CHEMIST RY
QUESTION How does chemistry change at the nanoscale? Can a
catalysts,” where a catalytically active material such as
single atom drive a catalytic reaction?
platinum is dispersed in the form of nanoparticles on
“As the size of particles of materials is reduced
Nanoscale Chemistry: Every Atom Counts SCOTT ANDERSON
One main class of catalysts is “supported
a support material, like carbon or a metal oxide. This
to less than 20 nanometers, the physical properties
technique maximizes the available surface area of the
begin to change, and this affects chemistry as well,”
expensive material, but if the nanoparticles are small
says Scott L. Anderson, Distinguished Professor of
enough, the size also begins to “tune” the chemical
Chemistry at the U.
properties of the catalytic particles, allowing new
For example, the electronic and geometric structure of nanoparticles is different from the bulk
approaches to catalyst optimization. “In one case, we are exploring the physical and
structure of materials. Changing geometric structure
catalytic properties of small metal clusters containing
can include changes in chemical bond lengths and
between one and 30 metal atoms, supported on
in the shape of surface sites, and both factors affect
carbon substrates. In such extremely small clusters,
chemical reactivity.
the properties can change dramatically if the
“Chemistry is all about electrons being shared between reactants, so if the electronic properties of nanoparticles are different, this affects the kinds of chemistry they can undergo,” says Anderson.
cluster size is changed by just one or two atoms,” says Anderson. For example, in ethanol electro-oxidation, catalyzed by platinum clusters, the activity varies by an order of magnitude for clusters in the one- to
WHO Anderson is currently investigating several fundamental questions, all relating to nanoparticle surface chemistry and catalytic reactions. Catalysts work by selectively lowering the
20-atom size range, with Pt4 (a platinum cluster with 4 atoms) and Pt10 being particularly active, and Pt1, Pt7, and Pt8 being almost inert. “That is of some interest from a practical perspective, but it also provides an opportunity to
energy barriers that normally inhibit specific chemical
use size effects to probe the reaction mechanism
reactions, thus reducing the energy and cost involved
itself,” says Anderson.
and improving the selectivity toward desired products, all while minimizing by-products.
“Working together with a theory collaborator at UCLA, Professor Anastassia Alexandrova, we are preparing and studying alloy clusters where the
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