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

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.