Controlling Steric and Chemical Influences.
Catalyzed reaction pathways lead to higher rates by either increasing the number of transition states of by reducing the difference in the standard free energies of ground and transition state. Conventionally, we seek new catalysts by tailoring the strength of interactions with reactants, intermediates and products along a reaction pathway. The relations between these interactions and specific material properties have been well described by scaling and volcano type relationships. Using reactions of alkanes and polar molecules, the lecture will show strategies, how to selectively stabilize transition states and reduce transition state energies.
The chemical and thermodynamic consequences of such approaches and the extent by which rate enhancements can be achieved will be discussed. Three elements will be compared, the role of the active center, the impact of transition state stabilization on reaction rates and novel approaches to control the standard chemical potential. Specifically, it will be shown, how water and protic solvent molecules self-organize in this environment and how they impact the thermodynamic state of the sorbed and reacting molecules as well as the state of the catalyst. As examples for catalytic transformations, the lecture will use monomolecular elimination reactions. The impact on catalysts will be discussed using supported metal particles in hydrogenation. Experimental methods to define the state of the reacting molecules combined with detailed kinetic analysis will be used to explain the principal contributions of the interactions and their influence on reaction rates.
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Professor of Chemistry and member of the Catalysis Research Institute at the Technische Universität München
Prof. Lercher’s research addresses fundamental aspects of catalysts and catalyzed reactions that enable catalysis to lower the carbon footprint via new approaches to synthesize energy carriers and chemical intermediates. The research is focused to realize catalyzed conversions at significantly lower reaction temperatures and with higher selectivity than possible today. Two aspects of enzyme sites, i.e., the tight fit of the space around the active site and the chemical functionality of this space, are used as guideline to synthesize novel catalysts. The in-depth characterization of the nature and structure of such catalytically active sites, of their chemical functionality and of the space around it, as well as of the molecules populating this space is the key to the successful realization of this strategy. The pores of catalysts and the molecules surrounding their active centers stabilize ground and excited states of reactants, intermediates, and products. Johannes studies the dynamic evolution of catalysts such as zeolites, molecular organic frameworks and supported metal catalysts throughout their lifespan and spectroscopically monitors changes during catalyst synthesis, sorption and reactions. The work combines advanced physicochemical methods to characterize the structure and electronic state of these materials as well as the reactions including IR, Raman, solid state NMR spectroscopy and X-ray absorption spectroscopy.
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