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Manufacturing Bits: April 30

Single-atom catalysts; nerve agents; plasmons.

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Single-atom catalysts
A group of researchers have captured the behavior of a single-atom catalyst, a move that could one day help design more efficient catalysts in systems.

A catalyst is a substance that increases the rate of a chemical reaction. In vehicles, for example, platinum is used as a catalyst, which speeds up chemical reactions and cleans exhaust gases. Besides platinum, the industry is exploring the use of other and lower-cost materials for catalysts, such as iron, copper and aluminum.

The University of California at Santa Barbara and the University of California at Irvine have been able to control one common type of catalyst, platinum, on a surface. Researchers also demonstrated how changing the position of atoms can create different reactions. The experiments took place at the Department of Energy’s SLAC National Accelerator Laboratory.

More specifically, researchers looked at platinum atoms, which were attached to separate nanoparticles based on titanium dioxide. In the lab, this structure was developed. Then, the nanoparticles were exposed to chemical treatments using X-rays at the Stanford Synchrotron Radiation Lightsource (SSRL). The SSRL is a high-brightness third-generation storage ring, which allows researchers to study materials at the atomic and molecular level.

Using transmission electron microscopy (TEM), researchers observed the attachments and positions of the platinum atoms. Then, they measured the reactions. The positions of the atoms varied depending on the chemical treatment. At times, the atoms were embedded in the surface. At other times, the atoms were standing on the surface.

The change effects the catalytic reaction. This involves the conversion of carbon monoxide to carbon dioxide. “We believe this is the first time the reactivity of a metallic single-atom catalyst has been traced to a specific way of attaching it to a particular supporting structure. This study is also unique in systematically controlling that attachment,” said Simon Bare, a distinguished staff scientist at SLAC’s SSRL. “This is an important scientific breakthrough, and understanding on a fundamental level how the structure relates to the reactivity will ultimately allow us to design catalysts to be much more efficient.”

A new study precisely controlled the attachment of platinum atoms (white balls) to a titanium dioxide surface (latticework of red and blue balls). (Credit: Greg Stewart/ SLAC National Accelerator Laboratory)

Nerve agents
The U.S. Department of Energy’s (DOE) Brookhaven National Laboratory are exploring catalysts that decompose and eliminate the harmful effects of nerve agents.

Specifically, researchers have focused on a deadly nerve agent called sarin. The goal is to develop smart air filters and catalysts that destroy sarin before it reaches soldiers on the battlefield.

For years, scientists have been testing various methods of reducing the effects of chemical warfare agents (CWAs). Filtration is one method. This involves using an absorbent material like a sponge. This in turn prevents the chemicals from spreading, but filtration is limited.

In previous studies, researchers have demonstrated a material called polyoxometalate (POMs), which can decompose nerve agents. Researchers from Brookhaven have found a new material, which involves zirconium atoms connected to two POM molecules.

The technology is promising, but it’s still in the R&D phase. Researchers are in the process of designing catalysts with isolated zirconium and other porous materials. “Our work is part of an ongoing, multiagency effort to protect soldiers and civilians from chemical warfare agents,” said Anatoly Frenkel, a physicist with a joint appointment at Brookhaven Lab and Stony Brook University. “The research requires us to understand molecular interactions on a very small scale, and to develop special characterization methods that are capable of observing those interactions. It is a very complex set of problems that also has a very immediate societal impact.

“To identify why a catalyst works, you have to find its active site,” Frenkel said. “We hypothesized that the isolated zirconium atoms were the active sites for this catalyst. To test that theory, we analyzed the material not just by one method, but by many characterization techniques—a multimodal approach that enabled us to isolate the active molecules from ones that are not changing during the reaction.”

Plasmons
The National Institute of Standards and Technology (NIST) is exploring a new class of catalysts that work at room temperature.

Typically, catalysts enable chemical reactions at high heat. NIST’s catalysts use sunlight or another light source to create reactions with localized surface plasmons (LSPs). A “plasmon is a quantum of plasma oscillation,” according to Wikipedia.

In the case of LSPs, they involve oscillations of groups of electrons. This includes metal nanoparticles, such as gold, silver and aluminum. “Scientists had previously shown that molecular hydrogen can be split into its individual atoms by the energy generated by the LSP oscillations,” according to NIST. “The NIST team has now discovered a second LSP-mediated reaction that proceeds at room temperature.”



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