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)
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-
[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
Chem. Eur. J. 2016, 22, 1577 – 1581
1577 ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim