Stabilization of nanoscale noble metal islands on oxide supports by manipulation of the surface texture

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Catalytic activity of metal nanoparticles is tied to their size via the specific surface area but also intrinsically, in the case of structure sensitive reactions. To maintain a high dispersion of the catalytically active phase in a reactor metals are therefore commonly used in supported form, where nanoparticles are deposited onto the surfaces of oxide carrier materials. However, under elevated process temperatures sintering and particle growth are commonly observed. The goal of the proposed project is the immobilization of metal islands on oxides to prevent sintering by texturing the support surface. Support material will be synthesized in the form of particles of SiO2, TiO2 and Al2O3 via Chemical Vapor Synthesis and flame spray pyrolysis which will be textured in various ways. After establishing a library of surface textures in the first phase of the project, the materials will be tested for their ability to stabilize metallic particles. For this Pt-islands will be deposited on selected oxide structures by chemical vapor deposition. In subsequent tempering experiments the mobility of the islands and the evolution of their size will be monitored and kinetic parameters of the sintering process will be extracted. Over the duration of the project small angle x-ray scattering (SAXS) will play an important role as an analytic method allowing the quantification of surface texture by determining the surface fractal dimension. In addition, the surface chemistry of the support particles will be examined in detail using x-ray photoelectron spectroscopy (XPS) to enable the extraction of the purely physical structural effects from the sintering kinetics determined.