 and Re/PC-0.4 cata-
lysts showed lower conversion of succinic acid (60.9% and 72.3%,
respectively) and lower yield for THF (4.1% and 5.2%, respectively)
than Re/MC-0.4 catalyst. It is believed that the excellent catalytic
performance of Re/MC-0.4 catalyst was due to the smallest rhe-
nium particle size. Rhenium particle size of Re/MC-0.4 catalyst was
3.9 nm (Table 2), while that of Re/CA-0.4 and Re/PC-0.4 catalysts
was 15.5 nm and 9.7 nm, respectively. This result also supports that
rhenium particle size of the supported catalysts served as a key
factor determining the catalytic performance in the hydrogenation
of succinic acid to THF.
100
Conversion of succinic acid
Yield for THF
80
60
40
20
0
Re/CA-0.4
Re/PC-0.4
Re/MC-0.4
Fig. 11. Comparison of catalytic performance of Re/CA-0.4, Re/PC-0.4, and Re/MC-
0.4 in the hydrogenation of succinic acid to THF (reaction temperature = 240 ◦C;
reaction pressure = 80 bar; reaction time = 8 h).
Fig. 10. A correlation between rhenium particle size of Re/MC-X catalysts and cat-
alytic activity in the hydrogenation of succinic acid to THF.

148
U.G. Hong et al. / Applied Catalysis A: General 415–416 (2012) 141–148
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This subject is supported by Korea Ministry of Environment as
“Converging Technology Project (202-091-001)”.
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