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

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.

Automated summary

In this study, Fe/CeO2 composite catalysts were designed to reduce the activation energy of the C-H bond and improve CH4 conversion. The existence of a solid-solution phase of Fe/CeO2 and a surface close-contact Fe2O3/CeO2 heterostructure was confirmed. Density functional theory calculations showed distinct charge accumulations on the substitutional-doped Fe sites, which effectively lowered the reaction energy of CH4 cleavage. The surface close-contact Fe2O3/CeO2 heterojunction improved carrier separation efficiency and photocatalytic performance.