Observing while it happens: Operando Electron Microscopy in Catalysis Research

Our aim is to understand processes that lead to the emergence of catalytic function though direct observation using a combination of operando scanning and transmission electron microscopy.
Starting with simple model catalysts, such as polycrystalline metal foils, we observe the propagation of chemical waves and reveal how catalytic activity depends on grain orientation, coupling mechanisms and reaction conditions. In the case of redox-reactions on non-noble metals, we find that the active catalyst is operating near a phase-boundary where metallic and oxidized phases co-exist. Real-time imaging reveals fascinating oscillatory redox dynamics that increase in complexity with increasing chemical potential of the gas-phase. When moving from simple model catalysts to industrially relevant metal nanoparticles supported on reducible oxide carriers, we apply in-situ transmission electron microscopy to study effects related to a strong metal-support interaction (SMSI) under reactive conditions. Using the archetypical titania supported platinum nanoparticles as a reference system, and hydrogen oxidation as model redox reaction, it will be shown that the well-described encapsulated state of platinum particles is lost as soon as the system is exposed to a redox-active environment. Structural incoherence at the platinum-titania interface lowers the barrier for redox processes, which give rise to dynamic reconstructions and particle migration. The particle orientation on the support determines the structure of the interface and the resulting particle dynamics, migration, and sintering behaviour. The aim of the presentation is to demonstrate that active catalysts are dynamically adapting to the reaction environment and that catalytic function is related to the catalysts ability to participate in the reaction through reversible changes in its structure and/or (local) composition.

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Marc Willinger studied physics at the Vienna University of Technology and received his PhD from the Technical University of Berlin for work carried out at the Fritz Haber Institute of the Max Planck Society in Berlin. After a post-doc at the University of Aveiro in Portugal, he returned to the Fritz Haber Institute as a group leader and started to develop and implement tools for multiscale operando electron microscopy. In 2018, he accepted a position as technical director at the Scientific Centre for Optical and Electron Microscopy (ScopeM) at ETH Zurich. Since 2022 he is full professor at the Technical University of Munich. Marc Willinger is interested in the relationship between structure/composition and the resulting physical/chemical properties of materials, in particular the emergence of synergistic effects and non-linear dynamics in non-equilibrium material systems.