Synergistic photocatalytic CH4 conversion to C1 liquid products using Fe oxide species-modified g-C3N4

Abstract

CH₄ direct conversion into high value liquid oxygenated products under mild experimental conditions is of great significance to solve both environmental and energy problems. Although great effort has been made, yield and selectivity of products remain challenging. Herein, a binary catalyst Fe species-modified g-C₃N₄ (denoted Fe₁-g-C₃N₄), was synthesized for direct photocatalytic CH₄ conversion into C1 liquid oxygenated products near room temperature (30 °C) with H₂O₂ as an oxidant. Under optimal experimental conditions, a high yield of C1 products of 16.52 mol mol_Fe⁻¹ h⁻¹ (2.95 mmol g_cat.⁻¹ h⁻¹) was obtained with a C1 product selectivity of 95.5% (HCHO + HCOOH selectivity of 62%). The highest C1 product yield could reach 42.68 mol mol_Fe⁻¹ if the reaction time was prolonged to 6 h, accompanied by a high HCHO + HCOOH selectivity and turnover number of 94% and 110, respectively. Furthermore, the Fe₁-g-C₃N₄ catalyst presented good stability and reusability after 4 cycle runs with negligible changes in the C1 product yield and selectivity. The greatly improved photocatalytic performance due to both increased H₂O₂ utilization and enhanced electron/hole separation efficiency was discussed. The possible radical reaction mechanism was studied by combining X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), in situ Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS) and radical scavenger experiments.