Relationships between Phenol Production Activities and Lewis Acid Sites of Cu/HZSM-5 Catalyst for Gas-phase Aerobic Benzene Oxidation

Abstract

The currently used cumene method of producing phenol is a multistep reaction that requires costly production facilities and a large amount of energy, and thus, a simpler, greener method of phenol production must be developed. This study investigates the acidic properties of HZSM-5 and redox cycle of Cu to examine the mechanism of phenol formation via the gas-phase catalytic oxidation of benzene over the Cu/HZSM-5 catalyst. Pyridine adsorption Fourier transform infrared spectroscopy suggests that calcination at a high temperature (1273 K) leads to the dealumination of Cu/HZSM-5, and extra-framework Al increases the number of Lewis acid sites, which function as benzene activation sites. Photoluminescence spectroscopy indicates that the redox cycle of Cu comprises the reduction of Cu²⁺ to Cu⁺ by benzene and the oxidation of Cu⁺ to Cu²⁺ by O₂. Based on these results, the mechanism of phenol formation from benzene is inferred, and this study paves the way for the establishment of the economical, green industrial synthesis of phenol.