Effect of Morphology on the Performance of Nb2O5 Catalysts for Thioether Oxidation at Room Temperature under Solvent-free Conditions

Nb2O5 catalysts with different morphologies were synthesized and used for thioether oxidation at room temperature under solvent-free conditions with H2O2 as the oxidant. Selective formation of sulfoxides in good to excellent selectivities was realized using spherical Nb2O5 as the catalysts. Selective formation of sulfones with excellent selectivities was achieved with layered Nb2O5 as the catalysts. Nb2O5 catalysts with different morphologies possessed different surface areas and acid amounts. A non-radical mechanism with Nb(OO) as the possible reactive oxygen species is proposed for thioether oxidation over spherical or layered Nb2O5 catalysts. Both the spherical and layered Nb2O5 catalysts demonstrated excellent reusability. There were no obvious changes for their catalytic performance after being recycled for ten runs. This study illustrates a means to modulate the catalytic activity for H2O2-based catalytic reactions by changing the catalyst morphology.