(464b) Impact of Water on Acid-Base Catalyzed Reactions

Water is an increasingly important constituent as solvent, part of the reacting mixture and is nearly ubiquitous in acid-base reactions paralleling electrocatalytic transformations. Four aspects are critical, i.e., (i) water interacts and competes with reactants at active sites, (ii) water forms stable hydrated hydronium ions at surfaces and in pores differing in size and acid strength depending on the environment, (iii) hydronium ions as well as hydrated anions change the thermodynamic activity of interacting and reacting, and (iv) water tends to act corrosively at reactive interfaces as it changes the organization and chemical nature of (oxidic) surfaces. The first three aspects will be discussed using examples of sorption and Brønsted acid site catalyzed dehydration of alcohols for gas-solid and liquid-solid environments. It will be shown, how water changes the reaction pathways (altering, stabilizing and de-stabilizing interactions and transition steps) of almost all reaction steps. For gas-solid reactions stabilization of ground states rather than competition for acid sites reduce the rates for dehydration. For hydrated hydronium ions formed in presence of water the impact on the thermodynamic activity of the reacting substrate has a major impact on all interactions and reactive transformations. Strategies to use constrained environments for selectively enhancing reaction rates in these environments will be described.