Single-iron catalyst with heterogenized TEMPO for selective toluene electrooxidation to benzaldehyde at low potentials

Abstract

Toluene electrooxidation offers a sustainable route for the synthesis of valuable oxygen-containing chemicals, but existing methods often rely on strongly acidic or basic electrolytes, high cell voltages, or soluble mediators that complicate catalyst separation and increase waste. In this study, we show that combining grafted 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) units with atomically dispersed iron sites in nitrogen-doped carbon enables efficient and selective electrooxidation of toluene to benzaldehyde under mild conditions. The catalyst operates at low potentials of 1.5 ~ 1.8 V vs. Ag/Ag⁺ without the need for added molecular hydrogen-atom-transfer reagents, soluble metal redox couples, or strong acids/bases. Mechanistic studies indicate that the grafted TEMPO not only participates in oxidation chemistry but also reshapes the carbon framework by introducing carbonyl groups, which modulate the electronic structure and lower the spin state of the iron centers. These coupled electronic and spin effects promote oxygen activation, thereby promoting the formation and release of reactive superoxide species that drive selective toluene oxidation. This strategy provides a cleaner platform for aerobic electrooxidation and offers a design principle for selective oxidation catalysis powered by electricity.