(530a) Understanding and Controlling Catalytic Chemistry in the Crowded Environment of Zeolites in Liquid Phase

Lercher, J. A., Pacific Northwest National Laboratory
The molecular sized pores of zeolites provide a unique chemical and steric environment for catalysis. The regular dimensions allow stabilizing ground and transition states of reacting molecules better than on larger pore oxide and organic porous materials, enhancing interaction strength and lowering the standard free energies of transition states in a highly selective manner. These properties are analogs to qualities critical for the high activity of enzymes, the local constraints and the local chemical environment at active sites. The presence of liquid phase induces complex ordering of reactants, intermediates and products enabling a subtle way to direct sorption and catalysis. Especially the ordering in protic solvents, such as water, leads to new chemistry as the zeolite transforms to a polar oxide environment with hydrated hydronium ions as the stable active site.

Water and protic solvent molecules self-organize in this environment and impact the thermodynamic state of the reacting molecules. The resulting interactions can be designed and controlled via direct synthesis (changing pore sizes and concentration of sites), as well as via the addition of cations, oxidic clusters or organic fragments. As examples for catalytic transformations elimination reactions of alcohols, alkylation of aromatic molecules and oligomerization of olefins will be compared. It will be discussed, how reaction rates and pathways can be optimized using the space available for transition states and the chemical constituents around the active site.