Electrochemical Oxidative Coupling of Methane to Produce Higher Hydrocarbons Using Sr₂Fe_1.5Mo_0.5O_6-Δ Electrocatalysts

Abstract

Efficient conversion of methane to value added products such as olefins and aromatics has been in pursuit for the past several decades. The demand has increased further due to the recent discoveries of shale gas reserves (1). Oxidative and non-oxidative coupling of methane (OCM and NOCM) has been actively researched although commercially viable conversion rates have not been achieved with any catalyst yet. Electrochemical OCM is gaining attention due to its ability to control the oxide ion flux that will help reduce the over-oxidation of methane while also helping to activate methane. Recently, (SFMO-075Fe) has been reported to activate methane with a C2 product selectivity of 82.2% (2). However, alkaline earth metal-based materials are known to suffer chemical instability in carbon rich environments at elevated operating temperatures. Hence, we evaluated the chemical stability of SFMO-075Fe and SFMO in carbon rich conditions at temperatures relevance for EC-OCM. SFMO-075 showed wonderful methane activation properties but suffered poor chemical stability as observed in thermogravimetric and powder XRD measurements. XPS and XRD measurements revealed that SrCO3 as the major product along with MoC when SFMO is exposed to methane at 900°C. We further found that methane could be selectively activated towards partial oxidation products such as ethylene at low overpotentials while higher applied biases results in complete oxidation of methane to carbon dioxide and water. We report in this presentation our findings with SFMO along with potential benefits of EC-OCM for methane activation. References Schwach, X. Pan, and X. Bao, “Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects,” Chem. Rev., 117, 8497, 2017. Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., 10, 1173, 2019.