Ca/Al Mixed Oxides as Catalysts for the Meerwein-Ponndorf-Verley Reaction

Three hydrocalumites in a Ca/Al ratio of 2 were prepared by coprecipitation, the sol-gel method and homogeneous precipitation with urea. The solids thus obtained possess the typical structure of layered double hydroxides (LDHs), which, however, is lost by calcination at 450 °C. X-ray diffraction analysis and measurements of CO₂ thermal programmed desorption revealed that the calcination products were amorphous and that the particular form containing the largest number of basic sites was that obtained by coprecipitation. The calcined solids were tested as catalysts in the Meerwein-Ponndorf-Verley reaction of benzaldehyde and cyclohexanone with 2-propanol, and that containing the greatest number of basic sites was found to be the most active in the process. A mechanism for the process consistent with the results is proposed. Graphical Abstract [graphic removed]