Synergistic effects of Fe-substitutional-doping and a surface close-contact Fe2O3/CeO2 heterojunction in Fe/CeO2 for enhanced CH4 photocatalytic conversion

Abstract

The cleavage of the first C–H bond is a great challenge in achieving CH₄ conversion. Herein, we designed Fe/CeO₂ composite catalysts with efforts to reduce the activation energy of the C–H bond and improve CH₄ conversion. Both X-ray diffraction spectra and high-resolution transmission electron microscopy images confirmed the coexistence of an Fe/CeO₂ solid-solution phase and the surface close-contact Fe₂O₃/CeO₂ heterostructure. Density functional theory calculations validate distinct charge accumulations on the substitutional-doped Fe sites, which effectively lowered the reaction energy of CH₄ cleavage to form *CH₃ through induced CH₄ asymmetric polarization. Moreover, the existed surface close-contact Fe₂O₃/CeO₂ heterojunction effectively, which was comprehensively studied by using the band structure and in situ X-ray photoelectron spectra, improved carrier separation efficiency and further improved photocatalytic performance. In situ Fourier transform infrared spectra indicated the steady stream of CH₄ adsorption and quick dissociation on the catalyst surface. For the optimized sample, a high C1 product yield of 10.56 mmol g_cat.⁻¹ h⁻¹ was achieved with the presence of H₂O₂, outperforming almost all previous reports as we know. This work elaborates the different roles of varied Fe sites in Fe/CeO₂ during the photocatalytic conversion of CH₄, which has guiding significance for the development direction of composite catalysts in the future.