Selective oxidation of benzene to phenol by FeCl3/mpg-C3N4 hybrids

Abstract

Existing phenol production mostly by cumene processes is a three-step route with unwanted acetone as by-product. Here, we report the FeCl₃ and mesoporous carbon nitride hybrid (FeCl₃/mpg-C₃N₄) as an active and selective photocatalyst to activate H₂O₂ for the oxidation of benzene to phenol under visible-light illumination. By fine-optimizing FeCl₃ loading amount in catalyst and reaction conditions, the one-step process achieved a 38% benzene conversion with 97% selectivity for phenol. The excellent catalytic performance of FeCl₃/mpg-C₃N₄ should be attributed to the fast reduction of Fe³⁺ to Fe²⁺ by photo-irradiated electrons from mpg-C₃N₄. To further understand the reaction route, several electron spin resonance (ESR) tests were carried out, confirming mpg-C₃N₄ promoted redox cycle of Fe²⁺/Fe³⁺ in the FeCl₃/mpg-C₃N₄ system. Based on these results, a catalytic mechanism for the oxidation of benzene by FeCl₃/mpg-C₃N₄ hybrids was provided. This environmental-friendly and efficient method is expected to open up a new avenue for one-step phenol preparation.