Ultrasonics Sonochemistry 17 (2010) 26–29
Ultrasonics Sonochemistry
Short Communication
Selective hydrogenation by polymer-encapsulated platinum nanoparticles prepared
by an easy single-step sonochemical synthesis
*
Mahito Atobe , Mayuko Okamoto, Toshio Fuchigami, Jong-Eun Park
Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Technology, Tokyo Institute of Technology, 4259-G1-3 Nagatsuta,
Midori-ku, Yokohama 226-8502, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Polypyrrole-encapsulated platinum nanoparticles (PPy/Pt-NPs) prepared by an easy single-step sono-
chemical synthesis were used as catalysts for the liquid phase hydrogenation of substituted alkenes in
methanol or methanol/water mixtures. Polypyrrole (PPy) coatings on the nanoparticles were able to
act as nanoscopic filters for substrates molecules, and consequently substrate selectivity could be con-
trolled in the catalytic processes.
Received 15 April 2009
Received in revised form 29 May 2009
Accepted 2 June 2009
Available online 6 June 2009
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Polypyrrole
Nanoparticle
Sonochemical synthesis
Hydrogenation
Substituted alkene
1. Introduction
synthesized by one-step sonochemical operation are highly selec-
tive catalysts.
Metal nanoparticles are attractive for catalysis because their
large surface area-to-volume ratio allows effective utilization of
expensive metals [1,2]. Moreover, the nanoparticles show unique
catalytic properties different from those of bulk metals [3]. How-
ever, the naked nanoparticles tend to aggregate, and consequently
the excellent catalytic properties would be impaired [4]. To resolve
this problem, catalytic nanoparticles have been stabilized by cap-
ping with ligands such as polymer [5–7] and dendrimer [8]. Fur-
thermore, these ligands are also able to act as nanoscopic filters
for substrates molecules, and consequently substrate selectivity
and overall catalytic reactivity can be controlled in the catalytic
processes [9–11].
In our previous work, we successfully prepared polypyrrole-
encapsulated gold or platinum nanoparticles by one-step sono-
chemical operation [12,13]. These composite materials could be
easily obtained only by ultrasonication to an aqueous solution con-
taining pyrrole monomer, the corresponding metal ion, and stabi-
lizer (Scheme 1).
2. Experimental
2.1. Materials
All chemicals were used without further purification. Distilled
methanol and deionized water were used as solvents for syntheses
of the nanoparticles and hydrogenation reactions.
2.2. Sonochemical synthesis of Pt-NPs and PPy/Pt-NPs
Sonochemical synthesis of Pt-NPs and PPy/Pt-NPs and their
characterizations were reported in Ref. [13]. H2PtCl6Á6H2O was dis-
solved in distilled water to make 0.15 mmol dmÀ3 solutions in the
absence or the presence of 10 mM pyrrole, and SDS (1.25 mM) was
added as a stabilizer. The H2PtCl6Á6H2O solution containing SDS
was placed in a water bath. Because the local heating produced
by the cavitation also depends on the solution temperature, the
temperature of the water bath during the sonication was held at
298 0.5 K unless otherwise mentioned. Ultrasonic irradiation
was performed with a collimated 20 kHz beam from a ceramic
We envision that polypyrrole-encapsulating catalyst like metal
nanoparticles may act as selective gates that control the access of
small molecules to the embedded catalysts. Using hydrogenation
as a model process, we demonstrate in this communication that
polypyrrole-encapsulated platinum nanoparticles (PPy/Pt-NPs)
transducer with a titanium amplifying horn (13 mm
U, Branson
Sonifier 450D) directly immersed in the solution and operated with
an input power of 22.6 W cmÀ2. After the sonication for 4 h, the
colloidal suspensions were centrifuged at 2000 rpm for 30 min
and separated as sediments. The sediments were rinsed with
* Corresponding author. Fax: +81 45 924 5407.
1350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.06.002