RuCu nanoparticles supported on graphene: A highly efficient catalyst for hydrolysis of ammonia borane

Article abstract of DOI:10.1016/j.jallcom.2013.12.134

Well dispersed RuCu nanoparticles (NPs) supported on graphene were in situ synthesized by a one-step co-reduction of aqueous solution of ruthenium (III) chloride, cupric (II) chloride, and graphite oxide (GO) with ammonia borane (AB) under ambient condition. The nature of the NPs was fully characterized by TEM, HRTEM, XRD, energy dispersive spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The as-synthesized NPs exhibit much higher catalytic activity for hydrolytic dehydrogenation of AB than the monometallic Ru and Cu, bimetallic RuCu/graphene reduced by NaBH₄, and graphene free RuCu counterparts. Additionally, the as-synthesized NPs supported on graphene exhibit higher catalytic activity than the catalysts with other conventional supports, such as SiO₂, γ-Al₂O₃, and carbon black. The activity of Ru₁Cu_7.5/graphene NPs in terms of turnover frequency (TOF) is 135 mol H₂ min^-1 (mol Ru) ^-1, which is higher than Ru/graphene, and most reported Ru-based or other noble metal-based NPs for the catalytic hydrolysis of AB. The activation energy for hydrolysis of AB in the presence of Ru₁Cu _7.5/graphene NPs was determined as 30.59 kJ mol^-1, which is lower than most of the reported catalysts. Furthermore, the as-prepared NPs exert satisfied durable stability for the hydrolytic dehydrogenation of AB.

Full text of DOI:10.1016/j.jallcom.2013.12.134

Journal of Alloys and Compounds 590 (2014) 241–246
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
RuCu nanoparticles supported on graphene: A highly efficient catalyst
for hydrolysis of ammonia borane
a
a
a,b,
⇑
, Gongzhen Cheng a,
⇑
Nan Cao , Kai Hu , Wei Luo
a
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, PR China
Suzhou Institute of Wuhan University, Suzhou, Jiangsu, 215123, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 October 2013
Received in revised form 12 December 2013
Accepted 12 December 2013
Available online 21 December 2013
Well dispersed RuCu nanoparticles (NPs) supported on graphene were in situ synthesized by a one-step
co-reduction of aqueous solution of ruthenium (III) chloride, cupric (II) chloride, and graphite oxide (GO)
with ammonia borane (AB) under ambient condition. The nature of the NPs was fully characterized by
TEM, HRTEM, XRD, energy dispersive spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS).
The as-synthesized NPs exhibit much higher catalytic activity for hydrolytic dehydrogenation of AB than
the monometallic Ru and Cu, bimetallic RuCu/graphene reduced by NaBH
terparts. Additionally, the as-synthesized NPs supported on graphene exhibit higher catalytic activity
than the catalysts with other conventional supports, such as SiO -Al , and carbon black. The activity
of Ru Cu7.5/graphene NPs in terms of turnover frequency (TOF) is 135 mol H
higher than Ru/graphene, and most reported Ru-based or other noble metal-based NPs for the catalytic
hydrolysis of AB. The activation energy for hydrolysis of AB in the presence of Ru Cu7.5/graphene NPs
was determined as 30.59 kJ mol , which is lower than most of the reported catalysts. Furthermore,
the as-prepared NPs exert satisfied durable stability for the hydrolytic dehydrogenation of AB.
Ó 2013 Elsevier B.V. All rights reserved.
4
, and graphene free RuCu coun-
Keywords:
Nanoparticles
Graphene
Hydrogen storage
Ammonia borane
2
,
c
2 3
O
ꢀ1
ꢀ1
1
2
min (mol Ru) , which is
1
ꢀ1
1
. Introduction
numerous opportunities for modulating the electronic structures
of the catalysts and improving their catalytic activity. Ru nanopar-
Ammonia borane (H
3
N–BH
3
, AB) complex is considered to be
ticles, including monometallic Ru-based NPs [16] and bimetallic
RuCo [17], and RuNi [18] NPs, have showed extremely high activ-
ities for catalytic dehydrogenation of AB. However, the catalytic
activity of Cu-based NPs are still not satisfactory, especially when
the Cu is the dominant content of the NPs [19–21]. Therefore,
developing a facile one-step route to construct the RuCu NPs with
high catalytic activities is highly desirable.
the most promising candidate for portable hydrogen applications
among all other practical hydrogen storage materials due to its
high hydrogen content (19.6% wt), high stability under ambient
condition, and environmentally benignity [1–7]. More importantly,
it is able to release hydrogen via a room-temperature hydrolysis
reaction with a suitable catalyst, which appears to be the most
convenient one for portable hydrogen storage application [8–15].
In its complete hydrolysis reaction, one mole of AB complex can
In recent years, nanostructured carbon materials, such as car-
bon nanotubes (CNT) [22], carbon nanofibers (CNF) [23], and
graphene nanosheets [24] have been extensively studied as the
suitable substrate to grow active NPs and harvest their catalytic
2
generate three moles of hydrogen (H ) according to Eq. (1).
2
catalyst
!
activity. In particular, graphene, a single-atom thick of sp honey-
NH
3
ꢀ BH
3
þ 2H
2
O
NH
4
BO
2
þ 3H
2
ð1Þ
comb carbon lattice has received considerable attention as a cata-
lyst support due to their outstanding charge carrier mobility,
mechanical robustness, large surface area, as well as their thermal
and chemical stability [25–29]. It has been reported that the en-
hanced catalytic activity of the graphene supported metal NPs is
mainly caused by the charge transfer across the graphene–metal
interface, due to the graphene–metal spacing and Fermi lever dif-
ference [30–32].
So far, not only noble and non-noble metal NPs but also their
composites were tested for hydrolytic dehydrogenation of AB.
The noble metal-based NPs have been identified to be effective
for catalytic hydrolysis of AB, however, their high price and limited
abundance hinder their practical application. Therefore, it is prom-
ising to alloy a parent noble metal with a second non-noble metal
to minimize the usage of noble metals. Furthermore, it could offer
Herein, we report the in situ synthesis of graphene supported
RuCu alloy NPs using AB as reductant in a one-step co-reduction
route at room temperature under ambient atmosphere. The as-
⇑
Corresponding authors at: College of Chemistry and Molecular Sciences, Wuhan
University, Wuhan, Hubei 430072, PR China. Tel.: +86 2787467716.
E-mail addresses: wluo@whu.edu.cn (W. Luo), gzcheng@whu.edu.cn (G. Cheng).
0
925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jallcom.2013.12.134

2
42
N. Cao et al. / Journal of Alloys and Compounds 590 (2014) 241–246
synthesized NPs exhibit superior catalytic activities than the
monometallic Ru, Cu NPs and graphene-free RuCu counterparts.
3. Results and discussion
3.1. Synthesis and characterization
2
. Experimental
In a typical synthesis, the graphene supported RuCu/graphene
NPs were prepared by adding AB into the precursor solution con-
taining RuCl , CuCl , and graphene oxide (GO) at room tempera-
2
.1. Materials
3
3
2
+
2+
Ammonia borane (NH
3
–BH
3
, AB, Aldrich, 90%), sodium borohydride (Sinopharm
ꢁnH O,
The Wuhan Xinsirui Technology Co., Ltd., P99.9%), cupric chloride dihydrate
ture. The Ru and Cu were reduced together to produce alloy
structured NPs during the reduction process due to the similarity
Chemical Reagent Co., Ltd., P96%), Ruthenium (III) chloride hydrate (RuCl
3
2
0
2+
in redox potentials of the two metal precursors (E (Cu
/
(
CuCl
Triquo Chemical Co., Ltd.), neutral silica power (SiO
-Al , Sinopharm Chemical Reagent
Co., Ltd., FCP), potassium permanganate (KMnO Shanghai Chemic Co., Ltd.,
P99.5%), hydrogen peroxide (H Sinopharm Chemical Reagent Co., Ltd.,
P30%), sodium nitrate (NaNO , Sinopharm Chemical Reagent Co., Ltd., P99%), sul-
furic acid (H SO
, Sinopharm Chemical Reagent Co., Ltd., 95ꢂ98%), tetrahydrofuran
O, Sinopharm Chemical Reagent Co., Ltd., P99%), dimethyl ether anhydrous
10O, Sinopharm Chemical Reagent Co., Ltd., P99.7%), graphite power (Sinop-
2
ꢁ2H
2
O, Sinopharm Chemical Reagent Co., Ltd., P99%), Ketjenblack EC-300 J
(
2
, Branch of Qingdao Haiyang
Chemical Co., Ltd.). Aluminum oxide neutral (
c
2 3
O
4
,
2 2
O ,
3
2
4
(
(
C
C
4
H
H
8
4
harm Chemical Reagent Co., Ltd., P99.85%). All chemicals were used as obtained.
We use ordinary distilled water as the reaction solvent.
2.2. Graphene oxide (GO) preparation
Graphene oxide (GO) was synthesized using a modified Hummer’s method [33–
4].
3
2.3. In situ synthesis of RuCu/graphene catalysts and their catalytic studies of hydrolytic
dehydrogenation of AB
In a typical experiment, 8 mg GO were dissolved in 2.6 mL of water kept in a
two-necked round-bottom flask. Ultrasonication was required to get a uniform dis-
persion. 1 mL ruthenium chloride solution (0.01 mol/L) and 1 mL cupric chloride
solution (0.01 mol/L) was added into this flask. One neck was connected to a gas
burette, and the other was connected to a pressure-equalization to introduce AB.
(e)
C
O
4
mL of solution containing 62 mg AB(90%) were kept in the pressure-equalization.
The reactions were started when the AB solution was added to flask with vigorous
stirring, the evolution of gas was monitored using the gas burette. After the hydro-
gen generation reaction was completed, 2 mL of solution containing 30.8 mg AB
was added to the flask to study the catalytic activity of the as-synthesized NPs. A
water bath was used to control the temperature of the reaction solution. By chang-
Cu
Cu
3
+
2+
ing the precursor ratio between Ru and Cu , the RuCu alloy NPs of different com-
positions were prepared. For comparison, the RuCu catalyst without GO reduced by
AB, the RuCu/graphene reduced by NaBH
duced by AB were synthesized using the similar method.
4 2 3 2
, RuCu/C, RuCu/c-Al O and RuCu/SiO re-
Ru
2.4. Catalytic hydrolysis of AB
0
200
400
600
800
1000
binding energy / eV
Sets of experiments with different concentration of RuCu (0.017, 0.0225, 0.034,
0
.0425 mmol) were performed at room temperature (25 ± 0.2 °C) while the AB con-
Fig. 1. (a and b). TEM image of the Ru
1
Cu7.5/graphene with different magnifications.
centration was kept the same (1 mmol) to determine the rate law of the catalytic
hydrolysis of AB. Temperature was varied at 25 ± 0.2 °C, 30 ± 0.2 °C, 35 ± 0.2 °C
and 40 ± 0.2 °C while the concentration of Ru (0.010 mmol) and AB (1 mmol) were
kept constant to obtain the activation energy (Ea).
(
c and d). TEM image of the Ru Cu7.5/graphene after the fifth cycle with different
1
1
magnifications. (e) EDX spectrum of Ru Cu7.5/graphene.
2.5. Stability test
Ru/graphene
Cu/graphene
Ru(002)
For stability test, catalytic reactions were repeated 5 times by adding another
equivalent of AB (1 mmol) into the mixture after the previous cycle.
Cu(111)
2.6. Characterization
Transmission electron microscope (TEM) and energy-dispersive X-ray spectros-
RuCu/graphene
GO(001)
copy (EDS) images were obtained using a FEI Tecnai G20 U-Twin TEM instrument
operating at 200 kV. Powder X-ray diffraction (XRD) patterns were measured by a
Bruker D8-Advance X-ray diffractometer using Cu Ka radiation source
ꢀ
1
(
k = 0.154178 nm) with a velocity of 6 deg min . FTIR spectra were collected at
GO
room temperature by using a Thermo FTIR-iS10 instrument using KBr discs in the
ꢀ
1
4
00–4000 cm region. Raman spectra were carried out using a confocal Raman
microscope (Renishaw, RM-1000) at 514.5 nm excitation. X-ray photoelectron spec-
10
20
30
40
50
60
troscopy (XPS) measurement was performed with
spectrophotometer.
a Kratos XSAM 800
Fig. 2. XRD patterns of GO, Ru/graphene, Cu/graphene and RuCu/graphene.

N. Cao et al. / Journal of Alloys and Compounds 590 (2014) 241–246
243
D
G
RuCu/graphene
RuCu/graphene
GO
G
D
GO
8
00
1000
1200
1400
1600
-1
1800
2000
2200
4
000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber/cm
Raman shift / cm
Fig. 3. FTIR spectra of GO and RuCu/graphene.
Fig. 4. Raman spectra of GO and RuCu/graphene.
Cu) = +0.34 eV vs. SHE; E (Ru3+/Ru) = +0.40 eV vs. SHE). The micro-
structure of RuCu/graphene NPs was fully analyzed by TEM, energy
dispersive X-ray spectrometry (EDS), and high resolution TEM
0
both the Ru(002) crystal plane (0.214 nm) and the Cu(111) plane
0.208 nm), demonstrating the crystalline nature of RuCu alloy
NPs. Fig. 2 shows the power XRD pattern of the as-prepared
RuCu/graphene NPs. The as-synthesized NPs have a very weak
peak intensity because of their small size. The diffraction peak
(
(
HRTEM) observations. As shown in Fig. 1a, the NPs were well dis-
persed on graphene, which help to prevent the agglomeration. In
Fig. 1b, the d-spacing of the NPs is ꢂ0.210 nm, which differs from
(
b)
Raw
Raw
(
a)
Fit
Fit
Background
Background
sp2
2
-
-
-
-
C
-
-
-
-
sp C
C-O
C-O
C=O
COO
C=O
COO
2
90
288
286
284
282
290
288
286
284
282
280
Binding energy (eV)
Binding energy (eV)
Raw
(
d)
(
c)
Raw
Fit
Fit
Background
Cu 2p
Background
Ru 3p
Cu 2p
RuO
2
3p
CuO 2p
CuO 2p
4
68 467 466 465 464 463 462 461 460
Binding energy (eV)
965 960 955 950 945 940 935 930 925
Binding energy (eV)
(
e)
C 1s + Ru 3d
O 1s
Cu 2p
Ru 3p
1
000
800
600
400
200
0
Binding energy (eV)
Fig. 5. XPS spectra of C 1s peaks of GO(a) and RuCu/graphene(b), Ru 3p peaks(c) and Cu 2p peaks(d) of RuCu/graphene) and the survey scan(e).

2
44
N. Cao et al. / Journal of Alloys and Compounds 590 (2014) 241–246
3
2
2
1
1
0
0
.0
.5
.0
.5
.0
.5
.0
3.0
2.5
Ru Cu
AB(with GO)
SB(with GO)
AB(with C black)
AB(with SiO2)
1
2.5
2.0
Ru Cu5
1
Ru Cu
1.5
1
7.5
10
Ru Cu
AB(with γ−Al O )
1
2
3
1.0
AB(without GO)
GO
Ru Cu
1
12.5
Ru (0.004 mmol)
Cu (0.03 mmol)
0.5
0.0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28
time (min)
0
2
4
6
8
10 12 14 16 18 20 22 24 26
time (min)
Fig. 7. Time plots of catalytic dehydrogenation of AB over the Ru
1
Cu7.5/graphene,
respectively; and Ru Cu7.5
2 3
O NPs reduced by AB and GO under ambient
Fig. 6. Time plots of catalytic dehydrogenation of AB over the RuCu/graphene
catalysts at ambient condition. Ru/AB = 0.004 (molar ratio).
Ru
Ru
1
Cu7.5/graphene NPs reduced by AB and NaBH
Cu7.5/SiO and Ru Cu7.5 -Al
4
1
,
1
2
1
/
c
conditions. Ru/AB = 0.004.
around 42.9° is between the typical reflections of hcp-structured
Ru(002) (42.2°) and fcc-structured Cu(111) (43.3°), indicating that
RuCu is formed as an alloy and not as a core–shell structure. This is
similar with Cheng’s results on their NiPt systems [35]. Further-
more, the most intense peak at around 8.4° corresponds to the
GO disappeared, and new peak at around 23.2° is observed in the
as-prepared graphene supported NPs, indicating that the GO is suc-
cessfully reduced to graphene. In the Raman spectroscopy (Fig. 3),
the GO and graphene supported NPs exhibit two peaks centered at
containing functional groups (such as ACAO, AC@O, ACOO) in
RuCu/graphene (Fig. 5b) decrease significantly [21], which also re-
veal the reduction of GO. However, the overlap of the C 1s and Ru
3d peaks around 285 eV makes it difficult to analyze this range for
ruthenium correctly (Fig. 5e). Therefore, as the peak of Ru 3p of the
catalysts shown in Fig. 5c, the Ru 3p feature fits well to two peaks
at 461.4 and 463.5 eV, readily assigned to the Ru(0) 3p and Ru(IV)
3p, respectively [36]. Fig. 10d shows the peak of Cu 2p. There are
four peaks whose peak tops were 933.1, 952.9, 933.6 and
953.6 eV, which stand for Cu(0) and Cu(II). The formation of
ꢀ1
1
354 and 1596 cm , corresponding to the D and G bands of the
carbon products, respectively. The intensity ratio of the D to G
band (I /I ) is generally accepted to reflect the degree of graphiti-
zation of carbonaceous materials and defect density. After loading
of the RuCu NPs, the I /I of GO is increased from 1.02 to 1.41. The
2
RuO and CuO most likely occurs during the sample preparation.
D
G
D
G
3.2. Catalytic activities for hydrolysis of AB by Ru
1
Cu7.5/graphene NPs
relative changes in the D to G peak intensity ratio confirm the
reduction of GO during the in situ fabrication. Fig. 4 shows the FTIR
spectra of GO and graphene supported RuCu alloy NPs. It can be
Without Ru, the Cu NPs show no activity toward catalytic
hydrolysis of AB as shown in Fig. 6. When pure Ru NPs were sup-
ported on graphene, keeping the molar ratio of Ru/AB as 0.004,
AB cannot be catalytic decomposed completely, and only 89% of
ꢀ1
seen clearly that the disappearance of C@O peak at 1634 cm
,
ꢀ1
ꢀ1
CAOH peak at 1227 cm and the CAO peak at 1057 cm of GO
after the formation of graphene supported core–shell NPs, further
indicating the GO was reduced to graphene during the process.
Furthermore, X-ray photoelectron spectroscopy (XPS) was used
to investigate the as-synthesized RuCu/graphene NPs. Compared
with the peaks of GO (Fig. 5a), the intensities of the oxygen
H
2
is released for about 1 h. When the Cu/Ru molar ratio is 7.5,
the release of H can be completed in about 9 min, indicating the
2
positive effect of between Ru and Cu on the hydrolysis of AB. Fur-
ther increased the Cu/Ru molar ratio to 10 and 12.5 results in no
significant decrease of the reaction time, indicating the best Cu/
Table 1
Catalytic activity of different noble metal-based catalysts used for the hydrolytic dehydrogenation of AB.
mol 1 M min ) M = Pt, Ru, Pd, Au
ꢀ
ꢀ1
Ea (kJ mol
ꢀ1
)
Ref.
Catalyst
TOF (mol H
2
Ru/C
Ru(0)@MWCNT
Pt@MIL-101
Ni0.74Ru0.26 alloy NPs
RuCu/graphene
Ni@Ru
429.5
329
233.22
194.8
135
34.81
33
40.7
37.18
30.39
44
40
41
42
18
This study
43
114
Ag@CoNi/graphene
Ag@Co/graphene
Ru/graphene
103
102.4
100
83.3
77.0
75
36.15
20.03
11.7
46
49.56
47
37
38
16
44
38
36
Ru@Al
2
O
3
after acetic acid treatment
Ag@Ni/graphene
laurate-stabilized ruthenium(0) nanoclusters
Ru@Al
Au/Co/Fe core–shell
Co35Pd65/C
2
O
3
39.6
37.2
34.9
32.9
23.05
16.4
6.25
48
–
27.5
47
67
44
45
46
17
47
17
48
RuCo (1:1)/
Ru/ -Al
c
-Al
2
O
3
c
2
O
3
RuCu (1:1)/
RGO/Pd
c
-Al
2
O
3
52
51

N. Cao et al. / Journal of Alloys and Compounds 590 (2014) 241–246
245
3
2
2
2
.0
.8
.6
.4
(
a) 3.0
(b)
2
2
1
1
0
0
.5
.0
.5
.0
.5
.0
ln rate=1.11 ln[Cat]+6.25
0.017 mmol
.0225 mmol
0.034 mmol
.0425 mmol
0
2.2
2
1
.0
.8
0
1.6
0
2
4
6
8
10 12 14 16 18 20 22
time (min)
-4.2 -4.0 -3.8 -3.6 -3.4 -3.2 -3.0
lnc
Fig. 8. (a) mol H
hydrogen generation rate versus the concentration of Ru
2
/mol AB versus time graph for the Ru
1
Cu7.5/graphene catalytic hydrolysis of AB for different Ru
Cu7.5/graphene NPs. (both in logarithmic scale).
1
Cu7.5/graphene concentration at 25 ± 0.2 °C; (b) the plot of
1
Ru molar ratio in the RuCu alloy NPs is 7.5. The activity in terms of
turnover frequency (TOF) is 135 (mol H min (mol Ru) ) for this
2
as-synthesized NPs, which is higher than Ru/graphene [16], and
most reported Ru-based or other noble metal-based NPs for the
catalytic hydrolysis of AB, if the TOF is normalized in terms of
mol noble metal (Table 1).
and GO has no catalytic activity toward hydrolysis of AB, highlight-
ing graphene as the dominant factor in facilitating hydrolysis of AB
in our system and the cooperative effect between graphene and
RuCu NPs for AB dehydrogenation.
Fig. 8 shows the plots of hydrogen generation from the hydroly-
1
sis of AB solution in the presence of different Ru Cu7.5/graphene
ꢀ1
ꢀ1
For comparison, when stronger reducing agent NaBH
4
is em-
NPs concentrations at 25 ± 0.2 °C. The initial rate of hydrogen gen-
eration was determined from the initial nearly linear portion of
each plot. The line slope of the plot of hydrogen evolution rate ver-
sus catalyst concentration in a log–log scale is 1.11, indicating that
ployed instead, as shown in Fig. 7, the catalytic activity of the
RuCu/graphene NPs is inferior to that of RuCu/graphene NPs re-
duced by AB. As the classical Lewis acid-based adducts, ammonia
borane have weaker reducibility over the traditionally reducing
agents like sodium borohydride, resulting in the slower kinetics
and better control over the NPs formation and further affecting
their catalytic activity [16,37,38]. Additionally, to study the effects
of the supported materials on the catalytic performances of the as-
the hydrolysis of AB catalyzed by Ru
der with respect to the catalyst concentration.
In order to get the activation energy (E ) of the AB hydrolysis
catalyzed by Ru Cu7.5/graphene NPs, the hydrolytic reactions were
1
Cu7.5/graphene NPs is first or-
a
1
carried out at different temperatures, with the range of 25–40 °C.
The values of rate constant k at different temperatures were calcu-
lated from the slope of the linear part of each plot from Fig. 9a. The
Arrhenius plot of lnk vs. 1/T for the catalyst is plotted in Fig. 9b,
from which the apparent activation energy was determined to be
synthesized alloy NPs, Ru
and graphene-free Ru Cu7.5 are prepared and their catalytic activ-
ities toward hydrolysis of AB are studied. As shown in Fig. 7, their
1 2 1 2 3 1
Cu7.5/SiO , Ru Cu7.5/c-Al O , Ru Cu7.5/C
1
catalytic activities are all inferior to that of Ru
1
Cu7.5/graphene NPs,
(
a)3.0
(b) 1
1.4
lnk=-3679.4(1/T)+23.15
2
2
1
1
0
0
.5
.0
.5
.0
.5
.0
11.3
1.2
11.1
o
T=25
T=30
T=35
T=40
C
C
C
C
1
Activation Energy
o
o
o
-1
Ea=30.59 kJ mol
1
1
1
1.0
0.9
0.8
0
2
4
6
8
10
0
.00320
0.00325
0.00330
0.00335
time (min)
1/T
Fig. 9. (a) mol H
reciprocal absolute temperature, 1/T (K )).
2
/mol AB versus time graph for the Ru Cu7.5/graphene catalytic hydrolysis of AB at different temperatures, Ru/AB = 0.004; (b) the Arrhenius plot (ln k vs. the
1
ꢀ
1
(
a)3.0
100
(b)
2
2
1
1
0
0
.5
.0
.5
.0
.5
.0
8
6
4
0
0
0
1
2
3
st
nd
rd
4th
th
5
20
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26
time (min)
1
2
3
4
5
Run
Fig. 10. (a). Time plots of catalytic dehydrogenation of AB over the Ru
1
Cu7.5/graphene catalysts from 1st to 5th cycles at 25 ± 0.2 °C. Ru/AB = 0.004; (b). Percentage of initial
catalytic activity of Ru Cu7.5/graphene in successive runs after the reuse for the hydrolysis of AB.
1

2
46
N. Cao et al. / Journal of Alloys and Compounds 590 (2014) 241–246
approximately 30.59 kJ mol 1, being lower than most of the re-
ꢀ
[3] W.Q. Qin, C.R. Yang, X.H. Ma, S.S. Lai, J. Alloys Comp. 509 (2011) 338–342.
[
4] A. Gutowska, L. Li, Y. Shin, C.M. Wang, X.S. Li, J.C. Linehan, R.S. Smith, B.D. Kay,
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