Catalytic transfer hydrogenation/hydrogenolysis of guaiacol to cyclohexane over bimetallic RuRe/C catalysts

Article abstract of DOI:10.1016/j.catcom.2016.08.022

The hydrodeoxygenation of lignin monomer guaiacol via catalytic transfer hydrogenation was studied with 2-propanol as a hydrogen donor and Ru-based catalysts. Guaiacol was mainly converted into a partially deoxygenated product, cyclohexanol (>?70% selectivity), over Ru/C catalysts with the hydrogen produced in-situ from 2-propanol. An addition of Re to Ru/C catalysts significantly enhanced the rate of C—O hydrogenolysis, resulting in the complete deoxygenation to cyclohexane (~?60% selectivity). The remarkable deoxygenation ability of the bimetallic RuRe/C catalyst is attributed to its bifunctional characteristic, by which Ru catalyzes the hydrogenation-hydrogenolysis of guaiacol and Re provides acid sites to promote cyclohexane production via hydrogenolysis.

Full text of DOI:10.1016/j.catcom.2016.08.022

Catalysis Communications 86 (2016) 113–118
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Catalytic transfer hydrogenation/hydrogenolysis of guaiacol to
cyclohexane over bimetallic RuRe/C catalysts
Mookyung Kim a,b, Jeong-Myeong Ha a,c,d, Kwan-Young Lee b,c, Jungho Jae a,d,
⁎
a
Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
Department of Chemical and Biological Engineering, Korea University, Seoul 02841, Republic of Korea
Green School, Korea University, Seoul 02841, Republic of Korea
b
c
d
Department of Clean Energy and Chemical Engineering, Korea University of Science and Technology, Daejeon 34113, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 May 2016
Received in revised form 22 July 2016
Accepted 16 August 2016
Available online 17 August 2016
The hydrodeoxygenation of lignin monomer guaiacol via catalytic transfer hydrogenation was studied with 2-
propanol as a hydrogen donor and Ru-based catalysts. Guaiacol was mainly converted into a partially deoxygen-
ated product, cyclohexanol (N70% selectivity), over Ru/C catalysts with the hydrogen produced in-situ from 2-
propanol. An addition of Re to Ru/C catalysts significantly enhanced the rate of C—O hydrogenolysis, resulting
in the complete deoxygenation to cyclohexane (~60% selectivity). The remarkable deoxygenation ability of
the bimetallic RuRe/C catalyst is attributed to its bifunctional characteristic, by which Ru catalyzes the hydroge-
nation-hydrogenolysis of guaiacol and Re provides acid sites to promote cyclohexane production via
hydrogenolysis.
Keywords:
Biomass
Transfer hydrogenation
Bimetallic
RuRe
© 2016 Elsevier B.V. All rights reserved.
Guaiacol
1. Introduction
can be provided by either the support or added promoters. For in-
stances, Lee et al. reported that Rh/silica-alumina is highly active for
Lignocellulosic biomass has been widely studied as a renewable
feedstock for the production of fuels and chemicals. Fast pyrolysis is a
promising technology to convert solid biomass into a liquid fuel called
a bio-oil [1]. However, the fuel quality of the bio-oils is very low because
they are highly oxygenated and are not compatible with the existing pe-
troleum-derived oils [2]. Catalytic hydrodeoxygenation (HDO) is an ef-
fective method to convert bio-oils into high-grade fuels by selectively
removing oxygen from bio-oils [3]. Therefore, many researchers have
focused on the development of highly active and stable catalysts for
the HDO of bio-oils.
Guaiacol is a representative bio-oil model compound because it con-
tains two types of C—O bonds, hydroxyl (Csp2OH) and methoxy
(Csp2OCH3), which are prevalent in the phenolic compounds of bio-
oils [4]. The HDO of guaiacol has been studied using a range of catalysts,
including metal sulfides (NiMoS and CoMoS), noble metals (Pt, Rh), and
non-noble transition metals (Ni, Fe) [3]. In general, noble metals such as
Pt show higher HDO activity, but the undesired hydrogenation of the ar-
omatic ring is favored, leading to high H2 consumption. Combining
metal sites with acid sites has been suggested as an effective means of
enhancing the deoxygenation activity of catalysts [5–9]. The acid sites
the hydrodeoxygenation of guaiacol due to the synergistic effect of
metal-catalyzed hydrogenation and acid-catalyzed dehydration [6].
Wang et al. reported that the addition of Fe to Ni/SiO2 substantially en-
hanced the deoxygenation activity of m-cresol [8].
In addition to catalyst development, the HDO conditions are an im-
portant issue because the HDO of bio-oils typically involves harsh reac-
tion conditions, such as high temperatures (573–723 K) and high H2
pressure, both of which increase the process costs. Catalytic transfer hy-
drogenation (CTH) is an efficient method for the reduction of carbonyl
groups without using molecular H2 at moderate temperatures [10]. Sev-
eral groups have reported the effectiveness of the CTH process for re-
ducing the oxygen content in a range of biomass-derived molecules,
such as glycerol [11,12], levulinic acid [13,14], furfural [15–17] using
secondary alcohols (e.g., 2-propanol) or formic acid as hydrogen donors.
However, reports of the CTH of phenolic compounds such as guaiacol
are scarce. There have been only limited studies using Raney Ni and
Pd/C catalysts [18,19].
In this study, we investigate the catalytic transfer hydrogenation/
hydrogenolysis of guaiacol to cyclohexane using 2-propanol as a hydro-
gen donor over Ru-based catalysts. Ru shows activity superior to
those of Ni and Pd for the dehydrogenation of 2-propanol and the
hydrodeoxygenation of guaiacol. The Re promotion of the Ru/C catalysts
further enhances the rate of C—O hydrogenolysis, resulting in high
selectivity toward cyclohexane (~60%).
⁎
Corresponding author at: Clean Energy Research Center, Korea Institute of Science and
Technology, Seoul 02792, Republic of Korea.
E-mail address: jjae@kist.re.kr (J. Jae).
http://dx.doi.org/10.1016/j.catcom.2016.08.022
1566-7367/© 2016 Elsevier B.V. All rights reserved.

114
Short communication
2. Experimental
2.1. Catalyst preparation
5 wt% Ru/C and 10 wt% Ni/C catalysts were prepared by incipient
wetness impregnation method. Activated charcoal was impregnated
with aqueous solutions of RuCl3·xH2O and Ni(NO3)2·6H2O, respective-
ly. After drying at 383 K for 10 h, Ru/C and Ni/C were reduced at 573 K
and at 673 K, respectively, in a flowing mixture of H2 (5%) and N2
(95%). 5 wt% Pd/C and 5 wt% Ru/Al2O3 catalysts were directly purchased
from Sigma Aldrich and reduced at 573 K before reaction. Bimetallic
RuRe/C catalysts were prepared by successive impregnation. 4 wt%
Ru/C catalysts were prepared and dried at 378 K. The dried Ru/C cata-
lysts were then impregnated with aqueous solution of NH4ReO4. The
loading amount of Re was varied based on an atomic ratio (atomic
ratio of Re/Ru = 0.25, 0.5, 0.75). For comparison, Re/C catalyst was
also prepared by incipient wetness impregnation with aqueous solution
of NH4ReO4. After impregnation, the catalysts were dried in air (383 K)
and were reduced at 523 K in flowing H2. 5 wt% Ru/H-BEA catalyst was
prepared by impregnation of H-Beta zeolite (H-BEA, SiO2/Al2O3 = 38,
Zeolyst) with an aqueous solution of RuCl3·xH2O.
Fig. 1. H2-TPR profiles of Ru/C, Re/C, and RuRe/C catalysts with Re/Ru atomic ratios of 0.25,
0.5, and 0.75. Before TPR measurements, the catalysts were treated under 5% O2/He flow at
403 K for 1 h.
for the CTH of guaiacol. Table 1 illustrates the conversion and product
selectivity over different catalysts. The conversion of guaiacol decreased
in the order Ru/C N Pd/C N Ni/C. Importantly, the conversion of 2-
propanol also decreased in the order Ru/C N Pd/C N Ni/C, implying that
the rate of 2-propoanol dehydrogenation is closely related to the rate
of CTH of guaiacol. Ni/C exhibited significantly lower conversion of
guaiacol (17%) than those of Ru/C (99%) and Pd/C (90%), respectively.
This could be due to the lower Ni dispersion (0.98%) and slower dehy-
drogenation rate of 2-propanol over Ni/C. The turnover frequency
(TOF) value of Ni/C was comparable to that of Ru/C. Regarding product
selectivity, the major products over Ru/C are cyclohexanol (70.2%) and
2-methoxycyclohexanol (11.4%), indicating that hydrogenation of the
aromatic ring and demethoxylation readily occur through CTH with
Ru/C. Ni/C showed a similar product distribution to Ru/C, producing
cyclohexanol (47.7%), 2-methoxycyclohexanol (23.6%), and phenol
(15%) as the main products. The formation of phenol over Ni/C indicates
that the hydrogenation of the aromatic ring over Ni/C is slower than that
over noble metal catalysts, similar to results reported by other groups
[3]. Meanwhile, Pd/C showed a significantly different product distribu-
tion from Ru/C. Etherified products of 2-propanol and the hydrogenated
guaiacol intermediates (e.g., 1-isopropoxy-2-methoxycyclohexane,
isopropoxybenzene) are the major products (55.8%) along with a lesser
amount of 2-methoxycyclohexanol (18%). This result implies that Pd/C
catalyzes the undesired etherification reaction in parallel with the
hydrogenation of guaiacol. Overall, the Ru/C catalyst showed the best
performance for the CTH of guaiacol, giving the highest yield of
cyclohexanol.
2.2. Characterization
CO-chemisorption was performed using a pulsed injection of 10%
CO/He (50 sccm) with a BETCAT-B (BEL JAPAN) equipped with a ther-
mal conductivity detector. The reducibility of Ru and Re metals was
characterized by temperature programmed reduction (TPR) using a
BETCAT-B. TPR was carried out under 5% H2/Ar flow (30 sccm) from
303 K to 1173 K with a heating rate of 10 K/min. The TEM images
were obtained with a FEI Talos F200X transmission electron microscopy
(TEM). Energy dispersive X-ray spectroscopy (EDX) mapping analyses
were also conducted using the same microscope to examine the de-
tailed distribution of Ru and Re on the carbon support.
2.3. Catalytic experiments
Reactions were performed in a stainless steel 150 mL Parr reactor.
For a typical reaction, 0.25 g of guaiacol (99%, Sigma Aldrich), 25 mL of
2-propanol (99.9%, Sigma Aldrich), and 0.1 g of the catalysts were
charged in the reactor. The reactor was sealed and pressurized with
N2 to 2 MPa. The reactor was then heated up to 473–513 K using an elec-
trical furnace and stirred at 300 50 rpm with a gas entrainment im-
peller. After the designated reaction time, the liquid products were
collected, filtered, and analyzed by means of a gas chromatography
(Agilent 7890B) equipped with a flame ionization detector (FID).
3. Results and discussion
In order to produce the fully deoxygenated cyclohexane from
guaiacol, a combination of acidic supports and Ru metal was investigat-
ed. Alumina (Al2O3) and H-Beta zeolite (H-BEA) were selected to probe
the reactivity of Lewis and Brønsted acid sites in the reaction, respec-
tively. Ru/Al2O3 showed similar guaiacol conversion and product selec-
tivity to Ru/C, indicating that Lewis acids do not promote the
3.1. Catalyst screening for the CTH of guaiacol
Initial experiments focused on the investigation of the activity of
several monometallic catalysts (Ni, Pd, and Ru) supported on carbon
Table 1
Conversion and product selectivity for the CTH of guaiacol in 2-propanol as a solvent at 473 K for 5 h with various catalysts.
Entry Catalyst
Conv. (%) Sel. (%)
Cyclohexane Cyclohexanol 2-Methoxy cyclohexanol Phenol Others Ethers
TOF (h−1
)
IPA Conv. (%) Sel. (%) from IPA
Acetone Isopropyl ether
81.9 16.8
1
2
3
4
5
Ni/C
Pd/C
Ru/C
Ru/Al2O3
17.5
89.3
99.3
99.3
1.6
9.9
0.8
2.2
–
47.7
1.8
70.2
60.4
–
23.6
18.3
11.4
12.9
–
14.7
–
–
–
–
3471
2359
3767
–
3.5
4.8
2.7
4.1
–
55.8
4.0
9.0
77.5
5.1
48.5 47.4
8.0
13.0
42.3
83.0
97.3
–
16.6
2.0
94.5
–
Ru/H-BEA 9.9
–
–
Others are 1,2-cyclohexanediol and cyclohexanone.
Ethers include 1-isopropoxy-2-methoxybenzene, 1-isopropoxy-2-methoxycyclohexane, isopropoxy benzene, and isopropoxycyclohexane.
TOF was calculated based on the guaiacol conversion (at conversion b 20%).

Short communication
115
Table 2
as Ru and Ir, the noble metals can promote the reduction of the other
metal due to hydrogen transfer from their reduced species [25,26].
Therefore, these results suggest that Ru and Re are in close contact on
the carbon support, by which hydrogen adsorbed on reduced rutheni-
um species can easily be transferred to unreduced neighboring rhenium
species during the reduction process. In addition, the amounts of H2 up-
take of the catalysts were calculated from the TPR profiles (see Table
S1). It was found that the amount of H2 uptake of the RuRe/C (0.5)
was larger compared to the sum of individual amount of H2 uptake of
Ru/C and Re/C. This result indicates that there is a strong interaction be-
tween the two metals, changing the reducibility of both metal species.
CO chemisorption measurements were carried out for the reduced
Ru/C, Re/C, and RuRe/C catalysts, as shown in Table 2. Ru/C exhibited
the highest metal dispersion (55%), while Re/C showed the lowest
metal dispersion (32%). For the RuRe/C catalysts, the metal dispersion
was in the range of 39–42%, and it decreased with an increase in the
amount of added rhenium. TEM analyses were also conducted on the
RuRe/C (0.5) catalyst (Fig. S2). The TEM images show highly dispersed
metal particles (b2 nm in size) on the carbon support. Overall, the CO
chemisorption and TEM results suggest that Ru and Re particles in the
RuRe/C catalysts are well-dispersed on the carbon support.
CO chemisorption results of Ru/C, Re/C, and Ru–Re/C catalysts with Re/Ru atomic ratios of
0.25, 0.5, and 0.75.
Entry Catalyst Ru loading Re loading Re:Ru
Dispersion Particle size
(wt%)
(wt%)
(mol:mol) (%)a
(nm)a
1
2
3
4
5
RuRe/C
RuRe/C
RuRe/C
Ru/C
4
4
4
4
–
1.8
3.64
5.4
–
0.25
0.5
0.75
–
42.0
39.8
38.8
55.2
31.9
3.2
3.5
3.6
2.4
4.4
Re/C
3.64
–
a
Calculated from CO chemisorption measurements by assuming a stoichiometry of CO/
metalatom = 1.
dehydroxylation of cyclohexanol. Meanwhile, Ru/H-BEA showed a sig-
nificantly lower conversion of guaiacol (10%), and the major product
is 1-isopropoxy-2-methoxybenzene (77%). This result suggests that
Brønsted acids inhibit the CTH of guaiacol over Ru by catalyzing the un-
desired etherification of guaiacol and 2-propanol. Overall, it is difficult
to promote the dehydroxylation of guaiacol using an acidic support
under CTH conditions. Therefore, we explored the possibility of adding
oxophilic promoters to Ru/C to enhance the dehydroxylation activity.
In order to investigate the distribution of Ru and Re on the surface of
the carbon support, STEM-EDX analyses were carried out. Fig. 2 shows
STEM-EDX mapping images of the reduced Ru-Re/C (0.5) catalyst.
These images show that both Ru and Re atoms exist on the surface of
the carbon support and that they are evenly distributed on the support.
According to the phase diagram for a Ru—Re mixture, the two metals
are completely miscible due to their similar atomic sizes and surface en-
ergies. Thus, based on the EDX mapping and TPR results, it is believed
that Ru—Re bimetallic nanoparticles were formed in the RuRe/C cata-
lysts, resulting in strong interaction between Ru and Re.
3.2. CTH of guaiacol over RuRe/C catalysts
Bimetallic catalysts that consist of typical hydrogenation metals
(e.g., Ru, Rh) with more oxophilic metals (e.g., Re, Mo) have proven to
be effective for the hydrogenolysis of C—OH bonds for various bio-
mass-derived molecules. For examples, Tomishige et al. reported that
an addition of Re to Rh/SiO2 markedly enhances the hydrogenolysis ac-
tivity of glycerol to 1,3-propanediol [20–22]. Dumesic et al. reported
that Rh/C catalysts promoted with Re or Mo are highly active for the
hydrogenolysis of cyclic ethers (e.g., tetrahydrofurfuryl alcohol) to the
corresponding diols [23,24]. Accordingly, we prepared bimetallic RuRe
catalysts with different Re:Ru molar ratios for use in the CTH of guaiacol.
3.2.2. Catalytic activity of RuRe/C catalysts
Table 3 shows the catalysis results of the RuRe/C and Re/C catalysts
for the CTH of guaiacol at 473 and 513 K in 2-propanol as a solvent.
The results show that all of the RuRe/C catalysts are fairly active for
the CTH of guaiacol (70–99% conversion) and that they further convert
cyclohexanol to cyclohexane. The catalytic activity is a function of the
atomic ratio of Re to Ru in the catalysts. The TOF values for the conver-
sion of guaiacol and the cyclohexane selectivity decreased in the order
of RuRe/C (0.5) N RuRe/C (0.25) N RuRe/C (0.75). Also, the conversion
of 2-propanol showed the similar trend to the conversion of guaiacol,
indicating that the rate of 2-propanol dehydrogenation is an important
factor determining the activity in the CTH of guaiacol. Compared to the
RuRe/C catalysts, Re/C showed significantly lower activity for the CTH of
guaiacol (3.2% conversion), presumably due to the slower dehydroge-
nation rate of 2-propanol over Re/C. However, the major products
3.2.1. Characterization of RuRe/C catalysts
Fig. 1 shows the TPR profiles of the Ru/C, Re/C, and RuRe/C catalysts
with Re/Ru atomic ratios of 0.25, 0.5, and 0.75. The TPR curve for each
catalyst shows two major peaks: a sharp peak at 393–573 K and a
broad peak at 630–1000 K. The broad peak at 630–1000 K is related to
the reduction of the surface functional groups of the carbon support,
while the sharp peak at 393–573 K is related to the reduction of ruthe-
nium oxide and rhenium oxide. The peak temperatures of the Ru/C and
Re/C catalysts appear at 393 K and 573 K, respectively, and the RuRe/C
catalysts show a single reduction peak at 433–453 K, which is slightly
higher than that of Ru/C but much lower than that of Re/C. It was report-
ed that in the case of bimetallic catalysts containing noble metals such
Fig. 2. STEM-EDX images of the RuRe/C (0.5) catalyst.

116
Short communication
Table 3
Conversion and product selectivity for the CTH of guaiacol in 2-propanol at 473–513 K for 5 h with RuRe/C and Re/C catalysts.
Entry Catalyst Temp Conv. Sel. (%)
TOF
IPA Conv. Sel. (%) from IPA
(%)
(K)
(%)
(h−1
)
Cyclohexane Cyclohexanol 2-Methoxy cyclohexanol Phenol Others Ethers
Acetone Isopropyl ether
1
2
3
4
5
6
7
RuRe/C (0.25) 473
RuRe/C (0.5) 473
RuRe/C (0.75) 473
94.6
99.1
70.9
3.2
37.3
98.9
99.0
32.3
38.3
30.5
9.1
11.3
46.6
57.0
56.2
44.7
47.5
–
30.7
35.1
24.1
3.8
2.2
3.5
–
1.1
2.0
1.1
1.6
–
12.4
56.6
41.3
–
0.8
1.1
0.8
–
–
0.9
0.7
3.4
4.3
2.5
–
0.6
5.8
6.0
1377
2403
798
24
–
–
18.0
21.9
12.2
2.1
8.9
26.2
28.0
90.4
87.4
8.1
8.4
92.8
90.2
97.2
89.0
83.5
5.2
7.0
1.4
6.1
10.7
Re/C
Ru/C + Re/C
473
473
RuRe/C (0.25) 513
RuRe/C (0.5) 513
–
–
over Re/C were phenol (56.6%) and cyclohexane (9.1%), suggesting that
rhenium is active for the hydrogenolysis of C—OH bonds. Thus, the high
activity of RuRe/C catalysts for the production of cyclohexane can be ex-
plained by the enhanced hydrogenolysis activity over the Re surface
with the Ru-assisted dehydrogenation of 2-propanol. Higher tempera-
tures also promoted the hydrogenolysis of cyclohexanol over RuRe/C
catalysts. When the reaction temperature was increased from 473 K to
513 K, the cyclohexane selectivity was increased from 38% to 57% over
the RuRe/C (0.5) catalyst at 99% conversion.
The promoting effect of Re species on the hydrogenolysis of Ru/C
catalysts can be also explained by its acidic properties. Several re-
searchers suggested that Re promoted Ru/C or Rh/C catalysts have bi-
functional active sites composed of metal (for hydrogenation) and
acid sites (for dehydration), resulting in a bifunctional pathway for
C—O hydrogenolysis involving acid-catalyzed dehydration followed by
metal-catalyzed hydrogenation [23,27–29]. They reported that the acid-
ity of the catalysts originated from the presence of rhenium oxide spe-
cies in the catalysts. Accordingly, XPS analyses of the RuRe/C (0.5)
catalysts before and after reaction were carried out to check the pres-
ence of rhenium oxide species on the catalyst surface (see Fig. S3). The
XPS results showed that the surface rhenium species exist fully as rhe-
nium oxide (ReO3) in the fresh catalyst and remain as rhenium oxide
even after reaction at 473 K, although its oxidation state was slightly
changed, forming a mixture of ReO3 and Re2O7. Because the catalyst
was exposed to air after the reduction process, it is believed that rheni-
um oxide was formed in the reduced catalyst. Therefore, the XPS results
suggest that rhenium oxide in the RuRe/C catalysts can be the active
phase for the CTH of guaiacol.
markedly higher compared to Ru/C, indicating that the presence of Re
induces the surface acid sites (see Fig. S4). It is also interesting to note
that the acid site density on the RuRe/C catalyst was considerably higher
than the sum of individual acid site densities of Ru/C and Re/C. It appears
that there is a strong interaction (or coordination) between Ru and Re,
allowing for the generation of more acid sites than Re alone. Overall,
based on these observations, it is believed that the RuRe/C catalyst
exhibits bifunctional behavior in the CTH of guaiacol, in which Ru cata-
lyzes the dehydrogenation of 2-propanol and the hydrogenation-
hydrogenolysis of guaiacol and ReOx promotes cyclohexane production
via hydrogenolysis.
3.3. Reaction evolution
A typical reaction profile of the CTH of guaiacol at 473 K over RuRe/C
(0.25) is shown in Fig. 3. The conversion of guaiacol increased monoton-
ically throughout the reaction time, reaching 95% after 5 h. Phenol was
identified as the major product during the first hour of the reaction,
and it decreased with the reaction time. 2-Methoxycylohexanol and cy-
clohexanone were also observed, but the yields of both products were
low. Cyclohexanol and cyclohexane initially formed at 0.5 h and their
yields steadily increased throughout the reaction. The product evolution
for the decomposition of 2-propanol during the CTH of guaiacol was also
monitored (see Fig. S5). 2-Propanol was readily converted into acetone
and H2 along with a small amount of diisopropyl ether. Based on the
above results, the reaction network for the CTH of guaiacol over RuRe/
C is proposed (Fig. 4). Utilizing the hydrogen produced in-situ from 2-
propanol, guaiacol is initially converted into phenol through
demethoxylation and subsequently undergoes hydrogenation to
cyclohexanol. Cyclohexane is then produced by the hydrogenolysis of
cyclohexanol, which is a slow reaction over RuRe/C.
In order to characterize the presence of surface acid sites on the
RuRe/C (0.5) catalyst, NH3-TPD measurements were also carried out. It
was found that the acid site density on the Ru/C catalyst (0.2 mmol/g)
was similar to that on the activated carbon (0.2 mmol/g), implying
that the acidity of the Ru/C catalyst arises from the support. Meanwhile,
the acid site density on the RuRe/C (0.5) catalyst (0.8 mmol/g) was
4. Conclusions
In conclusion, we demonstrated an efficient route for the
hydrodeoxygenation of lignin monomer guaiacol via CTH using alcohols
as the source of hydrogen and RuRe/C as the catalyst. Ru showed activity
superior to those of Ni and Pd for the dehydrogenation of 2-propanol
and the hydrodeoxygenation of guaiacol to cyclohexanol (N70% yield).
Re promotion of the Ru/C catalysts further enhances the rate of C—O
hydrogenolysis, shifting the production distribution to cyclohexane
(~60% selectivity). Characterization of the catalysts by TPR, chemisorp-
tion, STEM/EDX, and NH3-TPD suggested that Ru—Re bimetallic nano-
particles were formed with surface acidity. The XPS results revealed
that rhenium exists as rhenium oxide on the surface of the RuRe/C cat-
alysts. The enhanced hydrogenolysis activity of the bimetallic RuRe/C
catalyst can be attributed to its bifunctional characteristic, by which
Ru catalyzes the hydrogenation-hydrogenolysis of guaiacol and ReOx
provides acid sites to promote the hydrogenolysis.
Acknowledgements
This work was supported by the New & Renewable Energy
Core Technology Program of the Korea Institute of Energy Technology
Fig. 3. Conversion of guaiacol and product yields as a function of reaction time at 473 K
with the RuRe/C (0.25) catalyst.

Short communication
117
Fig. 4. Reaction network of the CTH of guaiacol to cyclohexane using 2-propanol (isopropyl alcohol (IPA)) as a hydrogen donor and the RuRe/C catalyst. Compounds: 1-isopropoxy-2-
methoxybenzene (1), 1-isopropoxy-2-methoxy cyclohexane (2), isopropoxybenzene (3), isopropoxycyclohexane (4).
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Carbon-supported bimetallic Pd–Fe catalysts for vapor-phase hydrodeoxygenation
of guaiacol, J. Catal. 306 (2013) 47–57.
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Research Council of Science & Technology (NST) grant by the Korea gov-
ernment (MSIP) (No. CAP-11-04-KIST). The authors also appreciate fur-
ther support by the Korea Institute of Science and Technology (KIST)
Institutional Program (2E26550).
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