Understanding Pathways for Enhancing Catalytic Rates – 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.