Doping Effect of Zirconia with Lanthanum for the Selective Oxidation Reaction of Thioanisole

Abstract

La-doped ZrO2 catalysts were prepared by varying the lanthanum metal precursor in order to obtain 0, 3, and 5 wt.%. The resulting materials were fully characterized and evaluated their catalytic and selectivity performance in the oxidation of thioanisole with hydrogen peroxide as oxidant under mild reaction conditions. Doping of zirconia oxide with lanthanum improves the selectivity toward sulfone in the oxidation of thioanisole (71.9% selectivity, 5LaZr catalyst vs. 51.3% selectivity, Zr), due to modifications in the surface acid–base properties of zirconia, among other changes. From XRD profiles, the relative crystallinity of these solids decreases as the lanthanum doping increases. This favors oxygen mobility, which is a desirable feature for oxidation reactions. In addition, the presence of carbonate species for 5LaZr also participates, favoring the sulfone selectivity. Reaction parameters such as lanthanum content, nature of solvents, catalyst amount, temperature, oxidant amount, and reuses were evaluated.