Argonne, Illinois -- Scientists at the US Department of Energy's Argonne National Laboratory have identified a class of silver-based catalysts for the production of propylene oxide, which they claim is less expensive than traditional catalysts as well as being environmentally friendly.
"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 temperatures," he explained in an 8 April statement.
The statement said that although large silver particles have been used to produce PO from propylene, "this method suffers from a low selectivity or low conversion to PO -- creating a large amount of carbon dioxide." However, Vajda claims, nanoscale clusters of silver -- consisting of three-atom clusters as well as larger clusters of 3.5 nanometers -- are highly active and selective catalysts for the production of PO.
Materials chemist Larry Curtiss and nanoscientist Jeff Greeley, both part of the research team, subsequently discovered that the "open shell electronic structure of the silver catalysts was the impetus behind the nanoclusters' selectivity," the statement said.
"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 propylene epoxidation."
"This is basically a holy grail reaction," Greeley added.
The study is a result of a collaborative team involving five Argonne divisions and collaborators from the Fritz-Haber-Institut in Berlin and from the University of Illinois in Chicago, including a collaboration between the experimental effort led by Vajda and the theoretical analysis led by Curtiss and Greeley.
PO is a commodity chemical used in the manufacture of polyurethanes and as a building block in the production of intermediate products. PO derivatives include, among others, butanediol, propylene glycol and solvents. (RD)