Platinum is an important catalyst. But until now, no one knew exactly how platinum atoms behaved during catalysis.
What happens if a cat climbs a sunflower? The sunflower is unstable, will bend quickly, and the cat will fall to the ground. However, if the cat just needs a quick push to catch the bird from there, then sunflowers can act as a “metastable intermediate step”. It is basically a mechanism by which the individual atoms of the catalyst capture the molecules to change them chemically.
Several years ago, the surface physics group of the Vienna University of Technology discovered that a “single atom” platinum catalyst could oxidize carbon monoxide at temperatures that, according to their theoretical model, should not be possible. Now, with the help of atomic-scale microscopy images and complex computer simulations, they have been able to show that both the catalyst itself and the material to which it is anchored assume an energy-unfavorable “metastable” state for a short time to allow the reaction. happens in a special way. The results have been published in the journal Science Advances.
Single Atom as Catalyst
Research group Prof. Gareth Parkinson at the Institute of Applied Physics in Technical University of Vienna is investigating the smallest possible catalyst: Individual platinum atoms are placed on the surface of the iron oxide. They then come into contact with carbon monoxide gas and turn into carbon dioxide, as happens in modern car exhaust.
“This process is technically very important, but what actually happens when the size of the catalyst is reduced to the single atomic limit was not clear until now,” said Gareth Parkinson. “In our research group, we study such processes in several ways: on the one hand, we use a scanning tunneling microscope to produce very high-resolution images where you can study the movement of individual atoms. And on the other hand, we analyze the reaction process by spectroscopy. and computer simulation.”
Whether platinum atoms are active as catalysts depends on temperature. In the experiment, the catalyst is heated slowly and evenly until it reaches a critical temperature, and carbon monoxide is converted into carbon dioxide. That threshold is around 550 Kelvin. “However, this does not match our original computer simulation,” said Matthew Meier, the first author of the current publication. “According to density function theory, which is usually used for such calculations, the process can only take place at 800 Kelvin. So we know: Something important has been overlooked here until now.”
Metastable condition: short -lived, but important
Over several years, the team accumulated extensive experience with the same ingredient in other reactions, and as a result, a new picture emerged step by step. “With density function theory, you usually calculate the state of the system that has the lowest energy,” says Matthias Meier. “That makes sense, because that’s the state the system assumes most often. But in our case, there’s a second state that plays a central role: The so-called metastable state.”
Both platinum atoms and iron oxide surfaces can switch between different quantum physical states. The ground state, with the lowest energy, is stable. When a system changes to a metastable state, it inevitably returns to its ground state after a while — like a cat trying to reach the top with an unstable climbing pole. But in the catalytic conversion of carbon monoxide, it’s enough for the system to be in a metastable state for a very short time: While a wobbly climbing state might be enough for a cat to catch a bird with its claws, the catalyst can convert carbon monoxide into a metastable state.
When carbon monoxide was first introduced, two platinum atoms bonded together to make a dimer. When the temperature is high enough, the dimer can move to a disadvantageous position where the surface oxygen atoms are less weakly bonded. In its metastable state, the iron oxide changes its atomic structure at exactly this point, releasing the oxygen atoms that the carbon oxides need to form carbon dioxide, which immediately flies away — completing the catalysis process. “If we include these previously unaccounted short-term states in our computer simulations, we get exactly the same results that were also measured in the experiment,” said Matthias Meier.
“Our results show that in surface physics you often need a lot of experience,” says Gareth Parkinson. “If we don’t study very different chemical processes for many years, we may never be able to solve this puzzle.” Recently, artificial intelligence has also been used with great success to analyze quantum chemical processes — but in this case, Parkinson believes, it probably won’t work. To come up with creative solutions beyond what was previously thought possible, you may need people.
(Materials provided by Vienna University of Technology)
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Solo, Friday, April 29, 2022. 2:50 pm
‘warm greetings full of love’
Suko Waspodo
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Ordinary Man
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