Relationship between Acid–Base Properties and the Activity of ZrO₂‐Based Catalysts for the Cannizzaro Reaction of Pyruvaldehyde to Lactic Acid

Abstract

Abstract The Cannizzaro reaction of pyruvaldehyde to lactic acid is investigated in a flow reactor with ZrO 2 catalysts with different structures and acid–base properties. The results show that a difference in the crystalline structures of two ZrO 2 polymorphs strongly affects the conversion of pyruvaldehyde. The monoclinic phase of zirconia is the most active for this reaction. A good correlation is observed between the reaction rate and the concentration of Lewis acid sites of sufficient strength, which shows that these sites play a major role in the reaction. A reaction mechanism is proposed involving coordinatively unsaturated Zr 4+ cations as sites for activating pyruvaldehyde molecules, whereas Zr 4+ −O 2− pairs generate terminal OH groups through water dissociation.