First-principles microkinetic modeling of partial methane oxidation over graphene-stabilized single-atom Fe-catalysts

Abstract

Catalytic conversion of CH₄ to transportable liquid hydrocarbons via partial oxidation is a promising avenue towards efficient utilization of natural gas. Single Fe atoms on N-functionalized graphene (FeN₄/GN) have recently been shown to be active for partial CH₄ oxidation with H₂O₂ at room temperature. Here, density functional theory (DFT) calculations combined with mean-field microkinetic modeling (MKM) have been applied to obtain kinetic understanding of partial CH₄ oxidation with H₂O₂ to CH₃OH and CH₃OOH over FeN₄/GN. CH₃OH and CH₃OOH are found to be minor and major reaction products, respectively, with a selectivity in agreement with reported experimental data. The kinetic modeling reveals two pathways for CH₃OH production together with a dominant catalytic cycle for CH₃OOH formation. The selectivity is found to be sensitive to the temperature and H₂O₂ concentration, with the CH₃OH selectivity increasing with increasing temperature and decreasing H₂O₂ concentration. Turnover frequencies of both CH₃OH and CH₃OOH are found to decrease over time, due to a change in the Fe formal oxidation state from +6 to +4; Fe(+6) is more active, but less stable than Fe(+4). The present work unravels the detailed reaction mechanism for partial oxidation of methane by FeN₄/GN, rationalizes experimental observations and provides guidance for efficient room-temperature methane conversion by single-atom Fe-catalysts.