Hydroxylation of Benzene to Phenol by H2O2 over an Inorganic–Organic Dual Modified Heteropolyacid

Abstract

Various catalysts, including the heteropolyacid (HPA) H4PMo11VO40, its cesium salts, and inorganic–organic dual modified HPA catalyst, were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (13C NMR), N2 adsorption, acid–base titration, electron spin resonance (ESR) and X-ray diffraction (XRD) techniques as well as elemental analysis. These prepared catalysts were used in the hydroxylation of benzene to phenol by H2O2 as oxidant. The inorganic–organic dual modified HPA Cs2.5(MIMPS)1.5PMo11VO40, prepared by partially exchanging Cs+ with protons in H4PMo11VO40 and followed by the immobilization of 3-(1-methylimidazolium-3-yl)propane-1-sulfonate (MIMPS), led to a liquid–solid biphasic catalysis system in the hydroxylation, which showed the best catalytic performance in terms of reusability and catalytic activity. The high reusability of Cs2.5(MIMPS)1.5PMo11VO40 in the heterogeneous hydroxylation was probably due to its high resistance in leaching of bulk HPA into the reaction medium. The slightly enhanced catalytic activity for the catalyst was due to the acid sites available from MIMPS beneficial to the hydroxylation.