Microporous Zirconia–Silica Mixed Oxides Made by Sol–Gel as Catalysts for the Liquid-Phase Oxidation of Olefins with Hydrogen Peroxide

The preparation of a series of microporous zirconia–silica mixed oxides by sol–gel is reported. These have been characterized by BET methods, thermogravimetric analysis, X-ray diffraction analysis, UV–vis spectroscopy, and TPD of ammonia. The materials have high surface areas; they are amorphous and possess only mild surface acidity. They have been tested in the oxidation of different substrates with hydrogen peroxide, particularly the oxidation of cyclohexene. The catalysts are moderately active and produce mainly products arising from oxirane ring opening, particularly when the reactions are carried out in the absence of solvent. The use of a less hydrophilic reaction medium and/or the partial methylation of the silica surface tend to increase the reaction productivity and reduce hydrogen peroxide consumption.