Dysprosium-doped zinc tungstate nanospheres as highly efficient heterogeneous catalysts in green oxidation of terpenic alcohols with hydrogen peroxide

A green route to oxidize terpenic alcohols (nerol and geraniol) with H2O2 over a solid catalyst was developed. The Dy-doped ZnWO4 catalyst was synthesized by coprecipitation and microwave-assisted hydrothermal heating, containing different dysprosium loads. All the catalysts were characterized through infrared spectroscopy, powder X-ray diffraction, surface area and porosimetry, transmission electronic microscopy image, and n-butylamine potentiometric titration analyses. The influence of main reaction parameters such as temperature, the stoichiometry of reactants, loads, and catalyst nature was assessed. ZnWO4 2.0 mol% Dy was the most active catalyst achieving the highest conversion (98%) and epoxide selectivity (78%) in nerol oxidation. The reaction scope was extended to other terpenic alcohols (i.e., geraniol, borneol, and alpha-terpineol). The highest activity of ZnWO4 2.0 mol% Dy was assigned to the lower crystallite size, higher surface area and pore volume, higher acidity strength and the greatest dysprosium load.