Oxidation of cyclohexene with hydrogen peroxide using zirconia-silica mixed oxides: Control of the surface hydrophilicity and influence on the activity of the catalyst and hydrogen peroxide efficiency

Zirconia-silica mixed oxides can be prepared by sol-gel under basic conditions to yield mesoporous solids. Surface modification with methyl groups is possible by addition of methyltriethoxysilane to the preparation mixture in an amount up to 80% of the silane precursor. The extent of methylation controls the surface area, the porosity, and the catalytic activity of the solids in the oxidation of cyclohexene with hydrogen peroxide to yield cyclohexandiol as the major product. An increase in surface methylation results in a fourfold increase in the specific activity and in up to 85% efficiency in the use of hydrogen peroxide. Use of tert-butylhydroperoxide as the oxidant is not viable, as catalysts lose almost completely their oxidation activity and it results in the almost complete decomposition of the oxidant. (C) 2002 Elsevier Science (USA).