Open possibilities of nanoscale islands for the application of single atom catalysts

A new method for anchoring single atoms of platinum-group metals to nanometer-sized islands enables efficient use of these expensive metals as catalysts for a wide variety of applications.

Report in the newspaper Natureresearchers, including Professor Bruce Gates, from the Department of Chemical Engineering at the University of California, Davis, have shown that platinum atoms can be confined to small islands of cerium oxide within a porous material to catalyze reactions without sticking to each other, which has been a major pitfall for their use. The study was led by Jingyue Liu, a professor at Arizona State University, Gates, and Yong Wang, a professor at Washington State University.

“Stabilising precious metals to allow every atom to be a catalyst is a holy grail in the field of catalysis,” said Wang, who is also a researcher at Pacific Northwest National Laboratory. “Not only are we using the least amount of platinum group metals, but we are also making each atom much more reactive.”

Catalysts, which speed up chemical reactions, are essential to technologies used in the manufacture of chemicals and fuels and for cleaning up pollutants, including exhaust from cars, trucks and fossil fuel power plants. Many catalysts contain precious metals such as platinum, rhodium and palladium which are extremely expensive.

In the early 1990s, researchers began investigating how to isolate metal atoms as catalysts, but they had been unable to stabilize them at the high temperatures required for catalytic converters and other practical applications. Once metal atoms are exposed to the conditions required for reactions, they tend to clump together.

Scatter metal atoms on islands

The research team solved the problem by dispersing the metal atoms into nanoscale islands of cerium oxide. The many islands are based on a commercial support of silicon dioxide which is widely used in many common catalytic reactions, but the metal atoms are excluded from the support. With its extremely high surface area, silicon dioxide is able to anchor a very large number of islands containing the metal atoms in a small volume. The cerium oxide sticks like a glue to silicon dioxide and holds the individual metal atoms tightly together so they don’t drift apart to find each other, clump together and become ineffective.

The researchers found that the metal atoms confined within the island were stable in catalyzing reactions under both oxidative and reductive conditions. Oxidation, in which oxygen is added to a substance, is used in emissions control technology to remove harmful carbon monoxide and unburned hydrocarbons. Reduction, in which hydrogen is present and reacts with other molecules, is used for many industrial applications, including to produce fuels, fertilizers and medicines.

“The atomic precision in the fabrication of the new catalysts can open avenues for designing catalysts with unprecedented flexibility in placing a targeted number of atoms on each island,” Gates said. “This allows us to study reactivity and identify the most reactive species – to find out which structures and configurations are the most efficient.”

The researchers hope to further study the approach for a wide range of catalytic applications.

“This work gives the scientific community a new tool in the toolbox to understand the catalytic site requirements for specific reactions of interest and to develop new highly active and stable catalysts,” Liu said. “This creates huge opportunities for catalytic technology and brings atomic dispersion metal catalysts one step closer to practical applications.”

The work was funded by the Chemistry Division of the National Science Foundation and the U.S. Department of Energy’s Basic Energy Sciences Division of Chemical Sciences, Geosciences, and Biosciences under the Catalysis Science Program.