Dr. Stefan Vajda is a Senior Chemist at the Materials Science Division of the Argonne National Laboratory. His received his Master Degree in Physical Chemistry and PhD Degree in Chemistry at the Charles University Prague, Czechoslovakia; and Habitation Degree in Physics at the Free University Berlin, Germany. His current research interest is nanocatalysis by size-selected subnanometer clusters and nanoparticles, including the in situ characterization of the cluster based catalysts with X-ray techniques. Ongoing work focuses on dehydrogenation and hydrogenation reactions, CO2 conversion, as well as the use of clusters in electrochemical processes such as water splitting, CO2 conversion and Li-oxygen chemistry. Dr. Vajda has about 100 peer reviewed publications.
Small clusters consisting of a well-defined number of atoms can be regarded as models of individual catalytic active sites, and changes in their size and composition by a single atom can lead to a considerable change in their activity and selectivity support. The catalysts were produced by the deposition of size-selected subnanometer clusters of single size / composition or narrow clusters size distributions from a cluster beam on oxide and carbon based supports for subsequent tests and characterization.
The first part of the lecture we will focus on the effect of cluster size, composition and support on the properties and catalytic performance of cobalt-based catalysts in the conversion of carbon monoxide with hydrogen, followed by dehydrogenation of cyclohexene on size-selected cobalt clusters. In both cases we will discuss the insights gained from in situ X-ray scattering and absorption experiments which can, under realistic reaction conditions, deliver information about the oxidation state of the clusters, as well as about the evolution of the catalysts under various reaction conditions, such as dynamic assembly and disassembly of clusters. In the second part of the presentation, we will highlight the size-dependent performance of silver and palladium clusters in Li-air batteries and water splitting, respectively.