From Core-Shell to Yolk-Shell: Improved Catalytic Performance toward CoFe2O4@ Hollow@ Mesoporous TiO2 toward Selective Oxidation of Styrene

Developing catalysts with structural characteristics, reusability, cost-effectiveness, environmental friendliness, and preferable catalytic performance is challenging for the selective oxidation of alkenes. In this article, we report the synthesis of magnetically separable CoFe2O4@ hollow@ mesoporous TiO2 with yolk-shell structure, which could be used as a selectivity variable and stable catalyst for the selective oxidation of styrene, yielding different oxidation products. With oxygen as the oxidant, epoxidation of styrene occurred, affording an epoxy group. With hydrogen peroxide as the oxidant, oxidative cleavage of double bonds in the styrene and further oxidation were conducted, affording a carboxylic acid group. Compared with pristine CoFe2O4, TiO2, and CoFe2O4/TiO2 core-shell structure, the CoFe2O4@ hollow@ mesoporous TiO2 with yolk-shell structure was found to be a more efficient catalyst for the oxidation of styrene. Meanwhile, the kinetic analysis and activation energies of different catalysts were investigated to illustrate the relationship between the performance and the structure of catalysts. Active radical scavenging experiments were conducted to figure out the dominant radicals in the oxidation reaction. The corresponding possible reaction mechanisms of the oxidation reaction were also proposed.