Uncovering Electrochemical Methane Oxidation Mechanism through the In Situ Detection of Reaction Intermediates
Tareq A. Al‐Attas, Karthick Kannimuthu, Mohd Adnan Khan, Md Golam Kibria
Abstract
The electrochemical partial oxidation of methane (CH 4 ) to value-added chemicals under ambient conditions provides a solution for harnessing abundant natural gas resources. Here, we investigate α-Fe 2 O 3 as a model catalyst to gain a mechanistic understanding of the electrochemical CH 4 oxidation reaction (eCH 4 OR). During chronoamperometric experiments, we obtain liquid products (formic acid, acetic acid, and acetone) with ∼6.5% total Faradaic efficiency at 2.3 V versus the reversible hydrogen electrode (V RHE ). At lower potentials below 2.0 V RHE, non-Faradaic CH 4 adsorption occurred, confirmed by in situ ATR-SEIRAS (attenuated total reflectance–surface-enhanced infrared absorption spectroscopy) and impedance spectroscopies. In addition to verifying the presence of the Fe IV O species, in situ spectroelectrochemical measurements revealed that CH 4 oxidation initiates via H-abstraction to form •OCH 3 species. The reaction undergoes further oxidation steps, leading to formate. Coupling between •OCH 3 and formate generates •OCOCH 3 species. Further, C–C coupling between – COCH 3 and – CH 3 resulted in acetone formation. Real-time proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) confirms the proposed pathways. Based on these observations, we propose a mechanistic pathway for selective CH 4 electrooxidation.