Speaker
Description
Transition metals such as copper (Cu) play a central role in heterogeneous catalysis and are widely used in industrial processes such as methanol synthesis. Stabilizing small Cu clusters or even isolated atoms on oxide supports is a common strategy to enhance catalytic performance. While magnesium oxide (MgO) is one of the best-characterized oxide materials, featuring well-defined, nonpolar surfaces and high stability, it is generally considered catalytically inert. Nevertheless, metal–support interactions can significantly alter the structural and electronic properties of supported metals, making MgO a suitable model system for fundamental studies.
This presentation covers thin-film and oxidation effects on Cu atoms and small clusters supported on MgO films grown on a silver single crystal Ag(100) under ultra-high vacuum conditions. MgO and Cu were deposited by e-beam evaporation. The system was characterized using Reflection-Absorption Infrared Spectroscopy (RAIRS), X-ray Photoelectron Spectroscopy (XPS) and complementary Scanning Tunneling Microscopy (STM). RAIRS provides insight into clustering behavior and charge state, while XPS was used to determine the oxidation state of Cu. STM measurements offer additional structural information on cluster morphology.
The experiments with different Cu coverage and MgO films of various thicknesses demonstrate a complex nucleation behavior of Cu, ranging from single atoms and small clusters to three-dimensional particles. Additionally, differences in the oxidation and reduction behavior have been observed for small and large Cu particles. Interestingly, the oxidation of Cu on the surface of an ultrathin MgO film can also be achieved by the thermally induced diffusion of interfacial oxygen atoms, which form during the preparation of high workfunction MgO at the Ag/MgO interface. These results provide a comprehensive understanding of the metal-support interactions for Cu/MgO model catalysts.