Scientists at the U.S. Department
of Energy's Argonne National Laboratory have identified a new class
of silver-based catalysts for the production of the industrially useful chemical
propylene oxide that is both environmentally friendly and less expensive.
“The production of propylene oxide has a significant amount of by-products
that are harmful to the environment, including chlorinated or peroxycarboxylic
waste,” said chemist Stefan Vajda of Argonne's Materials Science
Division and Center for Nanoscale Materials. “We have identified nanoclusters
of silver as a catalyst that produce this chemical with few by-products at low
Propylene oxide is commonly used in the creation of plastics and propylene
glycols for paints, household detergents and automotive brake fluids.
The study is a result of a highly collaborative team that involved five Argonne
divisions and collaborators from the Fritz-Haber-Institut in Berlin and from
the University of Illinois at Chicago, including a collaboration between the
experimental effort led by Stefan Vajda and the theoretical analysis led by
materials chemist Larry Curtiss and nanoscientist Jeff Greeley.
Large silver particles have been used to produce propylene oxide from propylene,
but this method suffers from a low selectivity or low conversion to propylene
oxide—creating a large amount of carbon dioxide. Vajda discovered that
nanoscale clusters of silver, consisting of both three-atom clusters as well
as larger clusters of 3.5 nanometers in size, are highly active and selective
catalysts for the production of propylene oxide.
Curtiss and Greeley then modeled the underlying mechanism behind why these
ultrasmall nanoparticles of silver were so effective in creating propylene oxide.
They discovered that the open shell electronic structure of the silver catalysts
was the impetus behind the nanoclusters' selectivity.
“Propylene oxide is a building block in the creation of several other
industrially relevant chemicals, but the current methods of creating it are
not efficient,” Curtiss said. “The work opens a new chapter in the
field of silver as a catalyst for propene epoxidation.”
“This is basically a holy grail reaction,” said Greeley.
Funding for this project was provided by the U.S. Department of Energy Office
of Science and from the U.S. Air Force Office of Scientific Research. A paper
on this work will be published in the April 9 issue of the journal Science.