Importance of V4+ and optimal acid environment in the hydroxylation of inert benzene via activation of Csp2-H bond

Hydroxylation of inert benzene through the activation of the C_sp2-H bond is a representative reaction about the transformation of C–H bonds to C–O bonds, which has far-reaching guiding significance but remains a challenging scientific problem. To overcome this problem, a series of VO_x-Ga₂O₃/SiO₂–Al₂O₃ were prepared to achieve an efficient and economical hydroxylation path of benzene to phenol. The results showed that the phenol yield was 72.89% (selectivity > 98.1%) under the optimum conditions. The reason is that the C–H bond in the benzene ring is activated by heterolysis over a VO_x-Ga₂O₃/SiO₂–Al₂O₃ catalyst. Meanwhile, the introduction of aluminum (Al) and gallium (Ga) made a qualitative change in the catalyst, enhancing the electron motion and spin motion of vanadium species, resulting in the increase of V⁴⁺/V⁵⁺ ratio. In addition, the catalyst can provide an optimal acidic environment and a three-dimensional cross-linked surface structure that facilitates product diffusion.