selective oxidation processes that are used to make
compounds contained in agrochemicals, pharmaceuticals
and other chemical products can be accomplished more
cleanly and more efficiently with gold nanoparticle
catalysts, researchers have reported in Nature magazine.
A team of 13 U.K. researchers and one U.S. researcher
reported in the Oct. 20 issue of the British journal
that the carbon-supported gold catalysts can be fine-tuned
with high selectivity for desired products through
the addition of trace amounts of bismuth.
The gold catalysts can also carry out partial oxidations
under solvent-free conditions, the researchers said,
making them more environmentally friendly than oxidation
processes that use chlorine, and less costly than
those employing organic peroxides.
The team, led by Graham Hutchings, professor of
physical chemistry at Cardiff University in Wales,
included eight other Cardiff chemists, four scientists
from the Johnson Matthey chemical company in the
United Kingdom, and a materials scientist from Lehigh
University in Bethlehem, Pennsylvania.
article was titled "Tuneable gold catalysts
for selective hydrocarbon oxidation under mild conditions."
Haruta, a catalyst chemist at Tokyo Metropolitan
University who has been at the forefront of gold
nanoparticles research for more than a decade, said
in a commentary accompanying the Nature article that
the breakthrough by Hutchings's group had the potential
to "transform" the chemical industry.
that most industrial oxidation processes use chlorine
or organic peroxides, Haruta said, "the
chemical industry would be transformed if selective
oxidation of hydrocarbons could be achieved efficiently
using cheap and clean oxygen from the air. The advancement
by Hutchings and colleagues of 'greener' methods
for oxidation catalysis using gold is therefore invaluable."
The industrial selective oxidation processes that
Hutchings's team catalyzed with gold nanoparticles
are used to convert unsaturated hydrocarbons to oxygen-containing
organic compounds (e.g., epoxides, ketones), which
in turn serve as higher-value compounds that form
the basis for many chemical products.
The challenge, says Chris Kiely, professor of materials
science and engineering at Lehigh University, is
to selectively insert an oxygen atom at specific
positions into long-chain or cyclic-ring hydrocarbon
carbon molecules, something which nanoparticulate
gold achieves effectively.
The gold nanoparticles, which measure 2 to 15 nanometers
in width (1 nm equals one one-billionth of a meter)
must be distributed evenly over a large surface area
support and prevented from coalescing and forming
larger particles with weaker catalytic properties.
"The nano-gold catalyst can effectively aid the
insertion of an oxygen atom into the unsaturated
hydrocarbon," says Kiely, who has co-authored several
dozen papers with Hutchings. "Activated carbon provides
a viable support for the nanoparticles. The gold
catalyst can also be fine-tuned and made more effective,
giving a higher yield of epoxides and ketones, with
the addition of occasional atoms of bismuth.
trying to determine the size, distribution and
shape of the gold nanoparticles, and to see how
these parameters relate to the measured catalytic
properties. We are also interested in the interaction
of gold with other promoter elements, such as bismuth,
and we're trying to identify exactly where the bismuth
atoms are going and why they have a beneficial effect."
Kiely, who joined the Lehigh faculty in 2002 after
serving on the materials science and engineering
and chemistry faculties at Liverpool University,
uses transmission electron microscopy and various
spectroscopic techniques to characterize the gold
The recent acquisition by Lehigh University of two
aberration-corrected electron microscopes, including
a JEOL 2200FS transmission electron microscope, will
shed more light on future work in the area of gold
catalysis, he said.
we were able to see nanoparticles and achieve atomic
resolution, but not with the same degree of clarity
that the new JEOL microscope provides. The new
instrument also gives us the capability of doing
chemical composition analysis with close to atomic
column precision, which will be a big boon."
Gold in recent years has drawn more attention from
researchers as a potential catalyst in chemical processing,
pollution control and fuel cell applications. Haruta,
a pioneer in this area, demonstrated a decade ago
that gold nanoparticles could be used, amongst other
things, as catalysts to de-odorize restrooms and
to convert carbon monoxide to carbon dioxide at low
But much remains to be learned for nano-gold to
realize its full potential, says Kiely, who directs
the Nanocharacterization Laboratory in Lehigh's Center
for Advanced Materials and Nanotechnology.
"Gold is a very useful catalyst for many chemical
reactions," says Kiely, "but we're still not sure
what happens at the molecular scale during the catalysis
process. The more we learn, the better we can fine-tune
gold nanoparticle catalysts."
Contact: Kurt Pfitzer