Hydrothermal Preparation of a Robust Boehmite-Supported N,N-Dimethyldodecylamine N-Oxide-Capped Cobalt and Palladium Catalyst for the Facile Utilization of Formic Acid as a Hydrogen Source

Article abstract of DOI:10.1002/cctc.201500161

Bimetallic CoPd nanoparticles (NPs) on boehmite (AlOOH) were synthesized under hydrothermal conditions using three different capping agents for the facile utilization of formic acid (FA) as a hydrogen source. The CoPd NPs capped with N,N-dimethyldodecylamine N-oxide (DDAO) supported on AlOOH (CoPd-DDAO/AlOOH) exhibited superior catalysis and recyclability in the hydrogenation of maleic anhydride (MAn) in water without metal leaching. The formation of monodispersed CoPd-DDAO NPs on AlOOH that contained both cobalt oxides and CoPd alloy in each NP was indicated by TEM with energy-dispersive spectroscopy, XRD, and X-ray absorption spectroscopy (XAS) studies. X-ray photoelectron spectroscopy and XAS supported the partial electron transfer phenomenon in CoPd-DDAO NPs. The as-prepared CoPd-DDAO/AlOOH catalyst showed activity for the utilization of FA formed in situ from biomass for the hydrogenation of MAn. It suggested that the DDAO capping agent contributed strongly to the favorable electronic/geometric changes in CoPd alloy for the facile utilization of FA.

Full text of DOI:10.1002/cctc.201500161

DOI: 10.1002/cctc.201500161
Full Papers
Hydrothermal Preparation of a Robust Boehmite-
Supported N,N-Dimethyldodecylamine N-Oxide-Capped
Cobalt and Palladium Catalyst for the Facile Utilization of
Formic Acid as a Hydrogen Source
[
a]
Hemant Choudhary, Shun Nishimura, and Kohki Ebitani*
Bimetallic CoPd nanoparticles (NPs) on boehmite (AlOOH) were
synthesized under hydrothermal conditions using three differ-
ent capping agents for the facile utilization of formic acid (FA)
as a hydrogen source. The CoPd NPs capped with N,N-dime-
thyldodecylamine N-oxide (DDAO) supported on AlOOH
dispersive spectroscopy, XRD, and X-ray absorption spectrosco-
py (XAS) studies. X-ray photoelectron spectroscopy and XAS
supported the partial electron transfer phenomenon in CoPd-
DDAO NPs. The as-prepared CoPd-DDAO/AlOOH catalyst
showed activity for the utilization of FA formed in situ from
biomass for the hydrogenation of MAn. It suggested that the
DDAO capping agent contributed strongly to the favorable
electronic/geometric changes in CoPd alloy for the facile uti-
lization of FA.
(
CoPd-DDAO/AlOOH) exhibited superior catalysis and recycla-
bility in the hydrogenation of maleic anhydride (MAn) in water
without metal leaching. The formation of monodispersed
CoPd-DDAO NPs on AlOOH that contained both cobalt oxides
and CoPd alloy in each NP was indicated by TEM with energy-
Introduction
Recent research to overcome economic hurdles in fuel cell
technology has introduced various systems for the catalytic de-
(and in turn increases cost) to achieve a high catalytic activity.
Of late, it has been found that the incorporation of an earlier
transition metal can enhance the two-electron oxidation pro-
[1–6]
hydrogenation of formic acid (FA) into hydrogen.
FA is a sus-
[
7–11]
[6]
tainable and convenient hydrogen storage material
that
In spite of
cess dramatically because of their oxophilic properties. Simi-
[12–15]
can be obtained from biomass in high yields.
lar effects of alloying Pd with transition metals have been ob-
[
23–25]
the spectacular research accomplishments in the dehydrogena-
tion of FA, limited efforts have been made to replace hazard-
served for the oxygen reduction reaction.
A significant accomplishment has been made in the synthe-
[
26–35]
ous H by FA in catalytic hydrogenation reactions. However,
sis of colloidal NPs using various methods,
and some stud-
2
the scope for the synthesis of efficacious heterogeneous cata-
lysts is wide, and supported metal nanoparticles (NPs) are of
prime interest. The resulting interactions of dispersed NPs on
a support and their impact on the composition, structure, and
catalytic performances of NPs have been well understood in
ies exist for the simple synthesis of stable supported MPd (M=
[
17,18,36–38]
Fe, Ni, Co, Au, Ru) alloy NPs for catalytic research.
Ho-
mogeneous polymer-protected metal NPs have the advantages
of a high degree of dispersion with serious issues of separation
and sustainability for wider applications. Thus, it becomes nec-
essary to develop stable and highly active heterogeneous NP
(or supported NP) catalysts.
[
16–20]
the past decades.
It has been reported that not only the
metal–support interactions but also the type of capping agent
[16–20]
influences the electronic properties of NPs.
Pd-based cata-
Hydrothermal methods have gained popularity in the syn-
thesis of advanced materials, which include nanomaterials,
mainly because of the reasonable product quality (narrow size
distribution and good crystallinity) and high reproducibili-
lysts are more efficient for FA decomposition than the over-
priced Pt catalysts used commonly because of the facilitated
two-electron oxidation step of FA that promotes the dehydro-
genation pathway (toward H and CO ) rather than the dehy-
[
39–41]
ty.
Recently, we synthesized a CuOx NPs supported on
2
2
[21,22]
dration pathway (toward H O and CO).
Unfortunately, the
MgO catalyst using cetyltrimethylammonium bromide (CTAB)
as a capping agent (denoted as Cu-CTAB/MgO) by a simple hy-
drothermal methodology to obtain a stable and active catalyst
for the synthesis of FA and lactic acid from biomass resour-
2
limiting step is the adsorption/dissociation of FA on the Pd cat-
alyst surface, which demands increased quantities of catalyst
[
15]
[
a] H. Choudhary, Dr. S. Nishimura, Prof. Dr. K. Ebitani
School of Materials Science
ces. These results motivated us to extend the preparation
method for a bimetallic catalyst such as CoPd and to examine
its catalytic activity for the industrially important maleic anhy-
dride (MAn) hydrogenation reaction toward succinic acid (SA),
Japan Advanced Institute of Science and Technology
1
-1 Asahidai, Nomi, Ishkawa 923 1292 (Japan)
E-mail: ebitani@jaist.ac.jp
[
42]
a C-4 building block chemical. Very recently, our group syn-
thesized supported metal catalysts for efficient utilization of FA
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500161.
ChemCatChem 2015, 7, 2361 – 2369
2361
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
in the hydrogenation reactions of 5-hydroxymethylfuraldehyde,
formed with the corresponding monometallic Pd or Co cata-
lysts prepared by same procedure (entries 2–3). Pd-DDAO/
AlOOH possessed some catalytic activity (29% yield) for the hy-
drogenation reaction, whereas Co-DDAO/AlOOH failed to show
any activity even after 5 h of reaction time.
[43–45]
levulinic acid, and nitroarenes.
Continuous research efforts
in the effective and facile utilization of FA under moderate
conditions with decreased metal content for industrially impor-
tant catalytic reactions paved the path for this research.
As pioneers in this field, Toshima et al. have reported the
role of poly(N-vinyl-2-pyrrolidone) (PVP) on the geometric,
To elucidate the effect of the DDAO capping agent, CoPd
catalysts with and without other common capping agents
were also prepared by the same procedure. From our previous
[
46–49]
physical, and chemical properties of NPs.
Our group has
[18]
[50]
[19–20]
[15]
[15]
also demonstrated PVP, acrylate, starch,
and CTAB
studies on the use of capping agents, we selected CTAB and
[
18]
as efficient capping agents that influence the formation mech-
anism of NPs and/or the properties of the constructed active
centers on supported NP catalysts.
PVP to compare with DDAO. However, the CoPd catalysts
capped with CTAB or PVP hardly facilitated the hydrogenation
reaction with FA ( ꢀ35% yields; Table 1, entries 5–6). Fumaric
acid was observed as the only byproduct in some of the cata-
lytic hydrogenations of MAn under our reaction conditions.
The real Co loadings were in the range of 0.55–1.02 wt%,
which were much lower than the theoretical value (2.5 wt%) in
all of the Co catalysts (entries 1 and 3–6). The molar composi-
tions of the capped CoPd catalyst from inductively coupled
plasma atomic emission spectroscopy (ICP-AES) were found to
be Co0.23Pd0.77-DDAO/AlOOH (i.e., 0.75 wt% Co and 2.53 wt%
Pd loading), Co0.20Pd0.80-CTAB/AlOOH, and Co0.18Pd0.82-PVP/
AlOOH. The loading amount of Co cannot explain the differen-
ces between the catalysts.
For the hydrothermal synthesis of the CoPd catalyst in this
study, we chose N,N-dimethyldodecylamine N-oxide (DDAO;
Figure 1), a nonionic surfactant, as the capping agent. As
Figure 1. Chemical structure of DDAO.
DDAO possesses strong hydrophilicity and a similar functionali-
ty to PVP, it is expected to affect both the physical and chemi-
cal properties of the produced NPs.
The noncapped CoPd catalyst, Co0.28Pd0.72/AlOOH estimated
by ICP-AES, had considerable activity (56% yield) in the first
run with a high Co loading (entry 4). However, significant Co
leaching was observed after the first catalytic cycle; the initial
loaded amount of Co (0.94 wt%) decreased drastically to
0.39 wt% (entry 4e). Thus, Co species were hardly preserved
on catalyst surface during the reaction without a capping
agent. In other words, this result established the efficiency of
DDAO to retain metal species on AlOOH during the catalytic
runs.
Herein, we demonstrate the preparation (under hydrother-
mal conditions) and superior catalysis of a robust supported,
capped, bimetallic CoPd catalyst for the hydrogenation of MAn
to SA using FA as an inexpensive and sustainable hydrogen
source. The characterization of the DDAO-stabilized bimetallic
CoPd NPs by TEM, XRD, X-ray photoelectron spectroscopy
(
XPS), and X-ray absorption spectroscopy (XAS) and the one-
pot synthesis of SA using FA formed from glucose are also de-
scribed.
[a]
Table 1. Hydrogenation of MAn using FA.
Results and Discussion
Hydrogenation of MAn to SA
using FA
The hydrogenation of MAn, an
industrially important pathway
Entry
Catalyst
Time
[h]
Co
[wt%]
Pd
[wt%]
Conversion
[%]
Yield
[%]
[
42]
[b]
[b]
[c]
[c]
to produce SA, was chosen as
the test reaction to evaluate the
catalytic activity of supported
mono- and bimetallic catalysts.
The hydrogenation was per-
formed using FA as a hydrogen
source. DDAO-capped bimetallic
CoPd NPs supported on AlOOH
[
d]
e]
[d]
[e]
[d]
[d]
1
2
3
4
5
6
7
8
9
1
CoPd-DDAO/AlOOH
Pd-DDAO/AlOOH
Co-DDAO/AlOOH
CoPd/AlOOH
CoPd-CTAB/AlOOH
CoPd-PVP/AlOOH
3
5
5
3
3
3
3
3
3
3
3
3
0.75, 0.71
0
2.53, 2.52
2.64
0
2.44, 2.41
2.49
>99, >99
>99, >99
29
0
56
36
35
74
>99
0
40
0
72
52
4
98
>99
0
1.02
0.94, 0.39
0.63
0.55
0
0.75
0
0
[
2.51
[f]
Pd/Al
2
O
3
(commercial)
5
[
g]
CoPd-DDAO/AlOOH
AlOOH
blank
CoPd-DDAO/AlOOH
CoPd-DDAO/AlOOH
2.53
0
0
2.53
2.53
(
CoPd-DDAO/AlOOH) exhibited
0
0
0
>99
0
0
98
[
h]
excellent catalytic activity for the
selective hydrogenation of MAn
to SA (>99% yield; Table 1,
11
12
0.75
0.75
[
i]
[
a] Reaction conditions: MAn (0.5 mmol), FA (1.9 mmol), catalyst (25 mg), 353 K, H
clave. [b] Determined by ICP-AES. [c] Calculated by HPLC using a calibration curve method. [d] Fifth catalytic
run. [e] After the first catalytic run. [f] Quoted from the manufacturer’s product specifications. [g] H (0.1 MPa).
2
O (5 mL), Teflon-lined auto-
[
51]
entry 1). The superiority of the
bimetallic CoPd catalyst was es-
tablished by experiments per-
2
[
h] Without FA. [i] 2,6-Di-tert-butyl-p-cresol (0.15 mmol) was used as a radical scavenger.
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2362
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
The 5 wt% Pd/Al O commercial catalyst afforded a high
ucts after the treatment of only FA (without MAn) with CoPd-
DDAO/AlOOH were collected and analyzed by GC with thermal
conductivity detection (TCD) and an active carbon column. Al-
2
3
conversion (98%) because of the high Pd amount with moder-
ate SA yields (74%; entry 7). CoPd-DDAO/AlOOH also hydro-
genated MAn efficiently in the presence of H (entry 8). The re-
though a peak that corresponds to CO was detected, no sig-
2
2
action could not progress in the absence of Pd at all (entries 3,
nals for H appeared in the chromatogram (Figure S3). The dis-
2
[
22]
9
, and 10), which indicates that the Pd species acted as the
sociation of FA to CO by a dehydrogenation pathway and
2
active center for the catalysis. Without FA (hydrogen source),
the reaction did not proceed (entry 11). The catalytic activity
was investigated carefully as a function of temperature, time,
and the amount of FA in the reaction medium (Tables S1 and
S2 and Figure S1). Then, 3 h and 353 K with 1.9 mmol of FA
were found to be the best reaction conditions for MAn hydro-
genation over CoPd-DDAO/AlOOH. Notably, CoPd-DDAO/
AlOOH retained a high catalytic activity even after the fifth run
of hydrogenation (Table 1, entry 1d and Figure S2). It was as-
certained that CoPd-DDAO/AlOOH had a similar composition
to Co0.22Pd0.78-DDAO/AlOOH (i.e., 0.71 wt% Co and 2.52 wt%
the presence of adsorbed hydrogen as an ionic species in our
reaction medium are proposed from these observations.
TEM of CoPd-capped/AlOOH
TEM was measured to characterize the bimetallic CoPd NPs.
Typical TEM images and particle size distributions of capped
and noncapped bimetallic CoPd NPs on AlOOH and the com-
mercial Pd/Al O catalyst are shown in Figure 2. Well-dispersed
2
3
and well-shaped NPs were obtained for all catalysts. Interest-
ingly, the DDAO-capped bimetallic CoPd NPs exhibited a wider
particle size distribution with an average diameter of 6.4 nm
(Figure 2a and g) than the other bimetallic CoPd NPs. CTAB-
capped CoPd NPs afforded the biggest size of 7.5 nm (Fig-
ure 2b and h), whereas noncapped CoPd NPs had an average
diameter of 5.5 nm (Figure 2d and j). PVP-capped CoPd NPs
exhibited an intermediate average particle size of 6.2 nm (Fig-
ure 2c and i). These results suggest that the formation process
and/or the growth rate of bimetallic CoPd NPs varies in the
presence of capping agents under the hydrothermal condi-
tions. TEM images for commercial 5 wt% Pd/Al O showed
[52]
Pd loading) even after five runs (entry 1d).
To understand the nature of FA dissociation and clarify the
reaction pathway over CoPd-DDAO/AlOOH, a radical scavenger
was added to the reaction mixture. The result in Table 1,
entry 12 showed that there was no influence of the radical
scavenger (2,6-di-tert-butyl-p-cresol, 0.15 mmol) on the hydro-
genation of MAn using FA over the CoPd-DDAO/AlOOH cata-
lyst. These results ruled out the possibility of any radical inter-
mediate (hydrogen radical or carbon-centered free radical)
within the reaction medium. Additionally, the gaseous prod-
2
3
Figure 2. a–f) TEM images and g–l) particle size distributions of a, g) CoPd-DDAO/AlOOH, b, h) CoPd-CTAB/AlOOH, c, i) CoPd-PVP/AlOOH, d, j) CoPd/AlOOH, e,
k) Pd/Al , and f, l) CoPd-DDAO/AlOOH after the fifth catalytic run. Inset shows the TEM images at higher magnifications (scale bar is 20 nm).
2
O
3
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2363
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
a narrow particle size distribution and a mean particle diame-
ter of 3.4 nm (Figure 2e and k). The TEM images and size distri-
bution of CoPd-DDAO/AlOOH after the fifth catalytic run were
similar to those of the fresh catalyst (cf. Figure 2a and g and
2
f and l), which demonstrates the stability of the catalyst
capped with DDAO. TEM images of the DDAO-capped mono-
metallic catalyst and the bare support (AlOOH) were also re-
corded (Figure S4).
The high-angle annular dark-field scanning transmission
electron microscopy (HAADF-STEM) images shown in Figure S5
reveal the crystalline nature of CoPd-DDAO/AlOOH. The com-
positional mapping was performed by STEM with energy-dis-
persive spectroscopy (EDS) mapping and HAADF-STEM. Inspec-
tion of the elemental mapping image shows the uniform distri-
bution of Co and Pd elements within the bimetallic CoPd NPs
with a higher concentration of Pd than Co. The HAADF-STEM
line analysis shown in Figure S5 suggests the composition is
Co Pd . Similar results in elemental mapping images were
Figure 3. A) XRD patterns in the range of 2q=8–808 and B) with empha-
sized detail in the range of 2q=36–448 of a) AlOOH, b) Co-DDAO/AlOOH,
c) Pd-DDAO/AlOOH, d) CoPd-DDAO/AlOOH, e) CoPd-CTAB/AlOOH, f) CoPd-
PVP/AlOOH, and g) CoPd/AlOOH.
could be explained in terms of d–d bonding and the s–d
charge transfer effects as reported for other bimetallic systems
0.1
0.9
observed at various places, which demonstrate the homogene-
ity of the bimetallic CoPd NPs (consistent compositional distri-
bution within each NP) throughout the catalyst structure. The
existence of bimetallic CoPd NPs over the AlOOH surface as an
alloy is substantiated by STEM. At some places darker and
brighter regions were observed on the NPs, however, the line
analysis disproved the formation of a core–shell structure.
However, the composition of the NPs estimated by STEM-EDS
line analysis (Co Pd ) differed from that from ICP-AES
[
54,55]
such as Ni/Pt, Pd/Au, and Pd/Ag.
An intense line that corresponds to CoPd in the XRD pattern
of CoPd-CTAB/AlOOH (Figure 3e) implies the presence of large
crystals of the bimetallic CoPd particles (crystalline size in the
(111) plane is estimated to be 49.4 nm), although these were
hardly observed in TEM analysis. CoPd-DDAO/AlOOH has
a stable structure under the reaction conditions; similar elec-
tron micrographs (Figure 2 f and l) and XRD patterns (Fig-
ure S7) are obtained even after the fifth catalytic run of the
MAn hydrogenation.
0.1
0.9
(
Co0.23Pd0.77). This implied that the Co0.23Pd0.77-DDAO/AlOOH
catalyst was composed of not only the CoPd alloy NPs with
a high concentration of Pd but also isolated Co species, al-
though the latter exhibited little activity for the reaction
XPS of supported CoPd catalysts
(
Table 1, entry 3). Neither large isolated CoO particles nor par-
x
ticles with a high Co composition were observed by micro-
scopic analysis. To account for such differences, more detailed
investigations of the CoPd-DDAO/AlOOH were performed by
other spectroscopic methods.
XPS measurements were employed to investigate the oxida-
tion states of Co and Pd species and the effect of alloying on
each. The Pd3d states of the various catalysts are shown in
Figure 4, in which the Pd3d5/2 spectral lines are observed at
a binding energy (BE) around 334 eV. A significant negative
shift in the BE values for all catalysts was noticed in compari-
XRD patterns of CoPd-capped/AlOOH
[
56–60]
son to pure Pd (BE=335.1 eV).
The BEs of the Pd3d state
To gain more insight into the bimetallic CoPd alloy, the XRD
patterns were obtained for the CoPd-capped/AlOOH catalysts
and various AlOOH-supported monometallic and bimetallic
catalysts (Figure 3A). Diffraction peaks of the AlOOH structure
appeared at 2q=14.04, 28.36, 38.42, 49.06, 55.14, 64.94, and
in these catalysts are attributed to the electron-rich metallic
state of Pd as they were much lower than that of palladium
[
56–60]
oxide (BE=337.0 eV).
In the cases of bimetallic CoPd cata-
lysts, negative shifts in BE supposedly indicate an electron
transfer phenomenon from Co to Pd in CoPd NP, which is in
agreement with the Pauling electronegativities of Pd (2.2) and
Co (1.88).
7
1.848 for all catalysts. No diffraction signals that correspond
to CoO or Co O were found in any samples (Figure S6). This
3
4
indicates that either these species were absent or that the
crystalline sizes of the isolated Co species were too small to be
detected by XRD. At a 2q value of around 408, the bimetallic
CoPd NPs catalyst showed a diffraction peak at higher 2q
values in comparison to Pd-DDAO/AlOOH (Figure 3c–g). The
area of 2q=36–448 is shown in Figure 3B to highlight the dif-
ferences in monometallic and bimetallic catalysts. A similar
shift for the (111) lattice spacing of the CoPd (also observed as
a striped pattern for the closed packing plane of the face-cen-
Additionally, from comparison of the capped and noncap-
ped bimetallic CoPd catalysts, the low BE (334.0 eV) of the
noncapped bimetallic CoPd catalyst (CoPd/AlOOH) could be
distinguished from other capped bimetallic CoPd catalysts, for
which the energy of the Pd3d5/2 position increased in order
from CoPd-DDAO/AlOOH (334.2 eV) to CoPd-PVP/AlOOH
(334.4 eV) and CoPd-CTAB/AlOOH (334.5 eV). The higher BEs of
the capped CoPd catalysts than noncapped CoPd/AlOOH
could be accounted for by the synergistic effect because of
the coordination of the capping agent. If the capping agent
coordinates to metal NPs, electron donation from the capping
[
37,53]
tered cubic (fcc) structure in TEM) has been reported.
The
shift in the diffraction peak for the bimetallic nanostructure
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2364
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
mained on AlOOH, 3) the most stable Co species in the CoPd
alloy was produced (rather than noncapped CoPd), which led
to the highest activity for the hydrogenation of MAn using FA.
XAS of CoPd catalysts
XAS has been recognized as a powerful technique for the de-
tailed inspection of the electronic states and structures of
[
50,64–67]
nanomaterials.
XAS experiments were, therefore, con-
ducted for bimetallic CoPd catalysts to further clarify the nano-
structure and electronic interactions induced by the capping
agent. X-ray absorption near-edge structure (XANES) analysis
of the catalysts at the Pd K-edge and Co K-edge are shown in
Figure S9. Pd K-edge and Co K-edge spectra of reference mate-
rials (metal foils, oxides, and salts) are shown in Figure S10.
The Pd K-edge XANES features (Figure S9A) were similar to
that of Pd foil, which indicates the presence of zero-valent Pd
as the dominant state in the catalysts. In accordance with
Co2p XPS, the Co K-edge XANES analysis (Figure S9B) had
a close resemblance to that of cobalt oxides and was signifi-
cantly different from that of Co foil.
Figure 4. XPS spectra of the Pd3d states of a) Pd-DDAO/AlOOH, b) CoPd/
AlOOH, c) CoPd-DDAO/AlOOH, d) CoPd-PVP/AlOOH, and e) CoPd-CTAB/
AlOOH.
L-edge XANES analysis, which is an electric-dipole allowed
transition (p!d), affords more intense and high-resolution ob-
agent to the coordinated metal is expected. As it may enhance
the negative flow onto Pd atoms in bimetallic CoPd NPs, back
donation from d states in Pd towards neighboring Co and/or
the capping agent (CTAB, PVP, DDAO) occurs. These synergistic
phenomena supposedly determine the back shifts in capped
CoPd catalysts to higher energy BE values compared with the
noncapped CoPd catalyst. Among the three capped CoPd cata-
lysts, DDAO favored electron-rich Pd in CoPd NPs. However,
the Pd3d5/2 peak for monometallic Pd-DDAO/AlOOH (29%
yield) appeared at BE=334.3 eV (Figure 4), a little higher than
that of bimetallic CoPd-DDAO/AlOOH (BE=334.2 eV), which
possesses higher catalytic activity (>99% yield). Thus, further
effects of the coexistence of Co in bimetallic CoPd catalysts
need to be discussed (vide infra).
[
64,68,69]
servations.
The most prominent feature in the Pd L -
3
edge XANES is the white line (WL) at around 3175 eV, observed
because of the excitation of electrons from the degenerate 2p
[
64,68,69]
states to the 4d band.
The intensity of the WL is propor-
tional to the number of holes in the nd valence band of the
transition metal species. It is understood that as the hybridiza-
tion of the d state becomes weaker, the peak at the L thresh-
3
[
68,69]
old is enhanced.
The Pd L -edge XANES analysis of bimet-
3
allic catalysts is shown in Figure 5. For all samples, the XANES
intensity was higher than that of Pd black (Pd metal), and thus
the partial oxidation of NPs by air or by the coordination of
the capping agent and/or the strong hybridization phenomen-
on of Pd states in each sample is expected. CoPd-CTAB/AlOOH
It was expected from the XPS spectra at the Co2p level that
the Co in the catalysts exists as an oxide (CoO and Co O ) in-
3
4
stead of metallic Co. Typically, in the case of CoPd-DDAO/
AlOOH, the Co2p3/2 peak was observed at BE=780.2–780.9 eV
(
(
Figure S8), which is consistent with the BEs of cobalt oxides
[
61–63]
bulk CoO BE=780.6 eV and bulk Co O BE=780.7 eV).
3
4
The absence of a reducing agent such as H during the synthe-
2
sis of CoPd catalysts is considered to be one of the reasons for
the presence of cobalt oxide.
Significant peak broadening for CoPd-CTAB/AlOOH and
CoPd-PVP/AlOOH was observed in both the Pd3d and Co2p
XPS spectra, which could be because of: 1) various oxidation
states of Pd and/or Co species and/or 2) changes in electronic
density on the Pd and/or Co. Thus, it is suggested that CTAB-
and PVP-capped CoPd catalysts possessed various states in Co
and Pd, which is different to the DDAO-capped CoPd catalyst.
On this basis, we summarize tentatively that for CoPd-
DDAO/AlOOH: 1) the active CoPd alloy NPs were formed more
uniformly (i.e., with fewer variations of species) than other
capped CoPd materials, 2) the more electron-rich Pd atoms re-
Figure 5. Pd L
3
-edge of Pd black and various bimetallic CoPd catalysts.
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2365
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
displayed the lowest WL intensity among the bimetallic cata-
lysts. The WL intensity profiles for CoPd-PVP/AlOOH, CoPd-
DDAO/AlOOH, and CoPd/AlOOH were similar and lie above
that of CoPd-CTAB/AlOOH. This suggested that the order of
electron density in Pd4d state is CoPd-CTAB/AlOOH> CoPd/
AlOOH> CoPd-DDAO/AlOOH> CoPd-PVP/AlOOH. This trend
among noncapped and DDAO- or PVP-capped CoPd/AlOOH
supports the XPS results for the Pd3d states.
which had peaks at shorter distances. Additionally, the noncap-
ped bimetallic CoPd catalyst, for which the XRD patterns sug-
gested the presence of CoPd alloy, showed three distinct
peaks at 1.44, 1.98, and 2.72 Š. These results implied that each
bimetallic CoPd catalyst (capped and noncapped) differed in
phase and/or coordination around Co, however, further distinc-
tion in the FTs was problematic because of poor information of
possible variation and the low concentration of Co species in
the catalysts. A detailed study of the structural analysis of the
NPs will be published in the near future.
Thus, the proposed synergistic phenomena between Co, Pd,
and the capping agent described in the XPS section are sup-
ported here. The CTAB-capped CoPd/AlOOH catalyst demon-
strated the highest electron density on Pd4d. As a result of
the large CoPd crystallites observed in the XRD patterns, the
surface CTAB on CoPd-CTAB/AlOOH seems to have little influ-
ence on the CoPd alloy. Therefore, the electron density profile
Mechanistic considerations
[
22]
Based on work by Yoo et al., we propose that CoPd-DDAO/
AlOOH decomposed FA through a dehydrogenation pathway
by the adsorbance of FA on oxophilic Co (vide supra) and the
enhancement of the rate of FA dissociation. A theoretical ap-
proach by Pallassana et al. for the hydrogenation of MAn sug-
gested the adsorption of MAn in a more favorable di-s confor-
of CoPd-CTAB/AlOOH in Pd L -edge XANES (which includes
3
average information in the sample) differed significantly from
that in Pd3d XPS (which shows surface information selective-
ly).
[
70,71]
To understand the detailed structure, we further discuss the
extended X-ray absorption fine structure (EXAFS) analysis of
these catalysts at both the Pd K- and Co K-edge. The EXAFS at
mation on the catalyst surface.
This is supported by IR
spectroscopy performed before and during the reaction to ob-
serve the adsorption and thereby the ring-opening of MAn
into a diacid on the catalyst surface (Figure S14). As a result of
the differences in the electronic charges on the surface of bi-
metallic CoPd-DDAO/AlOOH and the modification of the PdÀ
Pd bond distance because of the insertion of Co into the cata-
lyst structure, a better alignment of the surface Pd atoms for
improved overlap between the metal d orbitals and the p orbi-
3
the Pd K-edge and the Fourier transform (FT) of the k -weight-
ed Pd K-edge EXAFS data could be hardly distinguished for all
catalysts and were similar to that of Pd metal in all cases (Fig-
ure S11). This is because of the high concentration of Pd in the
CoPd alloy NPs that leads to little information of the Pd–Co in-
teraction in Pd XAS measurements. However, Co K-edge EXAFS
analysis would be much informative about the Co–Pd interac-
tions because of the low concentration of Co in the bimetallic
CoPd NPs. The Co K-edge EXAFS analysis of the bimetallic
CoPd catalysts showed significantly different oscillations from
CoO and Co O (Figure S12), although they were very similar to
[
70]
tals of the carbonyl group is expected. Such a geometric
effect decreased the adsorption energy, and hence CoPd-
DDAO/AlOOH shows an enhanced rate for hydrogenation.
These results also suggested that the reaction proceeded over
the catalyst surface as proposed in Figure 6.
3
4
that of CoO in the XANES area (Figures S9 and S10). Such
marked differences in the EXAFS oscillations from that of the
oxide species is strong proof of not only the existence of iso-
As the reaction progresses, FA adsorbs on the surface of
CoPd-DDAO/AlOOH and CO is released. As a result of the dif-
2
ferential charge on CoPd-DDAO/AlOOH (vide supra) the hy-
lated CoO species but also the
x
alloying of Co species with Pd
and/or further variety in the bi-
metallic CoPd catalysts.
3
The FT of k -weighted Co K-
edge EXAFS of the three capped
bimetallic CoPd catalysts dis-
played two broadened peaks
[37]
(
Figure S13). Previously,
CoPd
alloy showed a peak at 2.1 Š
with a shoulder at 1.6 Š in the
FT of Co K-edge EXAFS data. Al-
though the PVP- and DDAO-
capped CoPd catalysts had
peaks around 2.35 Š, it is hard to
discuss their origin from the FTs
3
at this stage. The FTs of the k -
weighted EXAFS data of CoPd-
DDAO/AlOOH and CoPd-PVP/
AlOOH were very different from
Figure 6. Proposed pathway for the hydrogenation of MAn over CoPd-DDAO/AlOOH using FA as a hydrogen
that
of
CoPd-CTAB/AlOOH, source.
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2366
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
dride dwells on electron-deficient Co species, and Pd, which is
electron rich, adsorbs the proton (Figure 6). Simultaneously,
and it could be reused effectively. Electron microscopy obser-
vations show that CoPd-DDAO/AlOOH had a mean particle size
of 6.4 nm with uniform distribution of Co and Pd within each
bimetallic CoPd nanoparticle. XRD, X-ray photoelectron spec-
troscopy, and X-ray absorption spectroscopy suggested the
presence of Co–Pd interactions in the bimetallic CoPd catalyst.
Furthermore the alloying of Co with Pd in the presence of
DDAO afforded electron-rich Pd and modified the PdÀPd bond
distance. The electron-rich Pd enhanced the adsorption/disso-
ciation of substrates, and the change in interatomic distances
facilitated a better alignment of the metal d orbital with the
carbonyl p orbitals on the catalyst surface, which enhanced
the rate of maleic anhydride hydrogenation into succinic acid.
Additionally, CoPd-DDAO/AlOOH in combination with Cu-
CTAB/MgO provides a possibility for the direct utilization of
abundant biomass-based glucose as a hydrogen source for var-
ious hydrogenation reactions. This paper introduces a hydro-
thermal strategy to create robust supported bimetallic nano-
particles in the presence of a capping agent.
[
70]
MAn attaches to the CoPd surface with a di-s conformation.
The ring opens in water into a diacid form (Figure S14), and
the proton from the Pd atom is transferred to the C=C bond.
Similarly, another hydrogen atom is transferred to the other
carbon atom to produce SA and regenerate the active catalyst.
The rate of MAn hydrogenation was found to vary as a function
of concentration of both MAn and FA, which indicates compet-
[6]
itive adsorption. In accordance with a previous study, we pro-
pose the adsorption/dissociation of MAn and/or FA on the cat-
alyst surface as the rate-determining step in this catalysis.
These results are in agreement with the activity profiles of
CoPd catalysts and also explain the high catalytic activity of
CoPd-DDAO/AlOOH. The presence of electron-rich Pd (and ox-
ophilic Co) in CoPd-DDAO/AlOOH accelerated the adsorption
and thereby the dissociation of FA under the reaction condi-
tions, and thus an efficient catalysis was observed.
Direct utilization of glucose as a hydrogen source using
CoPd-DDAO/AlOOH
Experimental Section
Chemicals
Our previous efforts succeeded in the effective production of
[15]
FA from glucose using the Cu-CTAB/MgO catalyst. The fruit-
ful outcome of hydrogenation using CoPd-DDAO/AlOOH moti-
vated us to combine the two reactions into a one-pot, two-
step strategy (Scheme 1). This strategy focused on the synthe-
Cobalt acetate (Co(OAc) ·4H O), palladium acetate (Pd(OAc)2),
2
2
[72]
AlOOH, 5 wt% Pd/Al O , d-(+)-glucose, CTAB, FA, Cu(NO ) ·6H O,
2
3
3 2
2
30% H O , and standard solutions (1000 ppm) of palladium and
2 2
cobalt were purchased from Wako Pure Chemical Industries, Ltd.
Acetic acid, SA, MgO, and H SO were procured from Kanto Chemi-
2
4
cal Co., Inc. Tokyo Chemical Industry Co., Ltd. supplied MAn and
fumaric acid, whereas DDAO was obtained from Sigma–Aldrich,
Co. LLC. Acros Organics provided PVP (K12, average molecular
weight 3500).
Catalyst preparation
Surfactant/polymer-capped mono- or bimetallic NPs supported on
AlOOH were synthesized by a hydrothermal method as demon-
[15]
strated previously with some modifications.
Typically, Co(OA-
Scheme 1. Hydrogenation of MAn using glucose as a hydrogen source
through FA formation.
c) ·4H O (0.42 mmol) and/or Pd(OAc) (0.24 mmol) were dispersed
2
2
2
in acetic acid (150 mL) and capping agent (0.5 mmol), followed by
the addition of water (3 mL) into the paste. AlOOH (1.0 g) was dis-
persed in deionized water (25 mL), to which the metal/capping
agent solution was added dropwise under stirring. The mixture
was stirred vigorously 3 h at RT. The obtained mixture was sealed
in a 100 mL Teflon-lined autoclave, heated to 453 K at a heating
sis and utilization of FA in the same reaction flask. We elucidat-
ed that the filtration of Cu-CTAB/MgO after step 1 and main-
taining the temperature at 393 K for hydrogenation could
allow the use of glucose as a hydrogen source to yield 8% SA
after 3 h (Table S3).
À1
rate of 6 Kmin in an oven, and maintained at the same tempera-
ture for 24 h. The oven was allowed to cool slowly to RT. The ob-
tained solid was washed with deionized water until the pH of the
filtrate was neutral, followed by washing with ethanol before
drying in vacuo overnight at RT.
Conclusions
The preparation of CoPd nanoparticles capped with N,N-dime-
thyldodecylamine N-oxide (DDAO) supported on AlOOH
(
CoPd-DDAO/AlOOH) was performed under hydrothermal con-
Catalytic testing
ditions without a reducing agent. The DDAO-capped bimetallic
CoPd catalyst exhibited higher activity than the corresponding
monometallic or bimetallic CoPd catalysts with other capping
agents (such as poly(N-vinyl-2-pyrrolidone) or cetyltrimethy-
lammonium bromide; CTAB) for the hydrogenation of maleic
anhydride using formic acid as a sustainable hydrogen source
All experiments to test the catalytic activity were performed in
a 50 mL Teflon-lined autoclave unless otherwise stated. The catalyt-
ic activity was evaluated for MAn hydrogenation into SA in an
aqueous medium. Typically, MAn (0.5 mmol) was dissolved in de-
ionized water (5 mL). Catalyst (25 mg) was added to the solution,
followed by the addition of FA (1.9 mmol). The autoclave was
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2367
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
sealed and mounted in a preheated oil bath at 353 K. The mixture
was allowed to react for various time intervals with continuous
magnetic stirring. After the reaction, a part of the resultant solution
was diluted 20 times with deionized water, and the catalyst was re-
moved by filtration through a Milex-LG 0.20 mm filter. The obtained
filtrate was analyzed by HPLC (WATERS 600) by using an Aminex
HPX-87H column (Bio-Rad Laboratories, Inc.) attached to a refractive
index detector. Aqueous 10 mm H SO (as a mobile phase) was run
their support in HADDF-STEM-EDS and XAS (KEK-PF) studies, re-
spectively. H.C. extends his thanks to the Japan Society for the
Promotion of Science (JSPS) for a fellowship and KAKENHI (No.
26-12396; Grant-in-Aid for JSPS Fellows). This work is partially
supported by KAKENHI (No. 25820392; Grant-in-Aid for Young
Scientists (B)) and the Mitani Foundation for Research and Devel-
opment.
2
4
through the column (maintained at 323 K) at a flow rate of
À1
0
.5 mLmin . The conversion and yield(s) were determined with
Keywords: formic acid · hydrogenation · capping agent ·
palladium · supported catalysts
a calibration curve method.
Recycling tests were performed to check the stability of the syn-
thesized CoPd-DDAO/AlOOH catalyst during the reaction. The cata-
lyst was separated from the reaction mixture by centrifugation.
The supernatant liquid was stored, and the analysis of products
and the leaching test of catalysts were performed. The residual cat-
alyst was washed by centrifugation with deionized water. Finally,
the catalyst was dried in vacuo overnight. Fresh substrates and re-
agents were added to the catalyst, and the reaction was performed
again.
[1] V. Mazumder, S. Sun, J. Am. Chem. Soc. 2009, 131, 4588–4589.
[2] V. Mazumder, Y. Lee, S. Sun, Adv. Funct. Mater. 2010, 20, 1224–1231.
[3] A. Majewski, D. J. Morris, K. Kendall, M. Wills, ChemSusChem 2010, 3,
431–434.
[
[
4] A. Boddien, D. Mellmann, F. Gartner, R. Jackstell, H. Junge, P. J. Dyson, G.
Laurenczy, R. Ludwig, M. Beller, Science 2011, 333, 1733–1736.
5] K. Tedsree, T. Li, S. Jones, C. W. A. Chan, K. M. K. Yu, P. A. J. Bagot, E. A.
Marquis, G. D. W. Smith, S. C. E. Tsang, Nat. Nanotechnol. 2011, 6, 302–
307.
[6] V. Mazumder, M. Chi, M. N. Mankin, Y. Liu, O. Metin, D. Sun, K. L. More,
S. Sun, Nano Lett. 2012, 12, 1102–1106.
[
[
7] F. Joó, ChemSusChem 2008, 1, 805–808.
8] T. C. Johnson, D. J. Morris, M. Wills, Chem. Soc. Rev. 2010, 39, 81–88.
Characterization
The crystal structure was analyzed by powder X-ray diffraction
[9] M. Grasemann, G. Laurenczy, Energy Environ. Sci. 2012, 5, 8171–8181.
10] W. Gan, P. J. Dyson, G. Laurenczy, ChemCatChem 2013, 5, 3124–3130.
11] S. Enthaler, A. Bruck, A. Kammer, H. Junge, E. Irran, S. Gulak, ChemCat-
Chem 2015, 7, 65–69.
[
[
(
PXRD) by using a SmartLab diffractometer (Rigaku Co.) using CuKa
radiation (l=0.154 nm) at 40 kV and 30 mA in the range of 2q=
–808. The diffraction patterns were analyzed using the database
8
[
[
[
12] J. J. Bozell, Science 2010, 329, 522–523.
of the Joint Committee of Powder Diffraction Standards (JCPDS).
For ICP-AES, an ICPS-7000 ver. 2 (Shimadzu Co.) was employed to
quantify the real amounts of Co and Pd on AlOOH and to evaluate
metal leaching, if any, during the reaction. Contents of metal (Co
and/or Pd) in the catalyst and/or the reaction medium were esti-
mated by a calibration curve method using the standard solutions.
An H-7650 TEM (Hitachi, Ltd.) operating at 100 kV was utilized to
acquire the morphology of catalyst. HAADF-STEM images and ele-
mental mapping analyses were recorded by using a JEM-ARM200F
13] R. Xing, W. Qi, G. W. Huber, Energy Environ. Sci. 2011, 4, 2193–2205.
14] Z. Tang, W. Deng, Y. Wang, E. Zhu, X. Wan, Q. Zhang, Y. Wang, Chem-
SusChem 2014, 7, 1557–1567.
[15] H. Choudhary, S. Nishmura, K. Ebitani, Appl. Catal. B 2015, 162, 1–10.
[16] J. H. A. Martens, R. Prins, D. C. Konningsberger, J. Phys. Chem. 1989, 93,
3179–3185.
[
[
17] R. W. Wunder, J. Phillips, J. Phys. Chem. 1996, 100, 14430–14436.
18] S. Nishimura, Y. Yakita, M. Katayama, K. Higashimine, K. Ebitani, Catal.
Sci. Technol. 2013, 3, 351–359.
19] D. Tongsakul, S. Nishimura, K. Ebitani, ACS Catal. 2013, 3, 2199–2207.
20] D. Tongsakul, S. Nishimura, K. Ebitani, J. Phys. Chem. C 2014, 118,
[
[
(
JEOL USA, Inc.) that operated at 200 kV. The samples for TEM
measurements were dispersed in water, and the supernatant liquid
was dropped onto a copper/carbon grid before drying in vacuo
overnight. The electronic state of Co/Pd on AlOOH was analyzed
by XPS. The experiments were conducted by using an AXIS-ULTRA
DLD spectrometer system (Shimadzu Co. and Kratos Analytical
Ltd.) using an Al target at 15 kV and 10 mA in an energy range of
1
1723–11730.
[
21] J. Wang, G. Yin, Y. Chen, R. Li, X. Sun, Int. J. Hydrogen Energy 2009, 34,
8270–8275.
[22] J. S. Yoo, F. Ablid-Pedersen, J. K. Nørskov, F. Studt, ACS Catal. 2014, 4,
1226–1233.
[
[
[
23] J. L. Fernµndez, D. A. Walsh, A. J. Bard, J. Am. Chem. Soc. 2005, 127,
57–365.
24] V. Raghuveer, A. Manthiram, A. J. Bard, J. Phys. Chem. B 2005, 109,
2909–22912.
25] M. H. Shao, K. Sasaki, R. R. Adzic, J. Am. Chem. Soc. 2006, 128, 3526–
527.
3
0
–1200 eV. The BEs were calibrated with the C1s level (284.5 eV) as
an internal standard reference. XAS was performed by using BL-9C
Co K-edge) and BL-9 A (Pd L -edge) at KEK-PF under the approval
2
(
3
of the Photon Factory Program Advisory Committee (Proposal No.
013G586) and BL01B1 (Pd K-edge) at SPring-8 under the approval
3
2
[
[
26] N. Toshima, T. Yonezawa, New J. Chem. 1998, 22, 1179–1201.
27] B. L. Cushing, V. L. Kolesnichenko, C. J. O’Connor, Chem. Rev. 2004, 104,
3893–3946.
of the Japan Synchrotron Radiation Research Institute (JASRI; Pro-
3
posal Nos. 2013B1478 and 2014B1472). FTs of k -weighted EXAFS
À1
data were performed in the range of 3–12 Š for Co K and 3–
[28] R. Ferrando, J. Jellinek, R. L. Johnston, Chem. Rev. 2008, 108, 845–910.
À1
[
[
29] T. K. Sau, A. L. Rogach, Adv. Mater. 2010, 22, 1781–1804.
30] M. Sankar, N. Dimitratos, P. J. Miedziak, P. P. Wells, C. J. Kiely, G. J. Hutch-
ings, Chem. Soc. Rev. 2012, 41, 8099–8139.
31] B. H. Kim, M. J. Hackett, J. Park, T. Hyeon, Chem. Mater. 2014, 26, 59–71.
32] A. K. Singh, Q. Xu, ChemCatChem 2013, 5, 652–676.
1
3 Š for Pd K-edge XAS. All samples were ground and pressed to
pellets with a diameter of 10 mm. The obtained XAS spectra were
analyzed by using Rigaku REX2000 software (ver. 2.5.92). The IR
measurements of samples were performed by using a PerkinElmer
Spectrum 100 FTIR spectrometer.
[
[
[
33] I. Notar Francesco, F. Fontaine-Vive, S. Antoniotti, ChemCatChem 2014,
6, 2784–2791.
[
[
[
34] D. Wu, M. Cao, M. Shen, R. Cao, ChemCatChem 2014, 6, 1731–1736.
35] M. Cao, J. Lin, H. Yang, R. Cao, Chem. Commun. 2010, 46, 5088–5090.
36] P. Lu, T. Teranishi, K. Asakura, M. Miyake, N. Toshima, J. Phys. Chem. B
Acknowledgements
1
999, 103, 9673–9682.
We greatly appreciate Dr. Koichi Higashimine (JAIST, Center for
Nano Materials and Technology) and Dr. Hitoshi Abe (KEK-PF) for
[
37] S. Takenaka, T. Tsukamoto, H. Matsune, M. Kishida, Catal. Sci. Technol.
2013, 3, 2723–2731.
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2368
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
[
[
[
38] D. Wu, M. Cao, R. Cao, Chem. Commun. 2014, 50, 12970–12972.
39] G. Demazeau, J. Mater. Chem. 1999, 9, 15–18.
40] J. Li, Z. Chen, R. J. Wang, D. M. Proserpio, Coord. Chem. Rev. 1999, 190–
[56] B. Schleich, D. Schmeisser, W. Gopel, Surf. Sci. 1987, 191, 367–384.
[57] J. M. Tura, P. Regull, L. Victori, M. Dolors de Castellar, Surf. Interface Anal.
1988, 11, 447–449.
1
92, 707–735.
41] K. Byrappa, T. Adschiri, Prog. Cryst. Growth Charact. Mater. 2007, 53,
17–166.
42] C. Delhomme, D. Weuster-Botz, F. E. Kühn, Green Chem. 2009, 11, 13–
6, and references cited therein.
43] J. Tuteja, H. Choudhary, S. Nishimura, K. Ebitani, ChemSusChem 2014, 7,
6–100.
[58] I. Z. Shyu, K. Otto, W. L. H. Watkins, G. W. Graham, R. K. Belitz, H. S.
Gandhi, J. Catal. 1988, 114, 23–33.
[59] T. J. Sarapatka, J. Phys. Chem. 1993, 97, 11274–11277.
[60] C. J. Jenks, S. L. Chang, J. W. Anderegg, P. A. Thiel, D. W. Lynch, Phys.
Rev. B 1996, 54, 6301–6306.
[61] T. J. Chuang, C. R. Brundle, D. W. Rice, Surf. Sci. 1976, 59, 413–429.
[62] M. Oku, K. Hirokawa, J. Electron Spectrosc. Relat. Phenom. 1976, 8, 475–
481.
[63] B. J. Tan, K. J. Klabunde, P. M. A. Sherwood, J. Am. Chem. Soc. 1991, 113,
855–861.
[
[
[
1
2
9
[
[
[
44] P. A. Son, S. Nishimura, K. Ebitani, RSC Adv. 2014, 4, 10525–10530.
45] J. Tuteja, S. Nishimura, K. Ebitani, RSC Adv. 2014, 4, 38241–38249.
46] N. Toshima, M. Harada, T. Yonezawa, K. Kushihashi, K. Asakura, J. Phys.
Chem. 1991, 95, 7448–7453.
[64] X-ray Absorption: Techniques of EXAFS, SEXAFS and XANES (Eds.: D. C. Ko-
ningsberger, R. Prins), Wiley, New York, 1988.
[
47] M. Harada, K. Asakura, Y. Ueki, N. Toshima, J. Phys. Chem. 1993, 97,
1
0742–10749.
[65] M. Harada, K. Asakura, N. Toshima, J. Phys. Chem. 1994, 98, 2653–2662.
[66] U. Kolb, S. A. Quaiser, M. Winter, M. T. Reetz, Chem. Mater. 1996, 8,
1889–1894.
[
[
48] Y. Wang, N. Toshima, J. Phys. Chem. B 1997, 101, 5301–5306.
49] H. Zhang, T. Watanbe, M. Okumura, M. Haruta, N. Toshima, Nat. Mater.
2
012, 11, 49–52.
[67] S. Nishimura, A. T. N. Dao, D. Mott, S. Maenosono, K. Ebitani, J. Phys.
Chem. C 2012, 116, 4511–4516.
[68] T. K. Sham, Phys. Rev. B 1985, 31, 1888–1902.
[69] T. K. Sham, Phys. Rev. B 1985, 31, 1903–1908.
[70] V. Pallassana, M. Neurock, G. W. Coulston, J. Phys. Chem. B 1999, 103,
8973–8983.
[
[
50] S. Nishimura, D. Mott, A. Takagaki, S. Maenosono, K. Ebitani, Phys. Chem.
Chem. Phys. 2011, 13, 9335–9343.
51] The turnover number for the hydrogenation of MAn (0.5 mmol) with
the CoPd-DDAO/AlOOH is 84 based on the total amount of Pd in the
catalyst.
[
52] The ICP-AES analysis of the reaction mixture after a catalytic run also
underlined the stability of AlOOH (or nonleaching of Al) under the reac-
tion conditions irrespective of the presence or absence of capping
agents during catalyst preparation.
[71] V. Pallassana, M. Neurock, J. Phys. Chem. B 2000, 104, 9449–9459.
[72] The BET surface area and pore volume of the boehmite employed in
2
À1
À1
this study are 465 m g and 0.79 mLg , respectively.
[
[
[
53] D. Sun, V. Mazumder, Ö. Metin, S. Sun, ACS Nano 2011, 5, 6458–6464.
54] E. G. Allison, G. C. Bond, Catal. Rev. 1972, 7, 233–289.
55] J. M. Dominguez, A. Vazquez, A. J. Renouprez, M. J. Jose Yacaman, J.
Catal. 1982, 75, 101–111.
Received: February 17, 2015
Published online on June 26, 2015
ChemCatChem 2015, 7, 2361 – 2369
www.chemcatchem.org
2369
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim