Optimizing the surface distribution of acid sites for cooperative catalysis in condensation reactions promoted by water

Summary Addition of small amounts of water to the organic solvent may result in different promoting or inhibiting effects in aldol condensation reactions depending on the distribution of active sites on the surface. In a combination of liquid-phase catalytic activity measurements, spectroscopies, and theoretical calculations, we have shown that water clusters around the acid site can form bridges with a ketone molecule located close to the activated carbonyl on another site. When the distance between the two acid sites is greater than a distance corresponding to about two water molecules, the efficiency of the bond polarization of the ketone by a remotely located acid site decreases significantly, and the presence of water no longer promotes the reaction. This work provides a quantitative assessment of how solvent molecules can bridge isolated active sites to enable cooperative catalysis, which offers an additional dimension for engineering catalysis at the nanoscale.