Two conductors for a chemical reaction

Catalysts are essential for many chemical technologies, from exhaust gas purification to the production of valuable chemicals and energy carriers. Often, small traces of additional substances are used along with catalysts to make them highly effective. These substances are referred to as “promoters”. Although it plays a crucial role in technology, it has been difficult to study.

In most cases, determining which amount of stimuli had which effects on the stimulus was a process of trial and error. However, researchers at TU Wien were able to directly observe the role of lanthanum catalysts in hydrogen oxidation. Using high-tech microscopy methods, they visualized the role of individual La atoms. Their study revealed that two surface areas of the stimulator act as pacemakers, similar to conductors in an orchestra. The promoter plays a vital role in their interaction, controlling pacemakers. The results of this study have now been published in the journal “Nature Communications.”

Watch the reaction live

“Many chemical processes use catalysts in the form of small nanoparticles,” says Professor Günter Ruprechter from the Institute of Materials Chemistry at TU Wien. While the performance of catalysts can be easily determined by analyzing the products, microscopic insights cannot be obtained by following this approach.

This has changed now. Over several years, Günter Ruprechter and his team have developed sophisticated methods that allow individual nanoparticles to be directly monitored during a chemical reaction. This allows seeing how the activity changes at different sites on these nanoparticles during the course of the reaction.

“We use rhodium nanotips that behave like nanoparticles,” says Günter Rupichter. “They can act as catalysts, for example, when hydrogen and oxygen combine to form water molecules – a reaction we study in detail.”

Oscillating between “active” and “inactive”

In recent years, the TU Wien team has already demonstrated that different regions of nanoparticle surfaces exhibit different behaviors: they oscillate between an active state and an inactive state. Sometimes, the desired chemical reaction occurs at certain locations, while other times it does not.

Using specialized microscopes, it has been shown that such different oscillations occur on each nanoparticle in parallel, and they all influence each other. Certain regions of the surface of nanoparticles, often only a few atomic diameters wide, play a more important role than others: they act as highly efficient “pacemakers,” even controlling chemical oscillations in other regions.

Promoters can now interfere with the behavior of this pacemaker, and this is exactly what the methods developed at TU Wien allowed the researchers to investigate. When rhodium is used as a catalyst, lanthanum can act as a catalyst for catalytic reactions. Individual lanthanum atoms were placed on the surface of a small rhodium nanoparticle. The same particle was examined in the presence and absence of the promoter. This approach revealed in detail the specific influence of individual lanthanum atoms on the progress of the chemical reaction.

Lanthanum changes everything

Maximilian Rabe, Johannes Zenninger and Carla Weigel performed the experiments. “The difference is huge,” says Maximilian Raab. “The lanthanum atom can bind oxygen, and this changes the dynamics of the catalytic reaction.” The small amount of lanthanum changes the coupling between different regions of the nanoparticles.

“Lanthanum can selectively inactivate some pacemakers,” explains Johannes Zenninger. “Imagine an orchestra with two conductors – we will hear very complex music. The promoter makes sure that there is only one pacemaker, which makes the situation simpler and more organized.”

In addition to the measurements, the team, with support from Alexander Genest and Yuri Suchorsky, developed a mathematical model to simulate the coupling between individual regions of the nanoparticles. This approach offers a more robust way to describe chemical catalysis than before: not just based on inputs and outputs, but in a complex model that takes into account how different regions of the catalyst switch between activity and inactivity, how they mutually influence each other, and which are controlled by promoters. .