Single atoms as a catalyst: Surprising effects ensue

January 22, 2021

Metals such as gold or platinum are often used as catalysts. In the catalytic converters of vehicles, for example, platinum nanoparticles convert poisonous carbon monoxide into non-toxic CO2. Because platinum and other catalytically active metals are expensive and rare, the nanoparticles involved have been made smaller and smaller over time.

"Single-atom" catalysts are the logical end point of this downsizing: The metal is no longer present as particles, but as individual atoms that are anchored on the surface of a cheaper support material. Individual atoms can no longer be described using the rules developed from larger pieces of metal, so the rules used to predict which metals will be good catalysts must be revamped - this has now been achieved at TU Wien. As it turns out, single atom catalysts based on much cheaper materials might be even more effective. These results have now been published in the journal Science.

Smaller is sometimes better

Only the outer atoms of the piece of metal can play a role in chemical processes - after all, the atoms inside never come into contact with the environment. In order to save material, it is therefore best to use tiny metal particles instead of large lumps, so that a greater proportion of the atoms reside at the surface. If we go to the ultimate limit and use individual atoms, every single atom is chemically active. Over the last decade the field of "single atom" catalysis has grown dramatically, achieving great success.

Wrong model, right solution

"The reasons why some precious metals are good catalysts was already researched in the 1970s," says Prof. Gareth Parkinson from the Institute for Applied Physics at TU Wien. "For example, Gerhard Ertl was awarded the Chemistry Nobel Prize in 2007 for providing atomic-scale insights into catalysis."

In a piece of metal, an electron can no longer be assigned to a specific atom; the electronic states result from the interaction of many atoms. "For individual atoms, the old models are no longer applicable" says Gareth Parkinson. "Individual atoms do not share electrons like a metal, so the electron bands, whose energy was key to explaining catalysis, simply do not exist in this case."

Gareth Parkinson and his team have therefore been intensively investigating the atomic mechanisms behind this single-atom catalysis in recent years. "In many cases the metals that we think of as good catalysts remain good catalysts in the form of individual atoms" says Gareth Parkinson. "In both cases it is the same electrons, the so-called d electrons, that are responsible for this."

Customized properties through tailored surfaces

Entirely new possibilities arise in single-atom catalysis that are not available when using ordinary metal particles: "Depending on the surface on which we place the metal atoms and which atomic bonds they form, we can change the reactivity of the atoms", explains Parkinson.

In some cases, particularly expensive metals like platinum are no longer necessarily the best choice. "Individual nickel atoms show great promise for carbon monoxide oxidation. If we understand the atomic mechanisms of single atom catalysis, we have a lot more leeway to influence the chemical processes," says Parkinson.

Eight different metals were precisely analyzed in this way at TU Wien - the results fit perfectly with the theoretical models that have now been developed in a collaboration with Prof. Cesare Franchini at the University of Vienna.

"Catalysts are very important in many areas, especially when it comes to chemical reactions that play a major role in attempts to develop a renewable energy economy," emphasizes Gareth Parkinson. "Our new approach shows that it doesn't always have to be platinum." The decisive factor is the local environment of the atoms - and if you choose it correctly, you can develop better catalysts and at the same time save resources and costs.
-end-
Contact
Prof. Gareth Parkinson
Institute for Applied Physicd
TU Wien
Wiedner Hauptstraße 8-10, 1040 Vienna
+43 1 58801 13473
gareth.parkinson@tuwien.ac.at

Vienna University of Technology

Related Atoms Articles from Brightsurf:

How to gently caress atoms
It is extremely difficult to study oxygen molecules on the metal oxide surface without altering them.

'Hot and messy' entanglement of 15 trillion atoms
In a study published in Nature Communications, ICFO, HDU and UPV researchers report the production of a giant entangled state that may help medical researchers detect extremely faint magnetic signals from the brain.

Exciting apparatus helps atoms see the light
Researchers in the Light-Matter Interactions for Quantum Technologies Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) have generated Rydberg atoms - unusually large excited atoms - near nanometer-thin optical fibers.

Manipulating atoms to make better superconductors
A new study by University of Illinois at Chicago researchers published in the journal Nature Communications shows that it is possible to manipulate individual atoms so that they begin working in a collective pattern that has the potential to become superconducting at higher temperatures.

Grabbing atoms
In a first for quantum physics, University of Otago researchers have 'held' individual atoms in place and observed previously unseen complex atomic interactions.

Chemists allow boron atoms to migrate
Organic molecules with atoms of the semi-metal boron are important building blocks for synthesis products to produce drugs and agricultural chemicals.

2D materials: arrangement of atoms measured in silicene
Silicene consists of a single layer of silicon atoms. In contrast to the ultra-flat material graphene, which is made of carbon, silicene shows surface irregularities that influence its electronic properties.

Atoms don't like jumping rope
Nanooptical traps are a promising building block for quantum technologies.

2000 atoms in two places at once
The quantum superposition principle has been tested on a scale as never before in a new study by scientists at the University of Vienna.

Single atoms as catalysts
Only the outermost layer of a catalyst can play a role in chemical reactions.

Read More: Atoms News and Atoms Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.