(619g) In-Situ Exsolution of Bimetallic Cofe Nanoparticles on (La,Sr)FeO3 Perovskite: Its Effect on Oxidative Coupling of Methane

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. One strategy is to use a membrane reactor for OCM operating at low partial pressures of oxygen. A further advantage of solid oxide cells is that electricity can be spontaneously generated during OCM.

We explored La_0.7Sr_0.2Co_0.2Fe_0.8O₃ (LSCF) catalyst as an anode for oxidative coupling of methane to ethylene and propylene. 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 underwent the structural transformation under reducing environment. The main XRD peaks of LSCF remained after 3 h of reduction (H₂-Red-LSCF), but the additional features corresponding to bimetallic CoFe, La2FeO₄, and La₂O₃ also emerged. Moreover, XRD patterns 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 were conducted on LSCF and Red-LSCF, and the results verified that the surface of Red-LSCF is more basic than that of LSCF and that reduction is an effective way of promoting the catalytic characteristics of LSCF for the activation of CH₄. Moreover, in order to gain insight into the surface dynamics during CH₄ activation, in-situ CH₄-DRIFTS measurements were conducted on LSCF and Red-LSCF catalysts under CH₄ atmosphere at 450^oC. According to the results, CH₄ coupling reaction to C₂₊ is competing with the oxidation of CH₄ and the controlled oxygen supply is a key parameter for a selective conversion of CH₄ on Red-LSCF.