Refinement of shale gas over the past several decades has produced an abundance of methane that is typically wasted by the practice of gas flaring. Research efforts have focused on identifying catalysts that can utilize this surplus methane by the production of ethane and ethylene. Solid oxide cells can form hydrocarbons by oxidative coupling of methane (OCM) with the advantage of producing electricity from the spontaneous reaction. We explored La0.7Sr0.2Co0.2Fe0.8O3 (LSCF) as an anode for OCM to C2 and C3 hydrocarbons. The in-situ exsolution of bimetallic CoFe nanoparticles and the resultant improvement on the electrochemical performance of the LSCF cell for OCM was supportively verified by analysis of surface and bulk characteristics as well as DFT calculations. LSCF was synthesized via a sol-gel method as described in our earlier publication. LSCF underwent the structural transformation under 5% H2/N2 at 850oC as demonstrated by XRD. The XRD diffraction lines of LSCF remained after 1 h of reduction at 850oC (H2-Red-LSCF), but additional features corresponding to bimetallic CoFe, LaSrFeO4, and La2O3 also emerged. Moreover, XRD analysis showed that the CH4-treated LSCF (CH4-Red-LSCF) experienced the same structural transformation as H2-Red-LSCF. TPD-DRIFTS using CO2 as a probe molecule conducted on LSCF and Red-LSCF verified that the surface of Red-LSCF is more basic than that of LSCF and the reduction is an effective way of promoting the catalytic characteristics of LSCF for the activation of CH4. In-situ CH4-DRIFTS were conducted on LSCF and Red-LSCF at 450°C to gain insight on the surface dynamics of CH4 activation. According to the results, CH4 coupling reaction to C2+ competes with the oxidation of CH4, and the oxygen supply is a key parameter for controlling the selective conversion of CH4. For OCM, 47–60% of C2+ hydrocarbon selectivity was obtained with 1–9% conversion of CH4 at different current densities.

In-situ exsolution of bimetallic CoFe nanoparticles on Co doped (La,Sr)FeO3 perovskite: Its effect on oxidative coupling of methane

ACS Spring 2022

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