Influence of the coordination on the catalytic properties of supported W catalysts

Zirconia supported W catalysts were prepared using anionic exchange from a peroxo-tungstate solution and zirconium hydroxides of high surface areas. These solids contain about 20 wt% W, and retain a surface area of about 120 m2/g after calcinations in air at 873 K, temperature at which their acidity is maximum. Raman spectroscopy shows the presence of tetrahedral W at low temperature, sintered to polytungstates by calcination at 873 K and WO3 at 973 K. These catalysts are active for the oxidation of dibenzothiophene by hydrogen peroxide. The solids containing tetrahedral W cations show higher activity than clusters of WO3. The reaction can be performed with good oxygen selectivity with H2O2 in 2-butanol as solvent, or in decane with tert-butylhydroperoxide as oxidizing agent. The catalysts can be recycled without loss of performances.