Heteropolyanion-based ionic hybrid solid: A green bulk-type catalyst for hydroxylation of benzene with hydrogen peroxide

A novel heteropolyanion-based ionic hybrid was prepared by combining the divalent ionic liquid (IL) cation of 1,1'-(butane-1,4-diyl)-bis(3-methylimidazolium) with the Keggin-structured V-containing heteropolyanion, and characterized by ¹H NMR, FT-IR, ESI-MS, XRD, SEM, TG, BET surface area, melting point, and elemental analysis. Its catalytic activity was evaluated in the hydroxylation of benzene with aqueous H₂O₂, including the testing of the influence of organic cations, catalytic reusability and optimization of reaction conditions. This hybrid is characterized to be semi-amorphous nanoparticles with a IL-like composition. The hybrid catalyst leads to the liquid-solid biphasic reaction system for hydroxylation of benzene with H₂O₂, presenting such advantages as high catalytic activity, convenient recovery, and steady reuse. The strong ionic interaction between the divalent IL cation and the heteropolyanion is responsible for the catalyst's solid nature and insolubility, and moreover, the bulk-type catalysis involving the V⁵⁺/V⁴⁺ redox pairs as active centers accounts for the hybrid's excellent catalytic performance.