Single atoms as catalysts

September 02, 2019

They make our cars more environmentally friendly and they are indispensable for the chemical industry: catalysts make certain chemical reactions possible - such as the conversion of CO into CO2 in car exhaust gases - that would otherwise happen very slowly or not at all. Surface physicists at the TU Wien have now achieved an important breakthrough; metal atoms can be placed on a metal oxide surface so that they show exactly the desired chemical behavior. Promising results with iridium atoms have just been published in the renowned journal Angewandte Chemie.

Smaller and smaller - all the way down to the single atom

For car exhaust gases, solid catalysts such as platinum are used. The gas comes into contact with the metal surface, where it reacts with other gas components. "Only the outermost layer of metal atoms can play a role in this process. The gas can never reach the atoms inside the metal so they are basically wasted," says Prof. Gareth Parkinson from the Institute of Applied Physics at TU Wien. It therefore makes sense to construct the catalyst not as a single large block of metal, but in the form of fine granules. This makes the number of active atoms as high as possible. Since many important catalyst materials (such as platinum, gold or palladium) are very expensive, cost is a major issue.

For years, efforts have been made to turn the catalysts into finer and finer particles. In the best case scenario, the catalyst could be made up of individual catalyst atoms, and all would be active in just the right way. This is easier said than done, however. "When metal atoms are deposited on a metal oxide surface, they usually have a very strong tendency to clump together and form nanoparticles," explained Gareth Parkinson.

Instead of attaching the active metal atoms to a surface, it is also possible to incorporate them into a molecule with cleverly selected neighboring atoms. The molecules and reactants are then dissolved into a liquid, and the chemical reactions happen there.

Both variants have advantages and disadvantages. Solid metal catalysts have a higher throughput, and can be run in continuous operation. With liquid catalysts, on the other hand, it is easier to tailor the molecules as required, but the product and the catalyst have to be separated again afterwards.

The best of both worlds

Parkinson's team at TU Wien has is working to combine the advantages of both variants: "For years we have been working on processing metal oxide surfaces in a controlled manner and imaging them under the microscope," says Gareth Parkinson. "Thanks to this experience, we are now one of a few laboratories in the world that can incorporate metal atoms into a solid surface in a well defined way."

In much the same way as liquid catalyst molecules are designed, it is becoming possible to choose the neighbouring atoms in the surface that would be the most favourable from a chemical point of view - and special surface-physics tricks make it possible to incorporate them into a solid matrix on a special iron oxide surface. This can be used, for example, to convert carbon monoxide into carbon dioxide.

Optimal control

"Single atom catalysis is a new, extremely promising field of research," says Gareth Parkinson. "There have already been exciting measurements with such catalysts, but so far it was not really known why they worked so well. Now, for the first time, we have full control over the atomic properties of the surface and can clearly prove this by means of images from the electron microscope".
-end-
This research was funded by the Austrian Science Fund START prize, awarded to Gareth Parkinson in 2015.

Contact:

Prof. Gareth Parkinson
Institute of Applied Physics
TU Wien
Wiedner Hauptstraße 8-10, 1040 Vienn
T +43-1-58801-13473
gareth.parkinson@tuwien.ac.at

Vienna University of Technology

Related Chemical Reactions Articles from Brightsurf:

Shedding light on how urban grime affects chemical reactions in cities
Many city surfaces are coated with a layer of soot, pollutants, metals, organic compounds and other molecules known as ''urban grime.'' Chemical reactions that occur in this complex milieu can affect air and water quality.

Seeing chemical reactions with music
Audible sound enables chemical coloring and the coexistence of different chemical reactions in a solution.

Nanocatalysts that remotely control chemical reactions inside living cells
POSTECH professor In Su Lee's research team develops a magnetic field-induced heating 'hollow nanoreactors'.

New NMR method enables monitoring of chemical reactions in metal containers
Scientists have developed a new method of observing chemical reactions in metal containers.

Levitating droplets allow scientists to perform 'touchless' chemical reactions
Levitation has long been a staple of magic tricks and movies.

Predicting unpredictable reactions
New research from the University of Pittsburgh's Swanson School of Engineering, in collaboration with the Laboratory of Catalysis and Catalytic Processes (Department of Energy) at Politecnico di Milano in Milan, Italy, advances the field of computational catalysis by paving the way for the simulation of realistic catalysts under reaction conditions.

First-time direct proof of chemical reactions in particulates
Researchers at the Paul Scherrer Institute PSI have developed a new method to analyse particulate matter more precisely than ever before.

Finding the source of chemical reactions
In a collaborative project with MIT and other universities, scientists at Argonne National Laboratory have experimentally detected the fleeting transition state that occurs at the origin of a chemical reaction.

Accelerating chemical reactions without direct contact with a catalyst
Northwestern University researchers demonstrate a chemical reaction produced through an intermediary created by a separate chemical reaction, findings that could impact environmental remediation and fuel production.

Visualizing chemical reactions, e.g. from H2 and CO2 to synthetic natural gas
Scientists at EPFL have designed a reactor that can use IR thermography to visualize dynamic surface reactions and correlate it with other rapid gas analysis methods to obtain a holistic understanding of the reaction in rapidly changing conditions.

Read More: Chemical Reactions News and Chemical Reactions 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.