Photoelectron diffraction of Rh nanoparticles growth on Fe3O4/Pd(111) ultra thin film

Full text: Heterogeneous catalysis is a highly complex process. Usually, a catalyst is formed by transition metal nanoparticles (for example, Pd, Pt, Rh, Ni, Au) supported by an oxide such as alumina, silica, titania among others [1-4]. The performance of the catalyst in terms of macroscopic chemical parameters such as the temperature for reaction activation, selectivity and efficiency can be strongly influenced by different characteristics of the catalyst at the atomic level, for instance, its electronic and atomic structure, particle size and shape, crystallographic structure [5-6] and support material effects[1]. Metal-oxide-based catalysts are used for many important synthesis reactions in the chemical industry, such as selective oxidation, dehydrogenation, isomerization and other chemical processes [7]. Rhodium nanoparticles have been used, for example, in the studies of propionaldehyde decomposition under ultra-high vacuum (UHV) conditions. The aim of this work is to prepare rhodium nanoparticles on magnetite (Fe3O4) (111) growth on Pd(111). The rhodium clusters and iron oxide ultra-thin films (thickness <10ML) were prepared in UHV conditions by Molecular Beam Epitaxy (MBE) and keeping the substrate at 450 deg C. The system was characterized by X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and photoelectron diffraction (PED) performed at the SGM beam line at the Brazilian Synchrotron Light Source (LNLS). Our results shows the formation of small Rh an island with the same atomic structure of fcc Rh at bulk, and thickness lower then 5MLs. The islands cover approximately 15% of the iron surface. These findings were determined mainly with the PED experiments supported by a comprehensive simulation approach based on multiple scattering calculations. References: [1] J. Libuda, H.-J. Freund, Surf. Sci. Rep. 57, 157 (2005). [2] C. R. Henry, Surf. Sci. Rep. 31, 231 (1998). [3] N. Nilius, A. Corper, G. Bozdech, N. Ernst , H.-J. Freund, Prog. Surf. Sci. 67, 99 (2001). [4] C. T. Campbell, Surf. Sci. Rep. 27, 1 (1997). [5] M. Frank, S. Andersson, J. Libuda, S. Stempel, A. Sandell, B. Brena, A. Giertz, P. A. Bruhwiler, M. Baumer, N. Martensson, H.-J. Freund, Chem. Phys. Lett. 279 92 (1997). [6] S. Andersson, M. Frank, A. Sandell, A. Giertz, B. Brena, P. A. Bruhwiler, N. Martensson, J. Libuda, M. Baumer, H.-J. Freund, J. Chem. Phys. 108 2967 (1998). [7] G. Ertl, H. Knozinger, J. Weitkamp, Handbook of Heterogeneous Catalysis, Wiley-VCH, Weinheim, 1997. (author)