Heterogeneity of polyoxometalates by confining within ordered mesopores: toward efficient oxidation of benzene to phenol

Abstract

Polyoxometalates (POMs) are a family of promising homogeneous catalysts for various processes. The design of POM-based heterogeneous catalysts, while important for real-world catalysis, is an important topic. Herein, a green and effective mechanochemical assembly strategy was developed to encapsulate the POM inside the ordered mesoporous polymer (OMP) with biomass tannin as the precursor. The strategy was realized by solid-state ball milling of the POM, using 3-aminophenol and tannin with F127 as the template, and removing the template by calcination. The POM-containing materials possessed uniform mesopores (5–10 nm) and high surface areas (150–250 m² g⁻¹). In particular, the H₅PM₁₀V₂O₄₀-based OMP exhibited good activity (33% conversion and 100% selectivity) and stability (reused in five runs) for the hydroxylation of benzene to phenol. The results of experiments and characterizations demonstrated that the unique confinement structure and the reversible V⁵⁺/V⁴⁺ redox pairs induced by the strong interaction between the OMP and PMoV may account for the good catalytic performance.