Visible light promoted aerobic selective photo-oxidation of cyclohexene on LaCo_xCu_1−xO₃ catalyst

Heterogeneously catalyzed liquid oxidation of olefins with O₂ provides an alternative way for synthesizing high-value added chemicals. Herein, we report a straightforward urea-redox and sol-gel process for synthesizing LaCo_xCu_1−xO₃ for aerobic photo-oxidation of cyclohexene. Our research highlights a marked increase in the proportions of Co²⁺ and Cu⁺ species in a low chemical state, as well as enhanced visible light absorption through this method. Mechanistic investigations suggest that the catalytic process, particularly with LaCo_0.7Cu_0.3O₃, involves a radical pathway mediated by reactive oxygen species. The presence of Cu⁺/Co²⁺ species and surface oxygen vacancies is proposed to boost O₂ adsorption and activation on the catalyst, facilitating the formation of 2-cyclohexene-1-hydroperoxides. Furthermore, Cu²⁺/Co³⁺ species are thought to aid in generating cyclohexene-derived radical species. The efficient aerobic oxidation of cyclohexene on LaCo_0.7Cu_0.3O₃ catalyst relies on the formation of reactive oxygen species and carbon radicals, facilitated by its strong visible light illumination. It achieves a cyclohexene conversion of 89.4% and selectivity to cyclohex-2-ene-1-one of 72.2%, along with stable recyclability after six reuses. The creation of nano-structured LaCo_xCu_1−xO₃ through the urea-redox and sol-gel process offers a promising avenue for the development of highly efficient catalysts for the aerobic photo-oxidation of cyclohexene to cyclohex-2-ene-1-one in the future.