Dynamics of ceria-supported cluster formation and redispersion – from fundamentals to catalytic control

• Applicants: Privatdozent Dr. Friedrich Esch; Professor Dr. Ulrich Heiz
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569736450

This project investigates the dynamics of cluster diffusion, formation and redispersion on ceria supports with sophisticated fast scanning tunneling microscopy (STM) tools - fast movies and cluster tracking. As a catalytically relevant support, we choose ceria, a reducible oxide that shows intricately entangled redox-coupled electron and oxygen buffering capacities, a low tendency to encapsulate supported particles, but the possibility to reversibly take up charged atomic species at steps. While these properties and the catalytic activity have been well studied by integral and local methods to formulate the fundamental concepts, the dynamics of these processes at the atomic scale largely remain elusive. This purpose requires measurements that combine high spatial and temporal resolution (down to the ms) with precise access to various support morphologies (vacancy and step distribution) and atomically precise control of the size of deposited clusters, independent of their coverage. Only in this way can specific sizes of transient, particularly stable or diffusive species be identified and correlated to specific properties and support morphologies. We investigate the influence of the local environment on the diffusion paths of clusters, the fluxionality upon diffusion, the involved activation energies, and adsorbate- and interface-redox-induced mobility. We tackle five research objectives in a hierarchically increasing complexity, namely: (i) the dynamics of the ceria (111) support, (ii) the mobility of Au adatoms, (iii) the mobility of bare Pt clusters, (iv) the cyclic transformation between Pt clusters and redispersed Pt2+ at steps, and (v) the dynamics of supported Pt clusters in reactive gas ambients. These studies shed, for the first time, light on the dynamic intermediates in redox-induced cyclic formation and redispersion of active particles in catalysis, on concomitant spillover phenomena and reversible oxygen storage in reactive gas environments, as well as on the modulation of the oxidation state of diffusing atoms and clusters. The unique experimental infrastructure required is currently only available at our TUM laboratory. We anticipate that the obtained insights will also pertain to describing the dynamics of structurally more complex powder cluster catalysts in action regarding the dynamic formation and redispersion of clusters and their intimate link to catalytic activity. They will also steer future theoretical modeling by significantly reducing the parameter space to be spanned, with an impact beyond the specific case of ceria supports.

• DFG Programme: Research Grants