Sustainable Valorization of Methane into Formaldehyde via Atmospheric Gas-Solid Photothermal Catalysis Using a Diatomic Iron Catalyst.

Abstract

Gas-solid photothermal catalytic pathway for methane (CH₄) oxidation to formaldehyde (HCHO) at atmospheric pressure addresses product concentration limitations in high-pressure gas-liquid-solid batch systems. However, catalyst deactivation due to slow product desorption and oxygen replenishment remains a challenge. Here, inspired by methane monooxygenase, Fe₂ diatomic anchored ZnO catalyst (Fe₂-ZnO) were synthesized to addresses such challenge. The Fe₂ diatomic pairs enhance charge separation, promoting C-H bond of CH₄ cleavage, while their weak interaction with oxygen species facilitates *HCHO desorption, enabling gaseous HCHO production with the assistance of heat. Additionally, the strong interaction between Fe₂ pairs and ZnO enhances charge accumulation around the Fe₂ diatomic pairs, facilitating O₂ adsorption, activation, and oxygen vacancy replenishment. Thus, the Fe₂-ZnO catalyst achieves an HCHO production rate of 31.8 mmol g_cat^-1 h^-1 (71.7% selectivity) and superior stability (<10% activity loss over 50 h). And a concentrated HCHO solution (579.7 μmol mL^-1, 1.74 wt %) is obtained via water absorption at 0 °C for 12 h. These findings provide references for the application of diatomic catalysts in CH₄ conversion.