Chemical Engineering October 2012 - 14

CHEMENTATOR
A wall-less vessel
A nano cage made from a stack of benzenes
P
rofessor Kenichoro Itami and his group
at Nagoya University (synth.chem.
nagoya-u.ac.jp) have synthesized a cage-type
carbon nano-molecule, Carbon Nano-cage,
composed of 20 condensed benzene rings -
C120H78. The group used a procedure it developed
four years ago to synthesize carbon
nano-rings with the ability to eliminate the
distortion of ring-type benzene structures
during synthesis steps. First, they synthesized
an unstrained cyclic precursor by assembling
six L-shaped units [cis-di(p-bromophenyl)cyclohexane
derivative] and two
three-way units (1,3,5-triborylbenzene) by
cross- and homo-coupling reactions. Then,
they obtained carbon nano-cages through
acid-mediated aromatization of the cyclohexane
moieties in the precursor.
The nano-cage is a white solid that is
soluble in almost all organic solvents and
stable at temperatures up to 300°C. It
has a 1.8-nm inner diameter, which could
confine a guest molecule. In collaboration
with the National Institute of Advanced
Industrial Science and Technology, the researchers
found that the carbon nano-cage
has a large two-photon absorption cross
section and a high fluorescence quantum
yield of 87%. These properties are advantageous
for such applications as organic
electroluminescent and organic transistor
materials, optical recording materials, for
high-density light storage, fluorescence
imaging of bio-molecules and light sensing
(using a guest molecule). The structural
characteristics of the C120H78 cage make
it suitable as a backbone structure that
could be applied for the bottom-up synthesis
of branched carbon nanotubes, or as
a junction unit of branched carbon nanotubes,
which could be applied as miniscule
transistors and logic gates.
A little gold can reduce the Pt loading in fuel cells
A
challenge in the development of
polymer-electrolyte membrane fuel
cells is the durability and electrocatalytic
activity of platinum-based
electrocatalysts. The sluggishness of
the oxygen reduction reaction (ORR)
causes the fuel cell performance to be
limited by the cathodic reaction, and
a high Pt loading is required for the
cathode catalyst to achieve good activity
for the ORR.
Now researchers from the Institute
of Bioengineering and Nanotechnology
(IBN; Singapore: www.ibn.a-star.
Scientists at the U.S. Dept. of
Energy's Argonne National Laboratory
(Ill.; www.anl.gov) have
discovered a way to levitate individual
droplets of solutions containing
different pharmaceuticals
- a technique that may help in
the development of more efficient
drugs. By eliminating the vessel
walls - where compounds typically
crystallize - the researchers
are hoping to better understand
the formation of amorphous solids
as the solvent evaporates. Most
drugs are crystalline, so they don't
get fully absorbed by the body,
says Argonne's Chris Benmore.
who leads the study.
The scientists use an acoustic
levitator to study how droplets
evaporate without touching
anything. The droplet is placed
at the node of standing waves,
which are generated by two opposed
speakers. The acoustic
pressure from the sound waves
is sufficient to cancel the effect of
gravity. The system allows in-situ
analysis with the high-energy
X-Ray beam at Argonne's Advanced
Photon Source. ❏
edu.sg), led by IBN executive director,
professor Jackie Y. Ying, have discovered
that by replacing the central part
of the catalyst with a gold-copper alloy
and leaving just the outer layer in
platinum, a superior electrocatalytic
activity and excellent stability toward
the ORR are achieved.
The researchers reported the synthesis
of core-shell AuCu@Pt nanoparticles by
depositing Pt on preformed AuCu-alloy
nanoparticles in oleylamine. The AuCu
alloy core has a slightly smaller lattice
parameter than Pt, creating a benefiNew
catalysts for Baeyer-Villiger oxidation reactions
K
azuaki Ishihara and his group at
Nagoya University (Japan; www.
ishihara-lab.net) have established a
new, environment friendly reaction
technology - using Baeyer-Villiger
oxidations - for selectively oxidizing
ketones into esters. The reaction
uses hydrogen peroxide as the oxidant,
and has potential as a safer alternative
to the conventional industrial
route for making the nylon precursor
-caprolactam from -caprolactone. Instead
of H2O2, industrial routes have
used acetyl hydroperoxide for making
-caprolactam, which required very
careful handling of explosive acetyl
cial compressive strain effect on the Pt
shell. In contrast, a tensile strain effect
would be induced by depositing Pt on a
core of Au - which has a larger lattice
parameter than Pt - leading to a lower
catalytic activity. In addition to the stabilization
effect exerted by the alloy core
on the Pt shell during the ORR, using
the alloy also reduces the Pt loading in
the resulting electrocatalyst.
The catalytic activity of AuCu@Pt was
0.571 A/mg of Pt, which was more than
five times higher than that of commercial
Pt catalysts.
hydroperoxide, and also purification
steps for removing byproducts and
the corrosive, smelly residual catalyst
after the reaction.
The new route uses hydrogen peroxide
with an effective oxidation-acceleration
catalyst system, both of which are
easier to handle, and no byproducts are
produced. The researchers found that
two environmentally friendly catalysts
- lithium tetrakis(pentafluorophenyl)
borate or Li[B(C6F5)4], and calcium
tetrakis(pentafluorophenyl) or
Ca[B(C6F5)4] - can be used in both
hydrophilic systems with H2O2 as the
oxidant, and in lipophilic systems, in14
CHEMICAL ENGINEERING WWW.CHE.COM OCTOBER 2012
cluding those with ketone substrates
and ester products. These catalysts selectively
oxidize the C=O group, even if
the substrate contains groups that are
sensitive to oxidation.
In laboratory trials, the researchers
produced -caprolactone from cyclohexanone
with 80% yield after 2
h agitation at 70°C, using H2O2 with
Ca[B(C6F5)4] as the oxidation catalyst
system. They also obtained the lactone
from 2-adamantanone with 98% yield
after 10 h agitation at 70°C using the
oxidation catalyst system of hydrogen
peroxide, Ca[B(C6F5)4], and oxalic acid
as a promoter.
http://www.anl.gov http://nagoya-u.ac.jp http://www.edu.sg http://www.ibn.a-star http://www.ishihara-lab.net http://WWW.CHE.COM
Chemical Engineering October 2012

Table of Contents for the Digital Edition of Chemical Engineering October 2012
