Metal clusters fewer than 100 atoms in size are partway between molecular and bulk systems and thus exhibit special physical and chemical properties. Size-selected clusters [1] provide the unique possibility to investigate the catalytic activity of small particles just one atom apart in size with both local and averaging techniques. We investigate such metal clusters on well-defined supports with the aim to extend our fundamental understanding of the influence of cluster size, structure and chemical environment on catalyst stability and activity. Using scanning tunneling microscopy (STM), we can distinguish between different structural isomers of clusters. By accelerating the instrument to video frame rates [2], we even observed reversible isomer switching. Furthermore, we compared the diffusion of a Pd atom and cluster in an h-BN pore on Rh(111) [3]. In contrast to the mobile Pd clusters on h-BN, Pt clusters on Fe3O4(001) are more sinter-resistant and instead appear to sink into the surface with increasing temperature. We find that the Fe3O4(001) support [4] is a highly dynamic system where Fe ions and adsorbates alike are mobile just above room temperature already. Another highly sinter-resistant system is that of Pt clusters on the native oxide of Si wafers, allowing us to transport them through air. In ambient pressure XPS investigations at a synchrotron, we observe a systematic difference between p- and n-doped Si wafers which is reflected in their interaction with oxygen and catalytic activity.

Monitoring the dynamics and chemical state of size-selected cluster catalysts

2019 Fall National Meeting

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