Abstract
Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. The demand has increased further due to the recent discoveries of shale gas reserves. Oxidative and non-oxidative coupling of methane (OCM and NOCM) have been actively researched, although catalysts with commercially viable conversion rates are not yet available. Recently, {{{{{{{mathrm{Sr}}}}}}}}_2Fe_{1.5 + 0.075}Mo_{0.5}O_{6 - delta } (SFMO-075Fe) has been reported to activate methane in an electrochemical OCM (EC-OCM) set up with a C2 selectivity of 82.2%1. However, alkaline earth metal-based materials are known to suffer chemical instability in carbon-rich environments. Hence, here we evaluated the chemical stability of SFMO in carbon-rich conditions with varying oxygen concentrations at temperatures relevant for EC-OCM. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO3 was observed to be a major decomposition product along with SrMoO3 and MoC. Nevertheless, our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water.
Highlights
Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades
The CV measurement coupled with mass spectroscopic analysis indicated no ethylene production at potentials
CV measurements carried out in a wide operating window combined with mass spectra analysis demonstrate that methane could be activated at very low applied biases with respect to the cathode acting as reference electrode
Summary
Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO3 was observed to be a major decomposition product along with SrMoO3 and MoC. Our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water. OCM pioneered by Keller and Bhasin, on the other hand, suffers from overoxidation to CO2 and H2O as the partial oxidation products of methane such as ethane and ethylene are more active than methane creating selectivity challenges[8]. Our results indicate the possibility of EC-OCM to produce ethylene selectively at low overpotentials along with cogeneration of energy
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