Integrating Lattice and Molecular Oxygen Pathways to Enhance Toluene Oxidation via Mn Substitution in Fe x Co3– x O4 Spinel

Abstract Activation of lattice oxygen and molecular oxygen critically governs the catalytic degradation of volatile organic compounds (VOCs), driving substantial research into harmonizing the bonding state of oxygen atoms in transition-metal oxides to facilitate VOCs abatement. However, the underlying mechanism of oxygen activation via cation substitution in spinel remains to be explored owing to its significant flexibility in both tetrahedral and octahedral sites. Herein, a Mn-substituted FexCo3–xO4 spinel catalyst was developed for promoting oxidation of toluene (one of the typical aromatic VOCs), with the temperature of 90% toluene conversion decreasing by approximately 51 °C relative to the pristine one. Multiple characterizations and theoretical calculations revealed that Mn3+ substitution at octahedral Co3+ sites of FexCo3–xO4 modulated the metal–oxygen bonds within the Mn–O–Co structure for activating surface lattice oxygen, accompanied by the creation of abundant oxygen vacancies for O2 excitation. The combined results of temperature-programmed analyses, isotopic labeling experiments, and in situ spectroscopy showed that the adsorbed toluene could be synchronously oxidized by activated lattice oxygen and chemisorbed oxygen generated via O2 activation, thereby accomplishing the deep oxidation of toluene. This study clarifies the synergistic role of lattice and molecular oxygen in toluene oxidation and affords a potential catalyst for environmental remediation.