Catalysts are substances that increase the rate of a chemical reaction. The EU-funded project TACCAMA aims to study the correlation between the structural dynamics and activity of model catalysts at the atomic scale. To do so, we use a scanning tunnelling microscope (STM) with high-temporal and spatial resolution directly in reactive gas mixtures. Simply put, we build up a model of a catalyst with atomic precision: single crystalline thin film or bulk oxides serve as supports onto which atomically defined particles are deposited as catalysts. These models are then investigated microscopically in a small reactor where we can control the temperature, gas composition and pressure while at the same time recording images and movies. This approach allows us to investigate how the structures of catalyst particles and substrates change under reaction conditions, i.e. elevated temperatures and ambient pressures.
In addition to the microscopic investigations, we also perform X-ray photoelectron spectroscopy (XPS) under identical conditions (same temperature, same gas composition and same pressure) so that we can correlate chemical with structural information. Finally, we use a pulsed reactivity setup to observe the reaction as it proceeds, i.e. monitor systematically the generation of different product molecules under the various conditions.
By using small clusters with a precisely defined number of atoms, we can investigate how highly reactive particle structures appear and disappear, how this process can be controlled, and how it influences the catalyst function. Essentially, in the regime of these very small, sub-nanometre particles, even the addition of a single atom can lead to a significant change in the stability and reactivity of the resulting catalyst. We thus anticipate this knowledge will lead to the development of more cost-effective alternatives to the precious metal catalysts commonly used today, e.g. by using only the particles with the optimal size.
