Aluminiumorganisch stabilisierte Übergangsmetallkolloide : Synthese, Bildungsmechanismus und Aufbau von organisierten Strukturen

摘要

Subject of the dissertation is the synthesis and characterization of novel, nanoscopic transition metal colloids having reactive aluminumorganic protecting shells, and the formation of 3-D nanoparticle networks. The synthesis of aluminumorganic stabilized platinum colloids was investigated using the reaction of Pt(II)-acetylacetonate with aluminumtrimethyl. A novel di-platinum complex was identified as the key intermediate of the colloid formation. This complex decomposes in solution under formation of nanoscopic platinum particles with a mean diameter of 1.2 nm. The formation of these particles in solution was studied with Anomalous Small Angle X-ray Scattering (ASAXS). The isolated platinum colloids were characterized further with several analytic methods like Electron Microscopy (TEM) and X-ray Absorption Spectroscopy (XANES, EXAFS). The investigations showed, that the particles consist of zero-valent platinum with an aluminumorganic protecting shell containing reactive aluminum-methyl-groups. These reactive aluminum-methyl-groups are the prerequisite for the interconnection of the particles to form a 3-D nanoparticle network. For that purpose, the colloids are reacted with proton-active bifunctional "spacer-molecules". Suitable spacer molecules are diols or dicarboxylic acids which react with the aluminum-alkyl groups in the protecting shell under cleavage of methane. The structure and the electronic- and catalytic properties of the resulting Pt-nanoparticle-networks were intensively characterized. The investigations revealed, that the structure of the networks is strongly depending on the "spacer-molecule" chosen. The mean interparticle distance in the network increases with increasing length of the "spacer molecule". Variation of the "spacer molecule" also allows the pore-sizes and the specific surface areas to be tailored. Furthermore catalytic tests showed, that the Pt-nanoparticle networks are very efficient heterogeneous catalysts for the hydrogenation of alkenes.