Periodic Reporting for period 2 - TACCAMA (Atomic-Scale Motion Picture: Taming Cluster Catalysts at the Abyss of Meta-Stability)
Periodo di rendicontazione: 2021-07-01 al 2022-12-31
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.
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.
In the first funding period, we have installed a new APSTM in our lab at the Technical University of Munich, which we have purchased from SPECS. The instrument is now in routine operation and used for measurements of metal particles on oxide supports under realistic reaction conditions.
The main achievements so far are centered predominantly around ultra-high-vacuum precursor studies, where we demonstrated several key points for the future progression of the project. First, we have shown that the combination of pulsed reactivity measurements and microscopy is highly effective in disentangling reaction mechanisms on well-defined model catalysts. Second, we have proven that video-rate STM and atom tracking are ideally suited to following diffusion processes directly, such as the motion of small metal particles or structural changes in the oxide support. Third, we have successfully transported size-selected metal clusters deposited in Munich to a synchrotron facility for measurements on these highly defined model catalysts. And fourth, we have successfully performed first proof-of-concept STM experiments under realistic reaction conditions.
The main achievements so far are centered predominantly around ultra-high-vacuum precursor studies, where we demonstrated several key points for the future progression of the project. First, we have shown that the combination of pulsed reactivity measurements and microscopy is highly effective in disentangling reaction mechanisms on well-defined model catalysts. Second, we have proven that video-rate STM and atom tracking are ideally suited to following diffusion processes directly, such as the motion of small metal particles or structural changes in the oxide support. Third, we have successfully transported size-selected metal clusters deposited in Munich to a synchrotron facility for measurements on these highly defined model catalysts. And fourth, we have successfully performed first proof-of-concept STM experiments under realistic reaction conditions.
Project TACCAMA is - to the best of our knowledge - the first to combine realistic reaction pressures and temperatures with atomically precise control over catalyst particles and with real time microscopy on individual particles. The novelty of the project lies in correlating directly the structural dynamics of a model catalyst (e.g. particle diffusion and sintering into larger ones, support restructuring, and so on) with its catalytic activity.
We expect this project in the second funding period to provide us with fundamental insights into the parameters controlling model catalyst stability and reactivity. By identifying the most active particle sizes, we anticipate the production of more material efficient catalysts will be made possible. Furthermore, an atomic-scale understanding of mechanistic details of such catalytic processes is key to developing new, sustainable and energy efficient materials for industrial chemistry.
We expect this project in the second funding period to provide us with fundamental insights into the parameters controlling model catalyst stability and reactivity. By identifying the most active particle sizes, we anticipate the production of more material efficient catalysts will be made possible. Furthermore, an atomic-scale understanding of mechanistic details of such catalytic processes is key to developing new, sustainable and energy efficient materials for industrial chemistry.