Theoretical Study on Methane Oxidation Catalyzed by Fe/ZSM-5: The Significant Role of Water on Binuclear Iron Active Sites

Abstract

In the present study, density functional theory (DFT) calculations were performed to investigate the reaction mechanism of methane oxidation catalyzed by ZSM-5-supported binuclear iron species. A variety of binuclear iron sites such as [Fe(μ-O)Fe]2+, [Fe(μ-O)2Fe]2+, [Fe(μ-O)(μ-OH)Fe]+, and [HOFe(μ-O)FeOH]2+ were considered. The conversion of methane to methanol is decomposed into two processes: C–H activation and methanol formation. It is found that the anhydrous [Fe(μ-O)Fe]2+ sites exhibit the lowest reactivity for methane oxidation due to high energy barriers for both C–H activation and methanol formation steps, while the [Fe(μ-O)(μ-OH)Fe]+ and [HOFe(μ-O)FeOH]2+ sites are found to exhibit higher reactivity for methane oxidation in comparison with the anhydrous sites. This high reactivity is mainly attributed to the presence of the terminal or bridged hydroxyls, which can either provide a significant coordination effect or act as an oxidant for methane oxidation. Moreover, we find that on both [Fe(μ-O)Fe...