Dynamics of cluster catalysts under reaction conditions

Catalysts are substances that make it easier for a particular chemical reaction to happen, without being themselves consumed in the reaction. This may mean that some industrial processes require lower temperatures, and therefore less energy. In other cases, some chemicals cannot be obtained at all without using a catalyst. Designing new catalysts holds enormous potential to reduce the worlds energy consumption and enable new technological developments. However, the problem is that we often do not understand well enough how catalysts actually work to make progress in improving them. We now know that a catalyst typically looks very different from its default state while it is being used in a reaction: It may constantly change its shape and chemical composition, and this is an important part of its function. Understanding this active state is crucial in order to design new and better catalysts. In my project, I will investigate a special class of catalysts consisting of small clusters of just a few metal atoms, which sit on some cheap material. Interestingly, it turns out that this support material also plays a big role in the activity of the catalyst, and part of the project is to investigate this interaction. Because real catalysts are so complex and hard to understand, the plan is to use model systems: Starting from a highly ordered support (a single crystal), it is possible to know exactly where every single atom is. I will then use a size-selective cluster source, which again allows obtaining extremely high control over what exactly is put onto this surface for example, lots of clusters that all consist of exactly seven platinum atoms. Creating these very well-defined systems will make it easier to later interpret what happens during a reaction. To look at the clusters at the conditions that interest us, I will use a special type of scanning tunnelling microscope, which allows looking at single atoms while adding some low pressure of a reaction gas mixture and to heat up the sample. These conditions are still more mild than what is typical for a real catalyst, but are enough to already see some dynamics. With these tools, I will then first determine what types of gas mixtures and temperatures are most interesting to explore. Once this becomes clear, I can take the same samples and expose them to much higher pressures in a microreactor, where it is also possible to detect reaction products. Going back and forth between microscopy, the reactor, and additional spectroscopic experiments, I will be able to explore what exactly happens to the clusters while they catalyse a reaction and how, exactly, the catalysis works.