Enhanced Catalysis of Mechano-Chemically Synthesized KMgF3 Catalysts for the Knoevenagel Condensation

Abstract

The catalytic activity of KMgF₃ catalysts for a Knoevenagel condensation reaction was enhanced by synthesizing the catalysts mechano-chemically. The Brunauer–Emmett–Teller specific surface area and number of strongly basic site on KMgF₃ were increased by applying greater mechanical energy (i.e. a higher rotation rate) during the mechano-chemical process. These increases were caused by stronger mechano-chemical effects such as micronization of the particles and the introduction of lattice defects onto the surface, which resulted in an enhancement of the catalytic activity of KMgF₃ toward a Knoevenagel condensation reaction. X-ray photoelectron spectroscopic analysis revealed that the elemental composition of the KMgF₃ surface was similar to that for K₂MgF₄, indicating the possibility that the true active component for this reaction was K₂MgF₄ rather than KMgF₃. Kinetic measurements revealed that Knoevenagel condensation catalyzed by KMgF₃ was a first-order reaction with an estimated apparent activation energy of 55.8 kJmol⁻¹. A soluble component capable of acting as a catalyst was not present in the solution; the KMgF₃ acted as a true solid catalyst.