Graphene-Modified Ru Nanocatalyst for Low-Temperature Hydrogenation of Carbonyl Groups

Article abstract of DOI:10.1021/acscatal.5b02170

Low-temperature efficient hydrogenation of C=O bonds in various compounds, which is one of the most important processes for producing fuels and chemicals, is of fundamental interest but remains a significant challenge. The primary problem is a lack of heterogeneous catalyst systems that are highly active at ambient or low temperatures. This paper describes an efficient strategy for designing a low-temperature hydrogenation catalyst. Ru nanoparticles supported on reduced graphene oxide (Ru/RGO) show remarkable efficiency for hydrogenation of levulinic acid into γ-valerolactone at temperatures as low as -10 °C. The catalyst is also highly active toward low-temperature hydrogenation of C=O bonds in other carbonyl compounds into C-OH bonds, such as furfural, propionaldehyde, 2-pentanone, hydroxyacetone, acetone, acetophenone, cyclohexanone, and benzophenone. X-ray photoelectron spectroscopy and in situ Fourier transform infrared demonstrate that the electron transfer between Ru⁰ and RGO leads to the formation of an electron-rich state of Ru⁰ nanoparticles that are highly effective for activating C=O bonds.

Full text of DOI:10.1021/acscatal.5b02170

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Article
Graphene-modified Ru nanocatalyst for low-
temperature hydrogenation of carbonyl groups
Jingjing Tan, Jinglei Cui, Xiaojing Cui, Tiansheng Deng, Xianqing Li, Yulei Zhu, and Yong-Wang Li
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.5b02170 • Publication Date (Web): 05 Nov 2015
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ACS Catalysis
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Grapheneꢀmodified Ru nanocatalyst for lowꢀtemperature hydroꢀ
genation of carbonyl groups
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Jingjing Tan, †,‡ Jinglei Cui, †,‡ Xiaojing Cui, † Tiansheng Deng, † Xianqing Li, § Yulei Zhu*,†,
§, Yongwang Li †,§
†
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan
030001, P. R. China.
University of Chinese Academy of Sciences, Beijing 100049, P.R. China.
Synfuels China Co. Ltd, Beijing, 101407, P.R. China.
‡
§
ABSTRACT: Low-temperature efficient hydrogenation of C=O bonds in various compounds, which is one of the most
important processes for producing fuels and chemicals, is of fundamental interest but remains a significant challenge. The
primary problem is lacking of heterogeneous catalyst systems which are high active at ambient or low temperatures. This
paper describes an efficient strategy for designing low-temperature hydrogenation catalyst. Ru nanoparticles supported
on reduced graphene oxide (Ru/RGO) show remarkable efficiency for hydrogenation of levulinic acid into γ-valerolactone
o
at temperatures as low as -10 C. The catalyst is also highly active towards low-temperature hydrogenation of C=O bonds
in other carbonyl compounds into C-OH bonds, such as furfural, propionaldehyde, 2-pentanone, hydroxyacetone, ace-
tone, acetophenone, cyclohexanone and benzophenone. XPS and in situ FT-IR demonstrate that the electron transfer be-
tween Ru0 and RGO leads to the formation of electron-rich state of Ru0 nanoparticles that are highly effective for activat-
ing C=O bonds.
KEYWORDS: Graphene; hydrogenation; low-temperatrue; levulinic acid; γ-valerolactone; water
1. Introduction
bridization between graphene sp2-states and the dsp-
states of metal nanoparticles, favoring the electron feed-
back between graphene sheet and metal sites. Such an
electron feedback is demonstrated to promote the aver-
aged d-band center of the metal particle shifting towards
its Fermi level28-32. Based on the above understandings, we
hypothesize that in the catalysis process, such a shift
would ease the electron transferring between the metal
sites and the reactant molecules, suggesting a superior
catalytic activity.
The efficient hydrogenation or oxidation at ambient
and lower temperatures on heterogeneous metal catalysts
is highly desirable but challenging. This problem can be
tackled through the development of efficient catalyst sys-
tems, especially the design of active metal sites. The pri-
mary strategies include the application of noble metals
that are naturally effective at low temperatures, the re-
duction of metal dimension to subnano or atomic levels1-5,
the modification of chemistry of metal centers by lig-
ands6-8, and the morphology control for exposing specific
metal plane(s)9-13. In addition, it is a common and conven-
ient method for supported metal catalysts to modify the
properties of supports to produce highly active metal
OH
OH
O
O
H2O/H+
metal/H2
O
O
HO
O
HO
O
OH
OH
O
OH
n
crystals14-17
.
cellulose
γꢀvalerolactone
levulinic acid
Scheme 1 Reaction pathways from biomass to GVL
Since its discovery, graphene has attracted increasing
attentions. It is a two-dimensional single-layer sheet of
graphite with π-electrons fully delocalized on the graphit-
ic plane18-23. It also has the unusual ballistic electron
transport, anomalous integer quantum Hall effect at room
temperature and fractional quantum Hall effect at low
temperatures24-27. The unique electronic properties of
graphene suggest its great potential as a new carbon sup-
port for modifying the structure and chemistry of metal
nanoparticles. Recent studies have demonstrated that the
two-dimensional structure of graphene facilitates the hy-
As one of the key catalytic processes in the biomass
utilization, the hydrogenation of biomass-derived levulin-
ic acid (LA) that is a versatile and renewable platform
molecule primarily produced from cellulose33-35, into γ-
valerolactone (GVL) has attracted many attentions
(Scheme 1)36. Many catalyst systems, including non-noble
metals (Cu-, Ni- and Co) and noble metals (Pt, Pd, Ru)
supported catalysts, have been reported to catalyze the
hydrogenation of LA into GVL efficiently37-44. However,
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lyst which has been demonstrated to be effective for LA hy-
drogenation at 70 oC was also tested 44a. However, its activity
Table 1 Hydrogenation of levulinic acid catalyzed by vari-
1
2
ous catalysts a
o
is much lower at 40 C. This result suggests the higher effi-
3
4
5
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7
8
9
ciency of Ru/RGO catalyst for low-temperature hydrogena-
tion of LA. The catalytic performances of Ru/RGO were fur-
LA
conv.%
GVL
select.%
Entry
Cat.
T/oC
t/h
o
o
ther investigated at lower temperatures (30 C and 20 C)
(Table 1 and Figure S1). Ru/RGO displays high activities at
1
Ru/RGO
Graphiteb
GOb
40
40
40
40
40
40
40
30
20
0
100
0
99.9
-
2
o
o
2
2
ambient temperatures (30 C and 20 C), whereas a signifi-
cant decrease in the activity was found for Ru/AC (Figure S1).
The Ru/AC catalyst is unable to catalyze LA hydrogenation
3
0
-
2
4
5
RGOb
1.2
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
-
2
o
when the reaction temperature was lowered to -10 C. Sur-
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Ru/Graphite
Ru/AC
16.2
55.8
28.8
100
100
93.2
3.2
70.6
0
2
prisingly, the Ru/RGO catalyst shows considerable activity at
o
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7
2
-10 C, which are, to date, not reported in the literature con-
cerning heterogeneous metal-catalyzed hydrogenation pro-
cesses. These results show that the Ru/RGO catalyst has a
superior ability to catalyze the hydrogenation of LA at low
temperatures.
Ru/TiO2
Ru/RGO
Ru/RGO
Ru/RGO
Ru/AC
2
8
9
10
11
12
13
5
8
12
12
12
12
The turnover frequencies (TOF) and the apparent activa-
tion energies (Ea) over Ru/RGO and Ru/AC catalysts were
investigated for better understanding the intrinsic activities
of these two catalysts (Table 2, Figures S4-S7). The TOF val-
ues over Ru/RGO are 3-5 times those over Ru/AC, and Ea
over Ru/RGO is lower than that over Ru/AC. This result
clearly demonstrates the higher intrinsic activity of Ru/RGO.
In particular, the Ea value on Ru/RGO is close to that on
highly active homogeneous catalysts (61 kJ /mol) 45, indicat-
ing the unique talent of graphene as the support for enhanc-
ing the activity of Ru catalyst.
Moreover, several typical carbonyl compounds were cho-
sen, and their hydrogenation performances on Ru/RGO cata-
lyst were investigated (Table 3). Notably, the Ru/RGO cata-
lyst is highly active for the hydrogenation of C=O bond in
these aldehydes and ketones under mild temperatures. These
0
Ru/RGO
Ru/AC
-10
-10
a: Reduction condition: 150 oC, 4 MPa H2, 2 h, in the presence of
14.94 g water, in the Teflon-lined steel autoclave vessel; Reac-
tion condition: LA (2 g，17.2 mmol), 15 g mixture of 2 wt%
Ru/support catalyst and water (60 mg 2 wt% Ru/support); H2,
4 MPa; : 15 g mixture of catalyst and water (60 mg catalyst).
The carbon balance for each run exceeded 96%. The LA solu-
tion did not freeze at the temperature of -10 oC for 24 h.
b
drastic reaction conditions are required to obtain high
GVL yield over non-noble catalysts. Furthermore, the
metal leaching in liquid acid media for these catalysts,
especially Cu catalysts, leads to the deactivation of cata-
lysts. In contrast, noble metal supported catalysts, partic-
ularly Ru supported catalyst, displayed higher catalytic
efficiency and better stability in the aqueous hydrogena-
tion of carbonyl groups. The optimal temperature win-
Table 2 The calculated reaction rate constants and appar-
ent activation energies over various catalysts a
Cat.
T/ oC
k/ h-1
TOF/ h-1
Ea (kJ /mol)
2112.2b
dows for LA hydrogenation are above 70 C8, 38-43. In this
o
20
30
40
0.3711
paper, reduced graphene oxide (RGO) was chosen as the
support to modify the hydrogenation activity of Ru cata-
lysts. Ru/RGO exhibits superior activity and selectivity in
the low-temperatures hydrogenation of LA (as low as -10
oC) and other carbonyl compounds.
Ru/RGO
66.01
0.9852
2.0926
4656.3c
5520.2d
20
30
40
0.0340
0.1194
0.3384
532.7e
996.8f
1866.5g
2. Results and discussion
Ru/AC
87.66
61± 2
Initially, Ru/RGO catalyst, GO, RGO, graphite and
Ru/graphite were tested for the hydrogenation of LA (11.8
wt%) in water at 40 C. LA was completely converted and a
o
nearly 100% selectivity toward GVL was obtained over
Ru/RGO within 2 h. (Table 1 entry1 and Figure S1). In contrast,
graphite and GO were inactive towards LA hydrogenation
(entries 2-3), while a negligible conversion of LA was ob-
served with RGO as the catalyst (entry 4). Therefore, the Ru
sites account for the catalytic hydrogenation performance. A
low conversion of LA was obtained when graphite as the
support (entry 5). Besides, active carbon (AC) was chosen as
a representative carbon support, and Ru/AC catalyst has sim-
ilar distribution of surface oxygenic functional groups to that
of Ru/RGO (Figure S2 and Table S1). The Ru/AC catalyst ap-
pears lower activity than Ru/RGO catalyst. The Ru/TiO2 cata-
Ru–TPPTSh 70
-
-
a: LA (2 g，17.2 mmol), 15 g mixture of 2 wt% Ru/support
catalyst and water (60 mg 2 wt% Ru/support); H2 4 MPa.
The number of active Ru sites for TOF calculation was
b
determined by CO pulse chemisorption. : t=30 min, con-
c
d
version= 40.1%; : t=15 min, conversion= 44.2% : t=15 min,
e
f
conversion= 52.4% : t=30 min, conversion= 10.9%; : t=15
g
h
min, conversion= 10.2% : t=15 min, conversion= 19.1%
:
Ref. 45. The effect of H2 on the conversion of LA was listed
in Figure S3
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Table 3 Hydrogenation of different carbonyl compounds over Ru/RGO catalyst a
1
2
3
4
Entry
reactant
product
Conv.%
Select.%
T/ oC
t/h
TOF/ h-1
5
6
7
1
96.6
92.8
99.9
99.8
20
20
4
4
137c
191c
2
8
9
3b
4b
70.1
92.3
99.8
99.9
60
40
3
1
365d
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17
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19
20
21
22
6102d
5b
6b
7b
8b
96.1
100
100
100
99.9
96.8e
99.9
85.6f
40
40
40
40
1.5
1
3371d
2897d
8296d
4735d
1
1
Reaction conditions: a: 0.2 g substrate, H2 0.5 MPa, 9.8 g mixture of 2 wt% Ru/RGO and water (60 mg 2 wt% Ru/RGO), b: 1 g
substrate, 8 g ethanol; H2 4 MPa, 2%Ru/RGO 60 mg; c: t=30min d: 2 g substrate, 8 g ethanol; H2 4 MPa, 2 wt% Ru/RGO 60
mg t=20 min; e and f: the total selectivity of the two products. The carbon balance for each run exceeds 95%.
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aldehydes and ketones were converted to their correspond-
ing alcohols with high efficiency. In particular, the TOF val-
ues for the hydrogenation of furfural, acetophenone, benzo-
phenone and acetone over Ru/RGO are much higher than
those over heterogeneous catalysts reported in the litera-
ture46-49. Therefore, the Ru/RGO catalyst shows great poten-
tial as an effective and versatile catalyst for low-temperature
hydrogenation of carbonyl compounds.
indicated by XRD, the diffraction peaks of Ru nanoparticles
in Ru/RGO were not detected, indicating that the particle
size of Ru were below the XRD detection line (3-5 nm) (Fig-
ure S8A-d). TEM and HRTEM results imply the formation of
uniformly dispersed Ru nanoparticles with an average diame-
ter of 2.0 nm (Figure S10 a-d).
The structural evolution of graphene during the reduction
was also investigated by Raman spectra. The integrated in-
tensity ratio of D band (1350 cm-1) to G band (1580 cm-1)
(ID/IG) are demonstrated to present the disorder of graphene
53-54. After the same reduction process, the calculated ID/IG
ratio of Ru/RGO (1.39) is larger than that of RGO (1.18) (Fig-
ure S11). This enhancement in the ID/IG ratio is indicative of
the presence of carbon vacancies and defects that were
XRD, XPS, TEM and High-resolution TEM (HRTEM) were
carried out to understand the effect of graphene support on
the structure of Ru. The diffraction peak (002) of raw graph-
ite at 26.5o disappeared after oxidation into GO (Figure S8A-
b). This result indicates that the oxidation process led to the
formation of few-layer graphene structure and the introduc-
tion of plenty oxygenic functional groups on the layers. The-
se surface functional groups, as indicated by XPS results (Fig.
S9a and Table S1), include C-O (hydroxyl/ epoxy), C=O (car-
bonyl) and O-C=O (carboxyl) (286.5, 287.4 eV and 288.5 re-
spectively)50-51. They are reported to be anchoring sites for
metal complexes52. To verify which oxygenated functional
groups are anchoring sites for Ru, Ru/RGO and RGO were
analyzed by XPS (Figure S2a and Figure S9b). For RGO, the
peak associated with C-C bond (centered at 284.6 eV) be-
came predominant while the peaks of oxygenated groups
(hydroxyl, epoxy, carbonyl and carboxyl) decreased tremen-
dously compared with GO. This result suggested that most of
the oxygenated groups have been removed during the reduc-
tion process (Figure S9c). For Ru/RGO, the intensities of the
oxygenic functional groups were further decreased compared
with RGO (Table S1). In particular, the amounts of C-O and
C=O decreased obviously compared with RGO. Hence, the C-
O and C=O groups are primarily the anchoring sites for Ru
species. This result is in accordance with the literature52.
These functional groups promoted the dispersion of Ru. As
Figure 1 The XPS Ru0 regions of Ru supported catalyst. (a)
Ru/RGO (b)Ru/TiO2 (c) Ru/AC
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phene. The structures of Ru nanoparticles on AC were also
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investigated by HRTEM and XRD (Figure S13). HRTEM and
XRD results in this work and in our latest work indicate that
Ru nanoparticles on AC and TiO2 supports 43, 44a have similar
size distribution (around 2.0 nm) and expose the same
planes (002 and 100 planes) with those on graphene. It is
therefore likely that the significantly higher low-temperature
activity of Ru/RGO is due to the electron-rich state of Ru0
NPs on graphene.
To further understand the origin of the higher low-
temperature activity of Ru/RGO catalyst, the activation be-
haviors of C=O bond on Ru/RGO, Ru/TiO2 and Ru/AC cata-
lyst were characterized by in situ Fourier-transform infrared
spectroscopy (FT-IR). Acetone was chosen as the probe mo-
lecular, and the FT-IR spectra were recorded under room
temperature. For acetone, the peak appearing at 1740 cm-1
region is ascribed to C=O stretching vibration (Figure 2a)57. A
red shift in the wavenumber of C=O stretching vibration
peak occurred in three Ru supported catalysts. Surprisingly,
the red shift for Ru/RGO catalyst (142 cm-1 Figure 2d) is much
larger than that for Ru/TiO2 (27 cm-1 Figure 2b) and Ru/AC
catalysts (44 cm-1 Figure 2c). The red shift of C=O bond can
be interpreted as the increase in the backbonding from Ru d
orbital into the C=O 2π* antibonding orbital, leading to
weakness in the strength of C=O bond. This result confirms
apparently that the activation of C=O bonds are more effec-
tive on Ru/RGO catalyst. The highly effective activation of
C=O bonds on Ru/RGO likely results from that the electron-
rich state of Ru0 NPs on graphene promotes the electron
transfer from Ru0 d orbital to C=O 2π* antibonding orbital.
The stability of the Ru/RGO catalyst was investigated by
four consecutive catalytic runs at different LA conversion
levels (Figure 3). GVL yield are sustained on multiple reuse.
The possible Ru leaching during the reaction was also de-
tected. As the loss of Ru is usually more severe at higher
temperatures, we analyzed the amount of Ru in the solution
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Figure 2 In situ FTIR of (a) acetone, (b) adsorbed on
Ru/TiO2, (c) adsorbed on Ru/AC, (d) adsorbed on Ru/RGO
at ambient temperature.
formed during the chemical reduction of GO55,56. Hence, the
increased ID/IG ratio in Ru/RGO indicates that the reduction
of GO was promoted in the presence of Ru, leading to the
formation of more defects in RGO. As confirmed by HRTEM
the Ru nanoparticles reduce the aggregation and restacking
of graphene in the reduction process (Figure S10, a, e and f)52.
This inhabitation effect of Ru on the aggregation of RGO was
further verified by the BET results. As shown in Table S2, the
SBET of RGO is smaller than that of Ru/RGO.
More importantly, the XPS results of the reduced Ru cata-
lysts provide basic clues concerning the interaction between
support and Ru. Ru/RGO, Ru/AC and Ru/TiO2 were chosen
for the XPS characterization because of their obvious differ-
ence in the low-temperature activities. The overlapping of
the Ru3d3/2 XPS signals with the main signal of C1s allows
the study of metallic Ru only via the Ru3d5/2 XPS signal.
Dumesic et al. have reported that the temperature exceeded
o
by ICP-OES and by a reaction test at 40 C (detailed in sup-
porting information). No Ru was detected, reflecting that the
possible leaching of Ru is below the detection limit (1 μg Ru
/L solution). Furthermore, the Ru nanoparticles size of spent
catalyst increased slightly from 2.0 nm to 2.5 nm (Figure S14).
The above results demonstrate the excellent stability and
reusability of Ru/RGO catalyst.
o
140 C is enough for reducing the supported Ru-carbon cata-
lyst 41. To clarify whether the three catalysts are fully reduced
o
at 150 C 4 MPa H2, the LA hydrogenation performances and
XPS spectra of the three Ru supported catalysts reduced at
o
150, 200 and 250 C were investigated respectively (The re-
duction processes are detailed in S1.2 Method part in ESI).
For each catalyst, the activities for LA hydrogenation were at
the same level (Table S3), and the binding energy (BE) values
of Ru0 nanoparticles were nearly the same at the three reduc-
tion temperatures (Figure 1, Figure S12). This result indicates
o
that the temperature of 150 C is sufficient for the reduction
of Ru species on the three supports (RGO, AC and TiO2). An
interesting feature is the negative correlation between the BE
values of Ru0 and low-temperature activities. As shown in
Figure 1, the BE value of Ru0 nanoparticles on graphene is the
lowest (280.50 eV), followed by those on AC (280.75 eV) and
TiO2 (280.81 eV), while Ru/RGO shows the highest low-
temperature activity, followed by Ru/AC and Ru/TiO2 (Table
1). As the BE value indicates the electron density of Ru0, this
result suggests the electron-rich state of Ru0 NPs on gra-
Figure 3 Stability of the Ru/RGO catalyst. Reaction condi-
tions: LA (2 g，17.2 mmol), 15 g mixture of 2 wt% Ru/RGO
catalyst and water (60 mg 2 wt% Ru/RGO) ; H2 4 MPa.
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3. Conclusion
taining RuCl3•3H2O at room temperature for 24 h, respec-
o
1
2
3
4
tively, then dried at 100 C for 20 h. Ru/TiO2 catalyst was
calcined in air at 400 oC for 4 h, while Ru/AC and
In conclusion, the Ru/RGO catalyst exhibits remarkable effi-
ciency for low-temperature hydrogenation of LA into GVL.
GVL was obtained efficiently over the catalyst with a high
yield of 99.9% and a TOF of 2112.2 h-1 at room temperature
o
Ru/Graphite were calcined in N2 at 400 C for 4 h. Prior to
the reactions, these catalysts were moved to an autoclave and
reduced at 150 °C in 4 MPa of hydrogen for 2 h in the pres-
ence of water.
5
o
(20 C). The value of Ea for LA hydrogenation over Ru/RGO
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7
8
9
is 66.01 kJ/mol, which is equivalently to that over highly ac-
tive homogeneous Ru-TPPTS catalyst (61 kJ/mol). The hy-
drogenation of LA can be efficiently performed at -10 C on
the catalyst. Moreover, the catalyst is also highly active to-
wards the selective hydrogenation of C=O bonds of other
carbonyl compounds into C-OH bonds. The high efficiency
of the catalyst could be attributed to that the electron trans-
ferring between Ru0 and RGO leads to the formation of elec-
tron-rich state of Ru0 nanoparticles that are demonstrated to
be highly active towards the activation of C=O bonds.
4.4 Catalyst testing. All experiments were performed in a
batch reactor with a magnetic stirring. Typically, LA (2 g, 17.2
mmol) was added into the Teflon-lined steel autoclave vessel
with 60 mg reduced Ru catalyst and 14.94 g water. Before
each run the vessel was sealed and flushed with H2 to ex-
clude air for five times. After reactions, the vessel was cooled
down/warmed up to room temperature by water. The reac-
tion products were centrifuged for 10 min and then filtrated
to obtain clear solution. The samples were analyzed by a GC
(Agilent 7890) equipped with an AB-INNOWAX capillary
column (30m×0.32mm×0.5μm). Standard solutions were
used to obtain the calibration curves to calculate concentra-
tions of the compounds by the external standard method.
The catalyst was recycled as described by the following pro-
cedure. At the end of the hydrogenation run, the catalyst was
separated from the reaction mixture by high rate of centrifu-
gation, thoroughly washed with water three times to remove
the adsorbed species, and then reused as the catalyst for the
next run under the identical conditions. The Ru content in
the remained reaction solution was analyzed by ICP-OES
(PerkinElmer Optima 2100 DV).
o
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4. Experiment Section
4.1 Graphene oxide (GO) synthesis. GO was synthesized
from graphite powder by the Hummers and Offemann’s
method 58. Typically, Graphite powder (4 g) and NaNO3 (2 g)
were mixed with H2SO4 (92 mL, 98%) under magnetic stir-
o
ring at 0 C for 1 h. KMnO4 (12 g) was added slowly to the
mixture with vigorous stirring at 10 oC. The mixture was
transferred to a water bath of 35 oC for 0.5 h followed by add-
ing a certain amount of distilled water (184 mL). The temper-
ature of the diluted suspension was raised to 98 oC and main-
tained for 1 h. The suspension was further diluted to 460 mL
with warm water, followed by the addition of 30% H2O2
aqueous solution (40 mL). Finally, the obtained solution was
filtered and washed with HCl (1 mol/L) and distilled water,
respectively. The resulting solid was dried and dissolved with
water. The prepared suspension was ultrasonicated under 40
KHz for 60 min and centrifugated at 4000 rpm for 30 min to
obtain stable collosol of GO. The collosol of GO was dried at
ambient temperature to obtain power of GO.
4.5 Catalyst characterizations. The catalyst characteriza-
tions are detailed in the electronic supporting information,
which include (X-ray diffraction (XRD) Transmission elec-
tron microscope (TEM), high-resolution transmission elec-
tron microscope (HRTEM), X-ray photoelectron spectrosco-
py (XPS), BET, CO pulse chemisorption, Raman spectrosco-
py, and in situ FTIR.
ASSOCIATED CONTENT
4.2 Synthesis of Ru/RGO. Ru/RGO heterogeneous catalyst
was synthesized through a hydrothermal method with hy-
drogen. Typically, 720 mg of as-prepared GO was dispersed
into 120 mL water solution and ultrasonicated under 40 KHz
for 3 h. Then 9.8 mL of as-prepared GO aqueous solution and
1.20 ml RuCl3•3H2O (CRu3+ =1.0 mg/ml) were added into a
vessel, followed by ultrasonication for 3 h. The mixture was
then stirred at room temperature overnight. Afterwards, the
mixture was transferred into a Teflon-lined steel autoclave
and maintained at 150 oC and 4.0 MPa H2 for 2 h to co-reduce
the GO and Ru3+, followed by cooling down to reaction tem-
perature. The effect of Cl- on the activity of Ru/RGO was
investigated (Table S5). A certain amount of HCl (2 times the
mole of Cl- ions in RuCl3•3H2O applied for the preparation of
Ru/RGO) was added into the mixture of Ru/RGO, levulinic
acid and water prior to the reaction. The changes in the con-
version were negligible after the addition of Cl-, indicating
that Cl- ions did not affect the activity of Ru/RGO.
Supporting Information. Experimental details, Table S1-S5,
Figure S1 to S14 can be found in Supporting Information. This
material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* E-mail: zhuyulei@sxicc.ac.cn (Y. Zhu). Tel.: +86 351 7117097;
Fax: +86 351 7560668.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
The authors gratefully acknowledge the financial support of
the Major State Basic Research Development Program of
China (973 Program) (no. 2012CB215305)
4.3 Preparation of Ru/AC, Ru/TiO2 and Ru/Graphite. The
catalysts were prepared by the wet impregnation method.
The support of active carbon, TiO2 and Graphite were dried
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The high efficiency of graphene-modified Ru nanocatalyst for low-temperature hydrogenation of
C=O bonds originates from the electron transfer between Ru0 and graphene.
8
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