Electronic structure regulation of halogen anion-intercalated MgAl-LDH for highly selective photothermal oxidation of CH4

Abstract

The selective oxidation of methane (CH₄) into high value-added chemicals such as CO is one of the important challenges in the C1 chemical industry owing to the high bond energy of CH₄ (434 kJ mol⁻¹). Considering that Mg–O sites are the active sites for CH₄ activation, we report herein the successful fabrication of a series of halogen anion-intercalated MgAl-LDHs and the as-prepared MgAl-x (x = F, Cl, Br, I) have been fully characterized by various spectroscopic studies. When applied for the photothermal oxidation of CH₄, MgAl-F exhibits 86.5% selectivity for CO, while MgAl-I shows only 15.8% selectivity for CO. The O K edge XAS and XPS results show that F⁻ can significantly improve the charge density of the surface O–H bond on the MgAl-LDH laminates. In situ diffuse reflectance-infrared Fourier-transform spectroscopy (DRIFTS) demonstrates that MgAl-F can stabilize *CH₃ and release *CO species during the photooxidation of CH₄, which is favorable for the production of CO. DFT calculations demonstrate such a high selectivity for CO by MgAl-F can be attributed to favorable energy barriers of two key steps (*CH₃ to *CH₂ and *CO to *HOCO).