Enzyme-mimetic functional synergistic strategy of Mn-based spinel catalysts: Regulating oxygen vacancies and radical pathways to promote photocatalytic methane oxidation to C1-C2 oxygenates

The photocatalytic conversion of methane into valuable liquid oxygenates presents a promising strategy for advancing a sustainable chemical industry. However, achieving both high conversion efficiency and high selectivity using non-precious metal catalysts under ambient conditions remains a significant challenge. Inspired by the functional characteristics of natural enzymatic catalytic systems, this study has constructed a multicomponent synergistic catalytic system with ZnMn₂O₄ as the support. Through the defective engineering design of fluorine doping and in situ growth of tungsten species, it achieves efficient construction of the microenvironment of active centers and precise regulation of free radical intermediates. The optimized 3W20F-ZnMn₂O₄ catalyst achieved a liquid-phase product yield (including methanol and ethanol, etc.) of 442.02 μmol·g⁻¹ ·h⁻¹ with a selectivity of 98.6 % under ambient temperature and pressure—surpassing the performance of most reported non-precious metal-based catalytic systems. Studies have demonstrated that catalysts doped with the two elements exhibit significant differences in the oxygen sources of products, which reflects the distinct pathways they follow in catalyzing methane oxidation. Specifically, the oxygen vacancy (FVo) sites formed by F doping primarily adhere to a single reaction pathway using water as the oxygen source, where the active oxygen species are mainly dominated by ·OH generated from the dissociation of water molecules, ultimately yielding ethanol and small amount of methanol. In contrast, the active sites formed by W doping involve multiple reaction pathways. The production of ethanol relies more on ·OH from water molecule dissociation, while the generation of methanol and methyl hydroperoxide is more dependent on active oxygen species derived from oxygen activation. This study deepens the understanding of the multi-element synergistic catalytic mechanism and lays a foundation for the development of sustainable and efficient catalytic systems.