Synergistic combination of graphitic C3N4 and polyoxometalate-based phase-transfer catalyst for highly efficient reductant-free aerobic hydroxylation of benzene

Abstract

A facilely recyclable catalytic system towards liquid-phase reductant-free aerobic oxidation of benzene to phenol is built by simultaneously using graphitic carbon nitride (C3N4) and Ch5PMoV2. Especially, the hybrid Ch5PMoV2 is regarded as a temperature-controlled phase-transfer catalyst that prepared by modifying Keggin-type V-containing polyoxometalate anions (PMoV2) with choline (Ch) cations. The combined catalyst C3N4-Ch5PMoV2 shows a high activity with 10.7% phenol yield, 8.94 h−1 turnover frequency (TOF) and superior reusability under the optimized reaction conditions. Full characterizations and analyses including electron spin resonance spectroscopy (ESR), cyclic voltammetry (CV) and density functional theory (DFT) calculation are used to demonstrate the phase-transfer character and tuned redox property of Ch5PMoV2. Furthermore, a synergistic catalytic mechanism is proposed and discussed based on the experimental and DFT calculation results.