11:41am Friday 06 December 2019

Platinum nanocatalyst could aid drugmakers

Nanoparticles combining platinum and gold act as superefficient
catalysts, but chemists have struggled to create them in an
industrially useful form. Rice University chemists have answered the
call this week with a polymer-coated version of gold-platinum nanorods,
the first catalysts of their kind that can be used in the organic
solvents favored by chemical and drug manufacturers.

The research is available online in the Sept. 1 issue of the German scientific journal Angewandte Chemie International Edition.

Catalysts are compounds that speed up or slow down chemical
reactions without being consumed by them. An everyday example would be
the catalytic converters that help breakdown toxic components of
automotive exhaust. The chemical and drug industries spend billions of
dollars each year for catalysts that are needed to process drugs and
other high-value chemicals.

“There are some industrial reactions where drugmakers have no choice
but to use platinum and palladium catalysts, but the majority of these
are homogenous, which means they mix readily with reactants and are
very difficult to remove,” said lead researcher Eugene Zubarev,
associate professor in chemistry at Rice. “Because these heavy metals
are toxic, they must be completely removed from the drug after its
synthesis is completed. However, the removal of homogeneous catalysts
is very time-consuming and expensive, which creates a big problem for
pharmaceutical companies.”

Among catalysts, platinum and palladium are prized for reactions
involving hydrogen because atoms of hydrogen typically join together in
pairs, and platinum and palladium are particularly good at cleaving
these pairs and leaving the individual hydrogen atoms available for
reactions with other molecules.

Zubarev and Rice graduate student Bishnu Khanal, who will soon start
his postdoctoral research at Los Alamos National Laboratory, set out to
make a heterogeneous platinum catalyst that was soluble enough for
industrial use, but that could also be easily removed.

Previous studies had shown that combining platinum with gold in tiny
nanoparticles could enhance the platinum’s catalytic effect, so Zubarev
and Khanal started with tiny rods of pure gold and coated them with a
layer of platinum so thin that it left the gold exposed in some places.

After confirming the structure of the gold-platinum nanorods,
Zubarev and Khanal had to find a way to make them soluble in organic
solvents that are favored by industry. Building on Zubarev’s previous
work in making soluble gold nanorods, the pair found a way to attach
hair-like molecules of polystyrene to the surface of the gold-platinum

Zubarev and Khanal found the coated particles were easy to remove
from solution with a conventional centrifuge. In addition, the
polystyrene shells made them completely soluble in organic solvents and
dramatically enhanced their catalytic selectivity.

“The selectivity of the coated gold and platinum nanorods will be
very attractive to industry,” Zubarev said. “For example, we found they
had nearly 100 percent catalytic selectivity for the hydrogenation of
terminal olefins.”

Zubarev’s group is using similar methods to produce gold-palladium
catalysts in a follow-up study. Palladium is another high-demand
catalyst. “The early indications are very promising,” he said.

The research is supported by the National Science Foundation, the Robert A. Welch Foundation and the Alfred Sloan Foundation.

CONTACT: Jade Boyd
PHONE: 713-348-6778

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