Hydrated hydronium ions form at Brønsted acid sites in presence of water in zeolite pores of all sizes. The size of these clusters appears to be independent of the pore size and is limited by the entropy loss compared to condensation outside the zeolite pores. The remaining pore space is empty in the sole presence of water. The catalytic activity of these hydronium ions is determined by the steric environment and the ability to host organic molecules in the pores under these conditions. Molecules sorb in the space between hydronium clusters and – if smaller – also substitute for water in the cluster stabilizing the hydronium ion. Catalytic rates are influenced by the varying standard chemical potential of the sorbed substrates determined largely by the ionic strength of the environment and the interactions of the organic molecules by dispersion forces. Three examples will illustrate the impact of the hydronium ions on the catalytic rates, i.e., the dehydration of alcohols, the alkylation of aromatic molecules with alcohols, and the enhanced hydrogenation rates in presence of hydronium ions. In each of the cases, the hydronium ions act differently and the lecture will discuss, how reaction pathways change by the presence of the hydronium ions.

Catalysis by hydrated hydronium ions – the difference steric confines make

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.