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Synthesis

Single Atoms Mediate Reaction

Catalysis: Isolated platinum atoms remain stable and active in oxidations

by Mitch Jacoby
August 1, 2011 | APPEARED IN VOLUME 89, ISSUE 31

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Credit: Jun Li/Tsinghau U
Single platinum atoms (yellow balls and three bright spots in TEM image) on iron oxide (purple and gray) mediate conversion of CO to CO2.
08931-notw6-JunLi3cxd.jpg
Credit: Jun Li/Tsinghau U
Single platinum atoms (yellow balls and three bright spots in TEM image) on iron oxide (purple and gray) mediate conversion of CO to CO2.

A wet-chemistry method can be used to prepare catalysts featuring single isolated precious-metal atoms supported on a metal oxide surface, according to a research team based in China and the U.S. (Nat. Chem., DOI: 10.1038/nchem.1095). The work may lead to low-cost industrial catalysts and addresses questions in fundamental catalytic science.

Supported catalysts consisting of particles of platinum and other precious metals anchored on oxides are widely used in automotive emissions cleanup and many industrial catalytic processes. Because only the metal atoms at the particle surfaces catalyze reactions, manufacturers aim to make these particles as tiny as possible to maximize metal use. But making uniform subnanometer-sized particles remains challenging. And the tiny particles’ tendency to diffuse and agglomerate deactivates catalysts.

By tuning the temperature, pH, and other parameters in a coprecipitation process, the China-U.S. team has come up with a synthesis that sidesteps those problems. Using atomic-resolution microscopy and other analytical methods, Botao Qiao and Tao Zhang of China’s Dalian Institute of Chemical Physics; Jun Li of Tsinghua University, in Beijing; Jingyue Liu of the University of Missouri, St. Louis; and coworkers have determined that their procedure yields nanocrystallites of iron oxide with isolated platinum atoms dispersed across the surface.

The group compared the single-atom catalyst with other platinum catalysts and with a high-performance gold reference catalyst in CO oxidation reactions. One set of tests evaluated the catalysts’ ability to oxidize CO in the presence of an abundance of hydrogen. The reaction rids hydrogen of low levels of CO, a common contaminant that poisons fuel-cell catalysts. In all cases the researchers found that the single-atom catalyst remains stable under typical reaction conditions and is at least two to three times more active than the other catalysts.

“This is very exciting and timely work,” says Charles H. F. Peden of Pacific Northwest National Laboratory. The catalysis community has been considering whether a single atom can serve as the active site in heterogeneous catalysts, he notes. “This study answers the question with a resounding yes,” he adds.

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