Aromatic hydrogenation of benzyl alcohol and its derivatives using compressed CO2/water as the solvent

Article abstract of DOI:10.1039/c2gc15999f

A green approach to the aromatic hydrogenation of benzyl alcohol and its derivatives to produce cyclohexanemethanol was demonstrated in this report. In this work, the hydrogenation reactions were carried using neat, CO ₂-expanded liquid (CXL), water and compressed CO₂/water, as the solvents. It was found out that using water as the solvent achieved the highest yield of the hydrogenation product (>96%). On the other hand, using the compressed CO₂/water system as the solvent significantly enhanced the reaction rate (only 1/5 of the reaction time needed for total conversion when compared to reactions in water) while still maintained high product yield (>90%). It is believed that CO₂ molecules dissolved in water could form carbonic acid simultaneously and the acid was proved to act as a promoter throughout the reaction. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2gc15999f

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PAPER
Aromatic hydrogenation of benzyl alcohol and its derivatives using
compressed CO /water as the solvent†
2
Hsin-Wei Lin, Clive H. Yen and Chung-Sung Tan*
Received 13th August 2011, Accepted 24th November 2011
DOI: 10.1039/c2gc15999f
A green approach to the aromatic hydrogenation of benzyl alcohol and its derivatives to produce
cyclohexanemethanol was demonstrated in this report. In this work, the hydrogenation reactions were
carried using neat, CO -expanded liquid (CXL), water and compressed CO /water, as the solvents. It was
2
2
found out that using water as the solvent achieved the highest yield of the hydrogenation product (>96%).
On the other hand, using the compressed CO /water system as the solvent significantly enhanced the
2
reaction rate (only 1/5 of the reaction time needed for total conversion when compared to reactions in
water) while still maintained high product yield (>90%). It is believed that CO molecules dissolved in
2
water could form carbonic acid simultaneously and the acid was proved to act as a promoter throughout
the reaction.
Introduction
solvents in chemical reactions, including hydrogenation, have
been explored in several studies. The advantages of using water
as the solvent are well known. In brief, water is a green and
abundant natural resource, which can be easily obtained.
Maegawa et al. reported the hydrogenation of a variety of aro-
matics, using transition-metal heterogeneous catalysts in water
under mild conditions. The results showed the possibilities of
aromatics hydrogenation in water, which were successfully
demonstrated by numerous examples. On the other hand, the
applications of SCF have gradually been the object of study over
the past few decades owing to the unique physical properties of
supercritical fluids, especially supercritical carbon dioxide
There are widespread applications of hydrogenated aromatic
compounds in day-to-day life. Aromatic hydrogenation is argu-
ably the most difficult type of hydrogenation due to the need to
overcome the high resonance energy of the benzene ring. To our
interest, cyclohexanemethanol, that can be made by hydrogen-
ation of benzyl alcohol, and its derivatives have been widely
5a
1
used as an intermediate in pharmaceutical drugs manufacturing.
Takagi et al. focused on the catalytic effects during the hydro-
genation of several benzyl compounds, which could easily
2
undergo hydrogenolysis reaction. Their results showed that the
yield of cyclohexanemethanol was 81% in ethanol at nearly
(
scCO ). Seki et al. reviewed the heterogeneous catalytic hydro-
2
6b
3
73 K, using Ru oxide as the catalyst. Furthermore, Nishimura
genation of organic compounds processed by SCF. In the
review paper and several other recent articles, a number of
examples of applying CO , including scCO and CO -expanded
and Hama reported the main hydrogenation products of benzyl
3
alcohol. Their research showed that Rh catalysts could have
2
2
2
been poisoned due to the formation of the byproduct, cyclo-
hexanecarboxaldehyde. However, this product was not observed
when using Pt catalysts. Until now, there is little information
regarding using green solvents for the aromatic hydrogenation
reactions. Nowadays, the use of organic solvents has been
seriously evaluated due to the principle of searching for green
liquid (CXL), as a substitute for conventional organic solvents
were listed. Comparing to the conventional organic solvents,
7
scCO is miscible with hydrogen gas, leading to a reduction of
2
the interfacial mass transfer resistance between gas and liquid. In
addition, scCO has long been considered as a green solvent
2
because of its non-toxic, non-flammable and environmental
friendly properties. Zhao and Arai’s groups had proposed the
4
solvents. Traditional organic solvents could have several draw-
backs that could not meet the modern day standards, such as
being volatile, flammable, explosive, harmful to the environment
and toxic to the human being. Therefore, it is necessary to find
out some alternative media that can avoid these shortcomings.
mechanism of the hydrogenation of nitro and nitroso compounds
8
in scCO and conventional solvents. One of their works showed
2
that using scCO as the solvent was more suitable than using
2
ethanol for the hydrogenation of chloronitrobenzene, due to
5
6
8b
Recently, water and supercritical fluids (SCF) and their uses as
the suppressing dehalogenation by the addition of CO2. In
addition, the feasibility of the hydrogenation of nitrobenzene
and its derivatives in compressed CO /water system was also
reported. Their latest study pointed out that using compressed
2
Department of Chemical Engineering, National Tsing Hua University,
No. 101Section 2Kuang-Fu Road, Hsinchu, 30013, Taiwan.
E-mail: cstan@mx.nthu.edu.tw
CO /water as the solvent was more efficient for the hydrogen-
2
8c
ation of nitrobenzene and chloronitrobenzene. In other research
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c2gc15999f
1
by Gao and Li, the addition of CO2 was influential to the
682 | Green Chem., 2012, 14, 682–687
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9
hydrogenation of nitrate ions in drinking water. Thus, to dis-
Table 1 Comparison of catalyst for hydrogenation of benzyl alcohol in
water
a
cover more extended examples of using green solvents for aro-
matic hydrogenation is the primary goal in this study. Therefore,
the superiority of several green solvents, including water, CXL
Product selectivity
(%)
and compressed CO /water was investigated for the hydrogen-
2
b
c
Entry Catalyst
Conv. (%)
43
2
3
4
5
Yield (%)
ation of benzyl alcohol and its derivatives. A self-synthesized
silica-supported Ru catalyst (Ru/MCM-41) using chemical fluid
deposition technique was selected in this study. A comparison in
catalyst efficiency between the self-synthesized Ru/MCM-41
catalyst and a commercial active carbon-supported Ru catalyst
1
2
Ru/C
4.4 0.7 0.1 94.8 40.8
1.5 0.2 2.3 96.0 82.6
Ru/MCM-41 86
a
2
Catalyst: 50 mg; solvent: water 50 g; benzyl alcohol: 1 g; H : 6 MPa;
b
temperature: 323 K; propeller stir: 1000 rpm; reaction time: 20 h. Ru/C
c
(Ru/C) was also made in this work.
metal loading: 5 wt%; Ru/MCM-41 metal loading: 3.7 wt%. Yield of
product 5 (cyclcohexanemethanol). The values are calculated by
multiplying the conversion with the product selectivity.
Results and discussion
Hydrogenation of benzyl alcohol
to achieve a higher selectivity of cyclohexanemethanol. It can be
seen that in entry 1 in Table 1, the selectivity of cyclohexane-
methanol was 94.8% at 323 K, which was significantly higher
Scheme 1 shows the reaction pathway of the benzyl alcohol
hydrogenation, which yielded toluene, methylcyclohexane,
cyclohexenemethanol and cyclohexanemethanol as the main pro-
ducts. Cyclohexenemethanol was detected by GC-MS. It is
speculated that 1-cyclohexene-1-methanol is the major com-
ponent of the three positional isomers of cyclohexenemethanol
since it is more stable than the other two isomers, 2-cyclohex-
ene-1-methanol and 3-cyclohexene-1-methanol. Moreover, an
undesirable byproduct, cyclohexanecarboxaldehyde, was always
detected less than 0.1% in this study and, therefore, neglected
during the product selectivity calculation. Table 1 shows the
comparison between Ru/C and Ru/MCM-41 in hydrogenation of
benzyl alcohol at 323 K. In order to obtain high selectivity of
cyclohexanemethanol, a complete reaction was preferred. In the
preliminary test, it was found out that the selectivity towards
toluene and methylcyclohexane was increased with increasing
reaction temperature. However, the selectivity of the fully hydro-
genated product cyclohexanemethanol was poor. Therefore, the
reaction temperature was adjusted to a lower temperature in order
2,3,10
than several reported values in the previous studies.
This
phenomenon may be explained by the less favored C—O bond
cleavage, also known as hydrogenolysis, during mild tempera-
ture condition. Therefore, instead of mainly producing toluene
and methylcyclohexane at high temperatures, the desired product
cyclohexanemethanol could be obtained in high selectivity at
mild temperatures. It was reported that lower reaction tempera-
ture and higher hydrogen pressure conditions were more suitable
11
for hydrogenation instead of hydrogenolysis. Accordingly, this
work was mainly focused on the mild temperature and high
pressure (323 K and 6 MPa H pressure). Besides, the yield of
2
cyclohexanemethanol was found to be greater when using Ru/
MCM-41 than using Ru/C in water solvent at 323 K (entry 2).
For Ru/MCM-41, the hydrophilic property on the silica support
surface may cause the catalyst to have a well-dispersion in water,
which is exactly opposite to the Ru/C catalyst, since the charcoal
surface is hydrophobic. This result has the same agreement with
12
our previous study in hydrogenation of bisphenol A. Therefore,
the Ru/MCM-41 catalyst was chosen as the catalyst to examine
the feasibility of other green solvents in the following sections.
The comparisons of different solvent systems and additives
for the hydrogenation of benzyl alcohol using Ru/MCM-41 as
the catalyst at 323 K are presented in Table 2. At first, the
influence of using water as the solvent was examined and the
results are shown in entries 1 and 2. The solubility of benzyl
alcohol in water is about 4 g per 100 ml at 298 K, in other
words, the saturation concentration of benzyl alcohol in water is
about 0.37 M at room temperature. Therefore, the amount of
benzyl alcohol used in the experiments was carefully selected
not to exceed the saturation amount. It was found that the yield
of cyclohexanemethanol was doubled while using water as the
solvent compared to neat at the reaction time of 20 h. This
confirms that the hydrophilic silica based catalyst is very suitable
12,13
for catalyzing reactions in water.
In addition, the results in
entries 3 and 4 also indicated a radical change when using com-
pressed CO /water as the solvent in hydrogenation of benzyl
2
alcohol. The results may suggest some benefits of the com-
pressed CO2 existence. Several positive factors such as the
increase of mass transfer and the decrease of viscosity of the
reactants might influence the reaction rate of benzyl alcohol
Scheme 1 Reaction pathway of the benzyl alcohol hydrogenation. 1:
benzyl alcohol, 2: toluene, 3: methylcyclohexane, 4: cyclohexenemetha-
nol, 5: cyclohexanemethanol.
6b
hydrogenation. Later on, a neat benzyl alcohol with the
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a
Table 2 Comparison of different solvent systems and additives used for the hydrogenation of benzyl alcohol
Product selectivity (%)
b
Entry
Solvent
Time (h)
Conv. (%)
2
3
4
5
Yield (%)
c
1
Neat
Water
Water
2
Water + CO (3 MPa)
Neat + scCO
Water + CO
Water + acetic acid
Water
20
20
1.5
1.5
5
5
5
50
86
38
53
25
98
93
100
6.0
1.5
1.8
2.7
3.4
2.5
5.8
0
3.0
0.2
0.7
0.8
0.9
4.8
16.4
3.5
9.7
2.3
8.8
8.4
12.9
0.5
1.0
0
81.3
96.0
88.7
88.1
82.8
92.2
76.8
96.5
40.6
82.6
33.7
46.7
20.7
90.4
71.4
96.5
2
3
4
5
6
7
8
d
2
(8 MPa)
(3 MPa)
2
e
28
a
b
Catalyst: 3.7 wt% of Ru/MCM-41 50 mg; solvent: water 50 g; benzyl alcohol: 1 g; H
2
: 6 MPa; temperature: 323 K; propeller stir: 1000 rpm. Yield
c
of product 5 (cyclcohexanemethanol). The values are calculated by multiplying the conversion with the product selectivity. Magnetic stir bar:
1
d
e
2
000 rpm. CO -expanded benzyl alcohol (CXL system). Acetic acid solution (0.01 M): 50 g.
addition of scCO was also tested and the result is shown in
explanation for the enhancement of the reaction rate might lie in
2
+
entry 5. Under the condition of 8 MPa of scCO , benzyl alcohol
that the proton, H , of acid or water could favor the cleavage of
2
17
was mostly expanded by CO instead of dissolving in it due to
a metal–carbon bond. In this circumstance, once the cyclo-
hexyl products were formed on the active sites of metal, the des-
orption rate may be enhanced in the presence of acid. Finally,
the highest yield of cyclohexanemethanol (96.5%) was found at
a reaction time of 28 h by using water as solvent (entry 8). This
result suggested that water is a suitable solvent for the hydrogen-
ation of benzyl alcohol to produce cyclohexanemethanol.
2
1
4
the low solubility of benzyl alcohol in CO2. Thus, the system
became a CXL system and the yield was only 1/4 of that of the
compressed CO /water system (entry 6). This result shows that
2
CO2 is a good additive for hydrogenation in water solvent
system. The main reason may be attributed to the changing of
acidity in the compressed CO /water system. According to the
2
literature, water is categorized as a Class I liquid, which cannot
be properly expanded by CO . Therefore, the properties of water
2
6
d
Hydrogenation of benzaldehyde
can be remained, with the exception of acidity. In this regard,
carbonic acid (H CO ) was formed when CO was dissolved in
2
3
2
Another example from the benzyl chemical family, benz-
aldehyde, was also tested for the hydrogenation reaction. Some
properties of benzaldehyde are quite similar to benzyl alcohol,
including molecular weight, melting point and solubility in
water. The entire hydrogenation of benzaldehyde can be con-
sidered as a series reaction. The carbonyl group (CvO) of benz-
aldehyde can be hydrogenated forming benzyl alcohol first,
followed by further hydrogenation, the major product cyclohexa-
nemethanol and the minor products toluene, methylcyclohexane
and cyclohexenemethanol can also be formed eventually
water, and the measured pH value dropped instantly from 6.2
DI water at 301 K) to 3.9 (CO -purged DI water at 301 K). The
(
2
pH value of 3 MPa CO compressed into water at 323 K was
2
reported to be about 3.4, and no significant change was observed
1
5
upon increasing the CO pressure to over 3 MPa. Namely, the
2
compressed CO /water system became a weak carbonic acid sol-
2
ution, which may directly increase the reaction rate of the aro-
matic hydrogenation of benzyl alcohol. To our interest, this
phenomenon is one that deserves empirical scrutiny. Therefore, a
simulated experiment of the carbonic acid-catalyzed effect was
inspected by adding another additive, acetic acid, into the
aqueous solution as the solvent. The pH value of 0.01 M acetic
acid solution was measured as 3.4 at 323 K. The result of using
acetic acid as the solvent is shown in entry 7. On comparison
(Scheme 2). The results of hydrogenation of benzaldehyde are
shown in Table 3. It was found that when using water as the
solvent, selectivity of cyclohexanemethanol could be achieved at
8
6.4% in 30 h (entry 3). When using compressed CO /water, the
2
yield of cyclohexanemethanol was increased nearly 6 times
(entry 4 compare to entry 1) and 2 times (entry 5 compare to
entry 2) at reaction times of 5 h and 10 h, respectively. Further-
more, entry 5 was observed with the highest yield of cyclohexa-
nemethanol using only 1/3 of the reaction time than in water
with compressed CO /water (entry 6), the yield of the fully
2
hydrogenated product cyclohexanemethanol decreased. It was
found that both the compressed CO /water and the acetic acid
2
had the ability to increase the reaction rate. From the literature,
Takagi et al. had reported that adding lower relative permittivity
(
entry 3). The improvement of using the compressed CO /water
2
(dielectric constant) of carboxylic acids (acetic acid, butyric acid,
and lauric acid) into various organic solvents, the conversions of
hydrogenation reactions were increased due to the decrease in
1
0
relative permittivity of the mixture solutions. Unfortunately,
the ratio of the hydrogenolysis products also rose in their study
(increased by 20%). It is known that if an acid exists in the
system, especially strong acid, the elimination reaction would be
promoted due to the possible protonation of the hydroxyl
group. However, in the present study, this phenomenon was
restricted by the mild operating condition. Another possible
Scheme 2 Reaction pathway of benzaldehyde hydrogenation. 1: benzyl
alcohol, 2: toluene, 3: methylcyclohexane, 4: cyclohexenemethanol, 5:
cyclohexanemethanol.
16
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a
Table 3 Hydrogenation of benzaldehyde
Product selectivity (%)
b
Entry
Solvent
Time (h)
Conv. (%)
1
2
3
4
5
Yield (%)
1
2
3
4
5
Water
Water
Water
Water + CO
Water + CO
5
99
91.5
51.4
5.8
52.5
5.9
0.5
0.1
0
1.3
1.1
1.8
0
0
4.9
0.6
3.8
5.4
0.8
2.7
2.9
2.0
0
7.2
7.1
10
30
5
10
10
100
100
100
100
100
45.8
86.4
43.6
89.2
82.6
45.8
86.4
43.6
89.2
82.6
2
2
(3 MPa)
(3 MPa)
c
6
Water + acetic acid
9.8
0.4
a
b
Catalyst: 3.7 wt% of Ru/MCM-41: 50 mg; solvent: water 50 g; benzaldehyde: 1 g; H
2
: 6 MPa; temperature: 323 K; propeller stir: 1000 rpm. Yield
c
of product 5 (cyclcohexanemethanol). The values are calculated by multiplying the conversion with the product selectivity. Acetic acid solution
0.01 M): 50 g.
(
a
Table 4 Hydrogenation of benzoic acid
Entry
Solvent
Time (h)
Conv. (%)
1
2
3
Water
Water + CO (3 MPa)
2
Water + acetic acid
2
2
2
100
70
100
b
Scheme 3 Hydrogenation of benzoic acid.
a
Catalyst: 2.7 wt% of Ru/MCM-41, 25 mg; solvent: water, 100 g;
: 6 MPa; temperature: 323 K; propeller stir:
benzoic acid: 0.25 g; H
1000 rpm. Acetic acid solution (0.01 M): 50 g.
2
b
system for hydrogenating benzaldehyde was not as extreme as
for hydrogenating benzyl alcohol. This result may due to the fact
that the hydrogenation of benzaldehyde is a series reaction. It is
speculated that the acid had little or no effect on the first step of
the process (Scheme 2), in which the carbonyl group (CvO) is
reduced to a hydroxyl group (C–OH). In addition, entry 6 also
shows the verification of acid-catalyzed effect in hydrogenation
of benzaldehyde when using acetic acid solution as the solvent.
The result was expected and confirmed to be nearly identical
value of the system may promote the hydrogenolysis reaction
since the elimination of the functional group could be catalyzed
by acid. As a result, the reaction rate greatly enhanced and the
selectivity for the hydrogenolysis products slightly increased.
However, this is not the case for the hydrogenation of benzoic
acid since the carboxylic protonation of benzoic acid can only be
processed in strong acidic condition. Much to our surprise, the
conversion of the benzoic acid hydrogenation somewhat fol-
lowed a different trend, which actually decreased when adding
with the compressed CO /water system (entry 5).
2
Hydrogenation of benzoic acid
CO into the reaction system. A reasonable explanation could be
2
provided here as that a dilution effect could occur when adding
In addition, a third compound, benzoic acid, was also chosen for
the testing in this study. Although it is expected that benzoic acid
should be difficult to convert into cyclohexanemethanol by
gaseous hydrogen, the corresponding product cyclohexanecar-
boxylic acid, however, is still a valuable compound to synthesize
for pharmaceutical application (Scheme 3). It is also noteworthy
to point out an unexpected discovery from our experiment.
Table 4 shows the results in the hydrogenation of benzoic acid.
19
CO into the reaction systems. When the compressed CO was
2
2
added into the gas phase, the mole fraction of hydrogen in the
gas phase was decreased. This dilution effect of compressed CO
2
9c
1
would reduce the gas-to-liquid mass transfer rate of hydrogen.
This phenomenon is relatively common when using scCO for
2
hydrogenation reactions and it may also occur in our experimen-
tal systems. According to the experimental data, the promotion
effect should be more dominant than the dilution effect when
When using compressed CO /water as the solvent, the reaction
2
adding CO into the reaction system when hydrogenating benzyl
rate of benzoic acid decreased. From the experimental results, it
2
alcohol and benzaldehyde and vice versa when hydrogenating
benzoic acid. Furthermore, when using 0.01 M acetic acid sol-
ution as the solvent, no positive or negative influence was found
since no promotion or dilution effect was expected in the system.
is reasonable to assume that the pK value of the reactants might
a
also affect the reaction. Since the pH value of the saturated sol-
ution of benzoic acid is already about 3, the compressed CO2
would not be able to alter the acidic condition. On the other
hand, the pH value of the saturated solution of benzyl alcohol
and benzaldehyde are both neutral. Therefore, the addition of the
2
Advantages of CO as the promoter
compressed CO could provide a weak acidic environment for
2
the hydrogenation reaction to take place. In addition, it is specu-
lated that protonation of the hydroxyl group could occur in the
weak acidic environment (in our case, pH around 3). The pro-
tonated hydroxyl group could manipulate the electron density of
the total compound causing a lowering of activation energy for
the aromatic ring hydrogenation. Moreover, lowering the pH
The comparison between CO and an organic acid as a hydro-
genation promoter is discussed below. Since CO2 is gaseous
under standard condition for temperature and pressure, the reac-
2
1
8
tion products (excluding gaseous) and CO could be easily sep-
2
arated by depressurization right after the reaction. The remaining
liquid waste is therefore less contaminated and could be easily
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processed for disposal or recycling. However, when using an
organic acid as a promoter, the residual acid could be a problem
since the side product ester could be formed in the reaction with
(hold for 5 min). The products, toluene [HPLC-grade 99.9%,
Echo], methylcyclohexane [HPLC-grade 99.9%, Echo], cyclo-
hexanemethanol [99%, Sigma–Aldrich], cyclohexanecarboxylic
acid [98%, Sigma–Aldrich] were used as the standard in the
analysis.
alcohol. On the other hand, when comparing CO to inorganic
2
acids (mineral acids), CO2 is less toxic and environmental
friendly, which could provide a greener operation. Therefore,
using compressed CO /water in the hydrogenation of benzyl
2
alcohol and its derivatives could prevent these serious problems.
In addition, the possible reverse water gas shift reaction which
could produce a catalyst poison CO, should not be a critical
issue in this study. The relatively mild reaction conditions and
Conclusions
In conclusion, five key points in the formation of cyclohexane-
methanol by hydrogenation of benzyl alcohol and its derivatives
were successfully demonstrated in this work. It can be summar-
ized as the following: (i) the yield of cyclohexanemethanol when
using the self-synthesized Ru/MCM-41 catalyst was found to be
nearly 2 fold higher than that when using a commercial carbon
supported catalyst in water; (ii) high conversion and product
selectivity from the hydrogenation reactions of benzyl alcohol
and benzaldehyde can be achieved in water at mild temperatures;
the biphasic environment of compressed CO /water could help
2
2
0
avoid catalyst poisoning.
Experimental
Catalyst preparation
(
iii) after examining several green alternative solvents, a pro-
Self-synthesized silica-supported Ru catalysts were prepared
motion effect was discovered when using the compressed carbon
dioxide into water solvent system; (iv) water is a suitable solvent
for the ring hydrogenation of aromatic compounds; (v) the com-
pressed CO /water system could be very efficient for ring hydro-
genation of aromatic alcohols and aldehydes. Last but not least,
applying the idea of compressed CO /water for hydrogenation
reactions can be considered as an inspiring example for green
and sustainable chemistry.
by chemical fluid deposition techniques and followed by the
1
2,21
previously described experiments.
The metal precursors
including bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(1,5-cyclo-
2
octadiene)ruthenium [Ru(cod)(thmd) , Strem] and ruthenium
2
acetylacetonate [Ru(acac) , Strem] and the silica support
3
2
MCM-41 (SiO , Sigma-Aldrich) were all used as received. In a
2
typical trial, 285 mg of MCM-41 and ca. 87 mg of Ru(cod)
(
thmd) were added together into a high pressure cell leading to
2
a maximum metal ratio of 5% by weight. At 423 K, 10 MPa of
H and 10 MPa of CO were premixed in a gas reservoir and
injected into the cell for a reaction of 2 h. After the reaction, the
2
2
Acknowledgements
cell was depressurized and flushed with CO for a few times to
2
The authors would like to acknowledge the assistance from
Mr. T. D. Phan for the catalyst characterization. This work was
supported by the National Science Council of ROC (NSC 96-
eliminate the unreacted metal precursors. The remaining powder
sample was then collected for further analysis and catalytic
testing. The metal loading of the catalysts were analyzed by
energy dispersive X-ray spectroscopy (JEOL JSM-5600/Oxford
2
628-E-007-125-MY3) and the Ministry of Economic Affairs of
ROC (97-EC-17-A-09-S1-022).
6
587). The other catalyst properties and recycling procedures are
provided in the supplementary information.
Notes and references
Hydrogenation of aromatic compounds
1 E. Xue, H. Pan, Z. Pan and J. Zhang, Fine Chem. Intermed., 2006, 36,
2
1.
2 Y. Takagi, T. Naito and S. Nishimura, Bull. Chem. Soc. Jpn., 1964, 37,
85.
The experiments for the hydrogenation of benzyl alcohol and its
derivatives were implemented in a semi-batch autoclave. Benzyl
alcohol [99%, Sigma–Aldrich], benzaldehyde [99%, Alfa
Aesar], benzoic acid [99%, Sigma–Aldrich], ruthenium on acti-
vated carbon [5% Ru/C, Sigma–Aldrich] and acetic acid [100%,
Merck] were all used as received. In a typical trial, a mixture of
5
3
4
5
S. Nishimura and M. Hama, Bull. Chem. Soc. Jpn., 1966, 39, 2467.
P. G. Jessop, Green Chem., 2011, 13, 1391.
(a) T. Maegawa, A. Akashi, K. Yaguchi, Y. Iwasaki, M. Shigetsura,
Y. Monguchi and H. Sajiki, Chem.–Eur. J., 2009, 15, 6953; (b) L. Song,
X. Li, H. Wang, H. Wu and P. Wu, Catal. Lett., 2009, 133, 63;
(c) N. Yan, C. Xiao and Y. Kou, Coord. Chem. Rev., 2010, 254, 1179.
5
0 mg of the catalyst, 1 g of the benzyl alcohol and 50 g of de-
6
7
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2
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