Bildung und Nutzung von definierten Reaktionsräumen

Sommersemester 2002

13.05.2002 Prof. Dr. Markus Albrecht, RWTH Aachen
  Metallkoordination als Hilfsmittel zur Stabilisierung molekularer und supramolekularer Strukturen
  Molekulare Erkennung und Selbstorganisation spielen eine wichtige Rolle bei der Bildung und Funktion biologischer Systeme. Nicht-kovalente Wechselwirkungen ermöglichen dabei die reversible Bildung von Bindungen und den selektiven Aufbau großer Strukturen mit definierten Funktionen.
Ähnlich lassen sich auch künstliche Strukturen erhalten, die neue Eigenschaften aufweisen, oder dabei helfen, fundamentale Prinzipien und Mechanismen nicht-kovalent verknüpfter Systeme zu verstehen. Die Selbstorganisation Helicat-artiger Metallkomplexe ist dabei ein wichtiger Aspekt Metallosupramolekularer Chemie. Das Design geeigneter Liganden, die faszinierenden Strukturen der gebildeten Koordinationsverbindungen und die Mechanismen der Metall-gesteuerten Selbstorganisation sind der Schwerpunkt unserer Arbeiten. Zusätzlich beschäftigen wir uns mit der Nutzung von Metallkoordination zur Fixierung von Peptidmikrostrukturen, um deren biologische Aktivität beeinflussen zu können.
27.05.2002

Dr. Libuda, Fritz-Haber-Institut, MPG, Berlin

  Molekularstrahlexperimente an Modellkatalysatoren
  Many heterogeneous catalysts are based on nanometer-sized active particles, dispersed on an inert support material. It is assumed that the unique reactivities of such surfaces arise from the simultaneous presence of different active sites, the specific properties of nanometer-sized particles or the influence of the support. On a molecular level, however, knowledge on the reaction kinetics on such systems is scarce.
In order to approach a microscopic understanding of the reaction kinetics on complex surfaces, we combine molecular beam techniques, in situ spectrosopy and a supported model catalyst approach.
The model systems are prepared under ultrahigh vacuum conditions and have been characterized with respect to their geometric and electronic structure, previously. In order to probe the kinetics of catalytic reactions on these systems, we have developed a molecular beam instrument, which allows to cross up to three beams on the sample surface. The simultaneous detection of reaction products and surface species is established by a combination of angle- and time-resolved gas phase detection and in situ time-resolved IR reflection absorption spectroscopy (TR-IRAS).
A variety of experiments are reviewed, illustrating the experimental possibilities of the molecular beam approach. As a model surface, we focus on alumina supported palladium particles of different structure and size. We cover the adsorption and desorption kinetics of small molecules and the kinetics of surface reactions of different complexity. The reaction kinetics is probed via systematic steady state measurements, transient experiments, time-resolved in-situ IR spectroscopy and measurements of the angular distribution of products.
As a first and rather simple model reaction, we consider the CO oxidation, which has been thoroughly investigated on a variety of single crystal surfaces. For the supported model catalysts, it is shown, how structure and size dependencies can be identified by performing systematic kinetic measurements. These effects can be linked to the inherent heterogeneity of the model surfaces via microkinetic mean-field and Monte Carlo simulations. Kinetic effects on the model catalyst surfaces can be understood by explicitly accounting for their inherent complexity. As a first example of a more complex reaction system we consider the decomposition and oxidation of methanol. Different mechanistic aspects are investigated such as reverse spillover from the support to the Pd particles and the formation of intermediates. The kinetics of CO and CO2 formation is probed by multiple beam experiments involving conventional gas phase detection and isotope exchange / TR-IRAS. The selectivity with respect to two competing decomposition channels, dehydrogenation to CO and C-O bond scission, is studied combining different types of quantitative beam experiments and in-situ spectroscopy. It is shown that the two reactions preferentially occur at different active sites on the nanoparticles.
17.06.2002 Prof. Dr. Jeffery Davis, University of Maryland, USA
  Self-Assembled Ionophores: Toward Control of Structure, Stereochemistry and Properties
24.06.2002 Dr. Thomas Straßner, TU München
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Die Vorträge finden statt: montags, 17 Uhr c.t., Universität Oldenburg, W3-1-156, Carl-von-Ossietzky-Str. 9-11.