My watch list
my.chemeurope.com  
Login  

The dance of the atoms

11-Jun-2013

TU Wien

Single Pd atoms are visible on the surface (picture 1). One of them is lifted up and mobilized (fuzzy white area in picture 2) and then moves across the surface (picture 3 and 4)

TU Wien

The Pd atom on the surface (top) is lifted up by the CO-molecule, allowing it to diffuse.

Catalysts can stop working when atoms on the surface start moving. At the Vienna University of Technology, this dance of the atoms could now be observed and explained.

Lone people standing in a ballroom don’t tend to move a lot. It’s only when they find a suitable dance partner that rapid motion sets in. Atoms on iron-oxide surfaces behave in a similar way: Only with the right molecular partner do they dance across the surface. Scientists at the Vienna University of Technology have now filmed the atoms, proving that carbon monoxide is the partner responsible for the quick motion. Their movies show that the motion leads directly to clustering – an effect that can do great harm in catalysts. The findings have now been published in the journal “Nature Materials”.

Clusters – What a waste of atoms!

“Metals such as gold or palladium are often used as catalysts to speed up certain chemical reactions”, says Professor Ulrike Diebold (Institute of Applied Physics, Vienna University of Technology). When the atoms ball together, most of them do not get into contact with the surrounding gas any more and the catalytic effect diminishes drastically. For this reason, Ulrike Diebold’s team investigates how clusters form from single atoms on a surface, and search for ways to inhibit the process.

Theories about this effect have been discussed for years, but the researchers at the Vienna University of Technology have now directly observed the clustering of the atoms. “We are using palladium atoms on an extremely clean iron-oxide surfaces in an ultra high vacuum chamber. For several hours, we take pictures of the surface with a scanning tunneling microscope”, says Gareth Parkinson (Vienna University of Technology). These pictures were then made into a movie, in which the paths of the individual atoms could be tracked.

The skyhook effect

Using this technique, the research team discovered that the rapid atomic dance on the surface is initiated by carbon monoxide molecules, which bind to individual palladium atoms. As soon as this happens, the palladium is hardly connected to the ground and can move around almost freely, as if it had been lifted out by the carbon monoxide. “This is known as the skyhook effect”, says Zbynek Novotny (Vienna University of Technology).The carbon monoxide and palladium move happily together across the surface, until they collide with other ‘dancing couples’. Then, they stick together creating a small cluster that continues to grow.

Hydroxyl against clustering?

With the new possibility of watching clustering in real-time under the microscope, the mechanisms can now be studied in detail: “We discovered that OH groups on the surface can suppress the clustering effect”, says Gareth Parkinson. If the carbon monoxide-palladium couples do not encounter each other, but instead find an OH group, they get trapped there and cannot form a cluster. A hydroxyl coating of the surface could therefore lead to a significant improvement of the stability of catalysts.

Facts, background information, dossiers
More about TU Wien
  • News

    Microprocessors based on a layer of just three atoms

    Two-dimensional materials, or 2D materials for short, are extremely versatile, although - or often more precisely because - they are made up of just one or a few layers of atoms. Graphene is the best-known 2D material. Molybdenum disulphide (a layer consisting of molybdenum and sulphur atom ... more

    Diamonds coupled using quantum physics

    Diamonds with minute flaws could play a crucial role in the future of quantum technology. For some time now, researchers at TU Wien have been studying the quantum properties of such diamonds, but only now have they succeeded in coupling the specific defects in two such diamonds with one ano ... more

    Switching oxygen on and off

    Oxygen atoms are highly reactive, yet the world does not spontaneously burn, even though everything is surrounded by this aggressive element. Why? The reason is that normal O2 molecules, are not particularly reactive. At the Vienna University of Technology, it has now been possible to selec ... more

  • Videos

    Epoxy Resin

    A flash of ultraviolet light sets off a chain reaction which hardens the whole object. more

    Noreia

    The coating machine Noreia was built at TU Wien. This time-lapse video shows the construction process. more

    Shaping Drops: Control over Stiction and Wetting

    Some surfaces are wetted by water, others are water-repellent. TU Wien (Vienna), KU Leuven and the University of Zürich have discovered a robust surface whose adhesive and wetting properties can be switched using electricity. This remarkable result is featured on the cover of Nature magazin ... more

  • Events
    Conference
    05-09 – 08-09
    2017
    Vienna, AT

    Danube Vltava Sava Polymer Meeting

    The field of polymer science continues year after year to steadily advance fueled both by academic enthusiasm and by industrial pragmatism. The numerous environmental and economic benefits of polymers make these materials popular for manufacturers, fabricators and consumers within a wide ra ... more

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE