Pd@Pt Core-Shell Nanoparticles with Branched Dandelion-like Morphology as Highly Efficient Catalysts for Olefin Reduction

Article abstract of DOI:10.1002/chem.201503441

A facile synthesis based on the addition of ascorbic acid to a mixture of Na₂PdCl₄, K₂PtCl₆, and Pluronic P123 results in highly branched core-shell nanoparticles (NPs) with a micro-mesoporous dandelion-like morphology comprising Pd core and Pt shell. The slow reduction kinetics associated with the use of ascorbic acid as a weak reductant and suitable Pd/Pt atomic ratio (1:1) play a principal role in the formation mechanism of such branched Pd@Pt core-shell NPs, which differs from the traditional seed-mediated growth. The catalyst efficiently achieves the reduction of a variety of olefins in good to excellent yields. Importantly, higher catalytic efficiency of dandelion-like Pd@Pt core-shell NPs was observed for the olefin reduction than commercially available Pt black, Pd NPs, and physically admixed Pt black and Pd NPs. This superior catalytic behavior is not only due to larger surface area and synergistic effects but also to the unique micro-mesoporous structure with significant contribution of mesopores with sizes of several tens of nanometers.

Full text of DOI:10.1002/chem.201503441

DOI: 10.1002/chem.201503441
Communication
&
Heterogeneous Catalysis |Hot Paper|
Pd@Pt Core–Shell Nanoparticles with Branched Dandelion-like
Morphology as Highly Efficient Catalysts for Olefin Reduction
Kasibhatta Josena Datta,[a] Kasibhatta Kumara Ramanatha Datta,[a] Manoj B. Gawande,*[a]
[a]
[a]
[b]
[b]
[c]
ˇ
Vaclav Ranc, Klµra CØpe, Victor Malgras, Yusuke Yamauchi, Rajender S. Varma, and
Radek Zboril*[a]
pendent on their size, shape, composition, and microstruc-
ture.[2] Recently, numerous efforts have been made for the as-
Abstract: A facile synthesis based on the addition of as-
corbic acid to a mixture of Na2PdCl4, K2PtCl6, and Pluronic
P123 results in highly branched core–shell nanoparticles
(NPs) with a micro–mesoporous dandelion-like morpholo-
gy comprising Pd core and Pt shell. The slow reduction ki-
netics associated with the use of ascorbic acid as a weak
reductant and suitable Pd/Pt atomic ratio (1:1) play a prin-
cipal role in the formation mechanism of such branched
Pd@Pt core–shell NPs, which differs from the traditional
seed-mediated growth. The catalyst efficiently achieves
the reduction of a variety of olefins in good to excellent
yields. Importantly, higher catalytic efficiency of dande-
lion-like Pd@Pt core–shell NPs was observed for the olefin
reduction than commercially available Pt black, Pd NPs,
and physically admixed Pt black and Pd NPs. This superior
catalytic behavior is not only due to larger surface area
and synergistic effects but also to the unique micro–
mesoporous structure with significant contribution of
mesopores with sizes of several tens of nanometers.
sembly of bimetallic NPs with a core–shell or an alloyed struc-
ture, given their remarkable catalytic properties that are often
superior to those of their monometallic counterparts.[3] Often,
the addition of a second metallic component has a greater po-
tential for enhancing the functionalities and performance of
pure metal components due to significant synergistic effects.[4]
Bimetallic core–shell NPs with well-defined shapes have
been synthesized from noble metals such as Au, Pt, Pd, and Ag
through heteroepitaxial growth of one metal on the surface of
the other metal.[5] For instance, a Pt monolayer supported on
a Pd surface shows an improved activity for the oxygen reduc-
tion reaction (ORR) in comparison to the pure Pt surface.[6] The
interface between the Pd core and the Pt shell of Pd@Pt core–
shell NPs provides a favorable environment for metal hydride
formation, making this material useful for several applications.
There are several strategies to prepare Pd@Pt core–shell NPs,
including seed-mediated growth, co-reduction, and galvanic
replacement.[7]
Recently, particular attention has been focused on the fabri-
cation of bimetallic core–shell NPs with highly branched/
porous structures because of their promising catalytic and
electronic properties. These assemblies exhibit high-index crys-
tal facets on concave pore surfaces, defined as a set of Miller
indices (hkl) with at least one integer higher than unity allow-
ing easier access to active sites. More importantly, the porous
framework allows the interaction or accessibility of reactants
with more active surfaces due to the abundance of pores facili-
tating the overall kinetics of reaction.[8] In continuation of on-
going research on core–shell NPs, especially as nanocatalysts,
herein we describe a facile one-pot synthesis of porous and
highly branched Pd@Pt core–shell NPs at room temperature
without any organic solvents or addition of pre-synthesized
seeds (Scheme 1).
The synthesis of well-defined metal nanoparticles (NPs) with
controlled morphology has been the prime focus of much re-
search, owing to their interesting catalytic, electronic, photon-
ic, and sensing properties.[1] Various NPs with complex poly-
hedral morphologies featuring multiple compositions and
high-index facets have been designed for both theoretical and
experimental studies, revealing that the activity of NPs is de-
ˇ
[a] K. J. Datta, Dr. K. K. R. Datta, Dr. M. B. Gawande, Dr. V. Ranc, Dr. K. CØpe,
Prof. Dr. R. Zboril
Regional Centre of Advanced Technologies and Materials
Department of Physical Chemistry, Faculty of Science
Palacky University in Olomouc
Slechtitelu 27, Olomouc 78371 (Czech Republic)
E-mail: manoj.gawande@upol.cz
Interestingly, these nanoarchitectures displayed superior cat-
alytic activity towards the reduction of olefins, an important re-
action in organic chemistry, which is normally carried out by
using hydrogen gas and heterogeneous transition metal cata-
lysts.[9] Complementary to catalytic hydrogenations with hydro-
gen gas, the use of cost-effective liquid hydrogen donors
(transfer hydrogenation) allows the reduction process under
ambient conditions without the use of high-pressure require-
ment. This is an alluring proposition in terms of safety issues
as the requirement of flammable hydrogen gas (as for gas-
radek.zboril@upol.cz
[b] Dr. V. Malgras, Prof. Y. Yamauchi
World Premier International (WPI) Research Center for Materials
Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)
[c] Prof. R. S. Varma
Sustainable Technology Division, National Risk Management Research
Laboratory, US Environmental Protection Agency
26 West Martin Luther King Drive, MS 443, Cincinnati, Ohio, 45268 (USA)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201503441.
Chem. Eur. J. 2016, 22, 1577 – 1581
1577 ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
core and Pt shell, which further supports the formation of
a highly organized porous core–shell Pd@Pt structure (Fig-
ure 1e–f).
The wide-angle XRD pattern of Pd@Pt exhibits (111), (200),
(220), (311), and (222) reflections that are consistent with the
metallic face-centered-cubic (fcc) structure (see the Supporting
Information, Figure S1a). Most importantly the crystal struc-
tures (fcc) of Pd and Pt are similar with a very high lattice
match (99.23%).[12] The crystallite sizes calculated by Rietveld
refinement are 12 and 3 nm for Pd and Pt NPs, respectively.
Furthermore, selected-area electron diffraction (SAED) pattern
(see the Supporting Information, Figure S1b) displayed rings
assigned to fcc crystal structure, showing the polycrystalline
nature of the Pd@Pt. The metallic nature and zero-valent state
of both Pd and Pt NPs in the Pd@Pt composite were ascer-
tained by X-ray photoelectron spectroscopy (XPS; see the Sup-
porting Information, Figure S1c). The obtained binding ener-
gies at 71.42 and 74.75 eV correspond to 4f7/2 and 4f5/2 states
of metallic Pt, whereas values at 335.73 and 340.99 eV corre-
spond to 3d5/2 and 3d3/2 states of Pd.[13] Finally, the cross-sec-
tional compositional line profiles (see the Supporting Informa-
tion, Figure S2) obtained through line scan confirm the domi-
nant presence of Pd in the aggregate core, with Pt predomi-
nantly located in the surface shell of Pd@Pt nanoparticles. The
atomic ratio of Pd to Pt estimated from atomic absorption
spectroscopy (AAS) was found to be 1:1.
Scheme 1. Schematic illustration of the formation mechanism of Pd@Pt
core–shell NPs.
phase hydrogenation reactions) can be avoided; liquid-phase
hydrogen donors such as formic acid, ethanol, propanol, hy-
drazine hydrate, or ammonium formate can be deployed.[10] An
initial screening on the activity of Pd@Pt core–shell NPs for re-
duction of styrene revealed excellent catalytic activity in the
presence of hydrazine hydrate as a reducing agent. Hydrazine
hydrate is used in many organic syntheses with the only by-
products being water and nitrogen gas.[11]
The size and morphology of the as-prepared samples were
characterized by transmission electron microscopy (TEM). The
catalyst was composed of dandelion-like aggregates with
highly porous structures and sizes ranging from 50–150 nm
(Figure 1a). Importantly, we did not observe any particles with-
The mechanism of formation of the branched morphology
of the Pd@Pt NPs was periodically investigated by time-se-
quential evolution experiments (Figure 2). Initially, NPs without
Figure 1. a) TEM and b) HRTEM images of the Pd@Pt NPs; c) HAADF-STEM
image; d) HRTEM image of the highlighted region in (b); e) HAADF-STEM
image of a single Pd@Pt nanoparticle; f–h) EDS elemental mapping showing
the spatial distributions of Pd (f), Pt (g), and Pd–Pt (h)).
out branched porous structures throughout the sample. A
closer examination of the individual aggregate revealed the
presence of well-defined branched shells (Figure 1b). The high
resolution (HR) TEM image clearly displayed that the NPs have
a spherical core and uniformly branched shells, which was also
observed by high-angle annular dark-field imaging scanning
TEM (HAADF-STEM; Figure 1c and e). The HRTEM of the parti-
cle in the surface shell shows the lattice spacing of 0.22 nm
(Figure 1d), which is commensurate with the (111) plane of the
Pt fcc structure. Nanoscale elemental mapping on the individu-
al aggregate distinctly revealed the uniform distribution of Pd
Figure 2. TEM images of Pd@Pt NPs collected during synthesis, after a) 1;
b) 10; c) 20; d) 30 min.
branches were formed as soon as ascorbic acid was added to
the metallic precursor in the presence of Pluronic P123 (a com-
mercially available triblock copolymer; Figure 2a). After 10 min,
small NPs surrounding the dense core grew into branched
nanostructures (Figure 2b). Further progress in the reaction led
to the formation of highly branched nanostructures, as evident
from the samples collected after 20 and 30 min (Figure 2c,d).
Chem. Eur. J. 2016, 22, 1577 – 1581
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Communication
These observations revealed that the initially formed Pd NP
seeds acted as nucleating centers for the formation of branch-
like Pt nanostructures, reminiscent of structures previously re-
ported by Zhou et al.[14] We envisage that the swift separation
of the Pd core and the Pt shell is due to the different reduction
kinetics of their respective complexes formed with ascorbic
acid. Due to the microscopic irregularities on the surface of the
seeded NPs, the growth of the shell is anisotropic with the tips
growing preferentially, culminating in the formation of
branched nanoarchitectures. In the synthetic procedure, Plur-
onic P123 is crucial in generating the unique branched dande-
lion-like Pd@Pt NPs (see Experimental Section). Replacing P123
by cetyltrimethylammonium bromide (CTAB) produced large ir-
regular aggregates composed of Pt and Pd NPs (see the Sup-
porting Information, Figure S3a). Similarly, replacement of as-
corbic acid with the strong reducing agent sodium borohy-
dride (NaBH4) led to a poor geometrical assembly of Pd–Pt
nanostructures, presumably due to the rapid reduction of
metal species (see the Supporting Information, Figure S3b),
further elucidating the principal role of ascorbic acid in the for-
mation of branched Pd@Pt NPs.
Table 1. Hydrogenation of styrene to ethylbenzene with hydrazine
hydrate as a reducing agent promoted by various catalysts.[a]
Entry
Catalyst
t [h]
Conversion [%][b]
1
2
3[c]
4[c]
5[d]
6[e]
without catalyst
branched Pd@Pt (1:1)
Pd NPs
commercial Pt black
branched Pd@Pt (1:1)
branched Pd@Pt (1:1)
24
0.5
0.5
0.5
2
5
100
9
4
6
2
0
[a] Reaction conditions (unless otherwise stated): styrene (0.14 mmol), cat-
alyst (2 mg), N2H4·H2O (20 mL), aqueous NH3 (10 mL, 28–30%), ethanol
(1 mL), 608C; [b] conversion degree determined by gas chromatography;
[c] catalyst (1 mg); [d] 2-propanol as hydrogen source; [e] without hydra-
zine hydrate.
Table 2. Reduction of various olefins catalyzed by Pd@Pt.[a]
Entry Substrate
Product
Conversion
[%][b]
Yield
[%]
1
2
100
100
95
96
We next examined the catalytic efficacy of branched porous
Pd@Pt NPs for the reduction of various olefins using hydrazine
hydrate as a reducing agent at room temperature (Scheme 2).
3
4
5
100
81
82
90
100[c]
100
Scheme 2. Olefin reduction catalyzed by Pd@Pt NPs.
The method has been found to have several advantages,
such as low catalyst loading, shorter reaction times, and high
product selectivity as compared to previously reported proce-
dures.[9a] In preliminary experiments, styrene was selected as
a model substrate to optimize the reaction conditions. There
was no appreciable reaction in the absence of catalyst (Table 1,
entry 1). To compare the expected superior catalytic efficiency
of the branched Pd@Pt NPs (Table 1, entry 2), commercially
available Pt black and Pd NPs were employed for the reaction,
using the same weight amount of NPs with hydrazine hydrate
as hydrogen donor. It was noted that reaction remained in-
complete, giving conversions of only 9% with Pd NPs and 4%
with Pt black (Table 1, entries 3 and 4). Additionally, we investi-
gated 2-propanol as a hydrogen donor. However, negligible
conversion was obtained (Table 1, entry 5). Similarly, in the ab-
sence of hydrazine hydrate no conversion was registered
(Table 1, entry 6). Thus, hydrazine hydrate was established as
the best hydrogen source, when compared to 2-propanol in
terms of conversion.
6
97[d]
85
[a] Reaction conditions: Substrate (0.14 mmol), catalyst (2 mg), N2H4·H2O
(20 mL), aqueous NH3 (10 mL, 28–30%), ethanol (1 mL), 608C for 30 min;
[b] determined by gas chromatography; [c] at t=60 min; [d] 94% ethyl-
benzene and 3% styrene after 60 min.
excellent conversions and yields (Table 2, entries 2–4), as was
trans-stilbene (Table 2, entry 5). The reaction of phenylacety-
lene with hydrazine hydrate under the present experimental
conditions afforded ethylbenzene as the major product along-
side a very small amount of styrene (Table 2, entry 6).
Having already assessed the efficacy of Pd NPs and Pt black
in the reduction of styrene as a model reaction (9% and 4%
conversion, respectively; Table 1, entries 3 and 4), we also com-
pared the catalytic activity of the developed branched core–
shell Pd@Pt NPs with that of physically mixed Pd NPs and Pt
black (Pd/Pt=1:1) under the same reaction conditions
(Figure 3). Whereas the individual metal components gave very
poor conversions, we observed 20% conversion for the physi-
cally mixed Pd and Pt, in comparison to 100% conversion with
With optimized reaction conditions in hand, the substrate
scope was examined. A variety of olefins bearing electron-with-
drawing (4-fluoro, 3-nitro) or electron-donating (4-methoxy)
substituents, were reduced to their corresponding products in
Chem. Eur. J. 2016, 22, 1577 – 1581
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Communication
showed that the developed branched core–shell Pd@Pt NPs
stand out as the best candidate in terms of conversion, owing
to synergetic effects of the combination of Pd and Pt. We be-
lieve that unique micro–mesoporous structure, with a high
contribution from mesopores, is one of the key parameters re-
sponsible for the superior catalytic activity. Indeed, we envis-
age the applicability of Pd@Pt nanoarchitectures as a promising
material for various catalytic organic transformations, energy
storage and fuel-cell technologies.
Experimental Section
Figure 3. Comparison of the degree of conversion in the hydrogenation of
styrene to ethylbenzene with Pt black, Pd NPs, a physical mixture of Pd and
Pt NPs (1:1), and branched core–shell Pt@Pd NPs (1:1).
Typical synthesis of Pd@Pt core–shell NPs
To a stirred solution of K2PtCl6 (17.5 mm), Na2PdCl4 (2.5 mm), and
Pluronic P123 (1.74 mm) in water (5 mL) was quickly added 0.1m
ascorbic acid (AA, 5 mL) and the resultant mixture was stirred for
30 min at room temperature. The color of the solution immediately
changed from transparent brownish to dark brownish-red and fi-
nally to opaque black. After 30 min of reaction, the product was
isolated and residual Pluronic P123 was removed by centrifugation
at 8000 rpm for 20 min, followed by three consecutive washing/
centrifugation cycles with water (120 mL). The collected product
was dried at 508C and/or redispersed in water by sonication to
produce a colloidal suspension for further characterization.
the Pd@Pt NPs. The Pd@Pt NPs’ markedly higher catalytic activ-
ity than those of Pd NPs, Pt black and Pd+Pt NPs indicating
the significant synergistic effects between the Pd core and Pt
shell (Figure 3).
The improvement of the catalytic function of Pt catalysts by
alloying with Pd is well known and has been reported in the
literature[4c,15] In the case of the core–shell (not alloyed) sys-
tems, the situation is quite different; core and shell elements
play a critical role in determining the catalytic activity of the
composite, as they can alter the binding energy of reaction in-
termediates on the NP surface.[16] In addition, the effect of the
surface area and the pore sizes of such hybrid systems needs
to be stated, which might be among the major contributors in
determining the catalytic activity because of the better trans-
port of reactants/products. These parameters could be respon-
sible for the extraordinary catalytic efficiency of the branched
core–shell Pd@Pt NPs. Nitrogen adsorption–desorption iso-
therms and pore size distributions of the branched Pd@Pt NPs,
Pd NPs, and commercial Pt black are given in the Supporting
Information (Figure S4). The branched Pd@Pt NPs are shown to
have a unique micro–mesoporous structure with a principal
contribution of mesopores having sizes in tens of nanometers.
Any mesoporous structure is considerably less developed or
even absent for individual samples of Pd and Pt NPs. Thus, the
considerably higher surface area and unique distribution of
mesopores in the Pd@Pt catalyst, compared to Pd NPs and Pt
black, offer better mass transport, which ultimately results in
higher catalytic activity.
Acknowledgements
The authors thank Ms. J. Straska for TEM, Mr. M. Petr for XPS,
Dr. C. Aparicio for XRD, Mr. M. Krizek for porosity and adsorp-
tion–desorption measurements, and Dr. J. Tucek for technical
assistance. The authors acknowledge support from the Ministry
of Education, Youth and Sports of the Czech Republic (LO1305)
and the Operational Program Education for Competitiveness:
European Social Fund (projects CZ.1.07/2.3.00/30.0041 and
CZ.1.07/2.3.00/30.0004).
Keywords: core–shell nanoparticles · heterogeneous catalysis ·
olefins · palladium · platinum reduction
[1] a) A. C. Chen, P. Holt-Hindle, Chem. Rev. 2010, 110, 3767–3804; b) X. Q.
Huang, Y. J. Li, Y. Chen, E. B. Zhou, Y. X. Xu, H. L. Zhou, X. F. Duan, Y.
Huang, Angew. Chem. Int. Ed. 2013, 52, 2520–2524; Angew. Chem.
2013, 125, 2580–2584.
[2] a) S. E. Habas, H. Lee, V. Radmilovic, G. A. Somorjai, P. Yang, Nat. Mater.
2007, 6, 692–697; b) L. Wang, Y. Yamauchi, J. Am. Chem. Soc. 2009, 131,
9152–9153; c) B. Lim, Y. N. Xia, Angew. Chem. Int. Ed. 2011, 50, 76–85;
Angew. Chem. 2011, 123, 78–87.
[3] a) M. B. Gawande, A. Goswami, T. Asefa, H. Guo, D.-L. Peng, A. Biradar, R.
Zboril, R. S. Varma, Chem. Soc. Rev. 2015, 44, 7540–7590; b) R. Ghosh
Chaudhuri, S. Paria, Chem. Rev. 2012, 112, 2373–2433; c) C. Burda, X. B.
Chen, R. Narayanan, M. A. El-Sayed, Chem. Rev. 2005, 105, 1025–1102;
d) X. W. Liu, X. G. Liu, Angew. Chem. Int. Ed. 2012, 51, 3311–3313;
Angew. Chem. 2012, 124, 3367–3369; e) Y. Ding, F. R. Fan, Z. Q. Tian,
Z. L. Wang, J. Am. Chem. Soc. 2010, 132, 12480–12486.
[4] a) D. S. Wang, Y. D. Li, Adv. Mater. 2011, 23, 1044–1060; b) H. Yang,
Angew. Chem. Int. Ed. 2011, 50, 2674–2676; Angew. Chem. 2011, 123,
2726–2728; c) H. Zhang, M. S. Jin, Y. N. Xia, Chem. Soc. Rev. 2012, 41,
8035–8049; d) F. Zaera, Chem. Soc. Rev. 2013, 42, 2746–2762; e) Q.
Zhang, I. Lee, J. B. Joo, F. Zaera, Y. D. Yin, Acc. Chem. Res. 2013, 46,
1816–1824; f) H. Wang, L. Y. Chen, Y. H. Feng, H. Y. Chen, Acc. Chem.
In summary, a facile one-pot aqueous synthetic method has
been developed for the assembly of highly branched micro–
mesoporous Pd@Pt core–shell NPs with unique dandelion-like
morphology. This unique catalytic system could be achieved
by the sequential formation of the Pd core followed by a Pt
shell, owing to differences in their reduction kinetics associated
with the use of ascorbic acid as a weak reducing agent. A wide
range of functionalized olefins, such as 4-fluorostyrene and 4-
methoxystyrene, were reduced in good to excellent yields by
the branched Pd@Pt core–shell NPs with hydrazine hydrate as
a hydrogen donor. The comparison of catalytic efficiency with
individual metals (Pd NPs and commercial Pt black) and their
physical mixture (Pd/Pt=1:1) for the reduction of styrene
Chem. Eur. J. 2016, 22, 1577 – 1581
www.chemeurj.org
1580 ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Res. 2013, 46, 1636–1646; g) S. G. Zhou, K. McIlwrath, G. Jackson, B.
Eichhorn, J. Am. Chem. Soc. 2006, 128, 1780–1781.
[5] a) Y. J. Li, Z. W. Wang, C. Y. Chiu, L. Y. Ruan, W. B. Yang, Y. Yang, R. E.
Palmer, Y. Huang, Nanoscale 2012, 4, 845–851; b) B. Lim, J. G. Wang,
P. H. C. Camargo, M. J. Jiang, M. J. Kim, Y. N. Xia, Nano Lett. 2008, 8,
2535–2540.
[6] a) J. W. Hong, S. W. Kang, B. S. Choi, D. Kim, S. B. Lee, S. W. Han, ACS
Nano 2012, 6, 2410–2419; b) H. Zhang, Y. J. Yin, Y. J. Hu, C. Y. Li, P. Wu,
S. H. Wei, C. X. Cai, J. Phys. Chem. A J. Phys. Chem. B J. Phys.Chem. C.
2010, 114, 11861–11867.
[7] a) P. P. Zhang, Y. B. Hu, B. H. Li, Q. J. Zhang, C. Zhou, H. B. Yu, X. J.
Zhang, L. Chen, B. Eichhorn, S. H. Zhou, ACS Catal. 2015, 5, 1335–1343;
b) B. Lim, M. J. Jiang, P. H. C. Camargo, E. C. Cho, J. Tao, X. M. Lu, Y. M.
Zhu, Y. N. Xia, Science 2009, 324, 1302–1305; c) M. J. Jiang, B. Lim, J.
Tao, P. H. C. Camargo, C. Ma, Y. M. Zhu, Y. N. Xia, Nanoscale 2010, 2,
2406–2411; d) H. Zhang, M. S. Jin, J. G. Wang, M. J. Kim, D. R. Yang, Y. N.
Xia, J. Am. Chem. Soc. 2011, 133, 10422–10425; e) B. Lim, J. G. Wang,
P. H. C. Camargo, C. M. Cobley, M. J. Kim, Y. N. Xia, Angew. Chem. Int. Ed.
2009, 48, 6304–6308; Angew. Chem. 2009, 121, 6422–6426; f) Y. Liu,
M. F. Chi, V. Mazumder, K. L. More, S. Soled, J. D. Henao, S. H. Sun, Chem.
Mater. 2011, 23, 4199–4203; g) H. Kobayashi, M. Yamauchi, H. Kitagawa,
Y. Kubota, K. Kato, M. Takata, J. Am. Chem. Soc. 2008, 130, 1818–1819;
h) S. F. Xie, S. I. Choi, N. Lu, L. T. Roling, J. A. Herron, L. Zhang, J. Park,
J. G. Wang, M. J. Kim, Z. X. Xie, M. Mavrikakis, Y. N. Xia, Nano Lett. 2014,
14, 3570–3576; i) Y. Wang, N. Toshima, J. Phys. Chem. B 1997, 101,
5301–5306.
[10] a) R. V. Jagadeesh, G. Wienhofer, F. A. Westerhaus, A. E. Surkus, H. Junge,
K. Junge, M. Beller, Chem. Eur. J. 2011, 17, 14375–14379; b) S. Horn, C.
Gandolfi, M. Albrecht, Eur. J. Inorg. Chem. 2011, 2863–2868; c) S. Gladia-
li, E. Alberico, Chem. Soc. Rev. 2006, 35, 226–236; d) P. S. Kumbhar, J.
Sanchez-Valente, J. M. M. Millet, F. Figueras, J. Catal. 2000, 191, 467–
473; e) S. M. Auer, J. D. Grunwaldt, R. A. Koppel, A. Baiker, J. Mol. Catal.
A 1999, 139, 305–313; f) R. Kadyrov, T. H. Riermeier, Angew. Chem. Int.
Ed. 2003, 42, 5472–5474; Angew. Chem. 2003, 115, 5630–5632.
[11] a) M. Benz, R. Prins, Appl. Catal. A 1999, 183, 325–333; b) Y. J. Gao, D.
Ma, C. L. Wang, J. Guan, X. H. Bao, Chem. Br. Chem.Commun. 2011, 47,
2432–2434; c) A. K. Jain, Synlett 2004, 2445–2446; d) M. Lauwiner, P.
Rys, J. Wissmann, Appl. Catal. A 1998, 172, 141–148; e) P. G. Ren, D. X.
Yan, X. Ji, T. Chen, Z. M. Li, Nanotechnology 2011, 22, 055705; f) U.
Sharma, P. Kumar, N. Kumar, V. Kumar, B. Singh, Adv. Synth. Catal. 2010,
352, 1834–1840.
[12] a) L. Wang, Y. Yamauchi, J. Am. Chem. Soc. 2013, 135, 16762–16765;
b) H. Ataee-Esfahani, M. Imura, Y. Yamauchi, Angew. Chem. Int. Ed. 2013,
52, 13611–13615; Angew. Chem. 2013, 125, 13856–13860.
[13] Y. Z. Lu, Y. Y. Jiang, W. Chen, Nano Energy 2013, 2, 836–844.
[14] Y. X. Zhou, D. S. Wang, Y. D. Li, Chem. Commun. 2014, 50, 6141–6144.
[15] H. J. Lee, S. E. Habas, G. A. Somorjai, P. D. Yang, J. Am. Chem. Soc. 2008,
130, 5406–5407.
[16] a) R. Choi, S. I. Choi, C. H. Choi, K. M. Nam, S. I. Woo, J. T. Park, S. W. Han,
Chem. Eur. J. 2013, 19, 8190–8198; b) P. Strasser, S. Koh, T. Anniyev, J.
Greeley, K. More, C. F. Yu, Z. C. Liu, S. Kaya, D. Nordlund, H. Ogasawara,
M. F. Toney, A. Nilsson, Nat. Chem. 2010, 2, 454–460; c) W. J. Tang, G.
Henkelman, J. Chem. Phys. 2009, 130, 194504.
[8] a) L. Wang, Y. Nemoto, Y. Yamauchi, J. Am. Chem. Soc. 2011, 133, 9674–
9677; b) L. Wang, Y. Yamauchi, J. Am. Chem. Soc. 2010, 132, 13636–
13638; c) L. Wang, Y. Yamauchi, Chem. Mater. 2011, 23, 2457–2465.
[9] a) A. Dhakshinamoorthy, S. Navalon, D. Sempere, M. Alvaro, H. Garcia,
Chem. Commun. 2013, 49, 2359–2361; b) C. Smit, M. W. Fraaije, A. J.
Minnaard, J. Org. Chem. 2008, 73, 9482–9485.
Received: August 29, 2015
Published online on November 13, 2015
Chem. Eur. J. 2016, 22, 1577 – 1581
www.chemeurj.org
1581 ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim