Catalytic evaluation of mesoporous metal oxides for liquid phase oxidation of styrene

Mesoporous manganese oxide, cobalt oxide, and hybrid Mn-Co oxide were synthesized using an inverse surfactant micelle method. The synthesized materials were monodispersed nanoparticle aggregates with connected and well defined intra-particle voids. An increase in the pore and crystallite size with increase in calcination temperature was observed with TEM, SEM, p-XRD, and N₂-sorption. These mesoporous metal oxides were employed in the selective oxidation of styrene using tert-butyl hydrogen peroxide as an oxidant. Higher selectivity towards styrene oxide was achieved using manganese oxide followed by cobalt oxide while the hybrid oxide showed the lowest selectivity towards styrene oxide. The catalytic activities of the compared catalysts were decreasing in the order of Mn-Co_350 (66.6 h⁻¹) > MnO₂_350 (47.4 h⁻¹) > Co₃O₄_350 (35.6 h⁻¹). The catalytic activities and selectivity profiles under various reaction conditions such as solvent type, catalyst amount, styrene to TBHP ratio and temperature are discussed. The catalytic recyclability of metal oxides showed that they are stable, and the structure of the catalyst was retained.