Direct Correlation of the Crystalline Phases of La _0.9 Sr _0.1 Co _{1– <i>y</i>} Fe <i> _y </i> O _3−δ with the Partial Oxidation of Methane via <i>In Situ</i> Neutron and Synchrotron Diffraction

Oxygen transport membranes find broad usage in many technologies, but due to the harsh conditions under which such technologies operate, detailed structural analysis under operational conditions has been limited. This work details the <i>in situ</i> neutron and synchrotron diffraction of the industrially relevant family of compounds, La_0.9Sr_0.1Co_1-<i>y</i> Fe <i>_y</i> O_3-δ (<i>y</i> = 0, 0.25, 0.75, 1), under reductive and oxidative conditions at elevated temperatures ranging from 723 to 1123 K. Quantitative Rietveld refinements determine the molar fraction of all crystalline intermediates and products that form during the reactions of La_0.9Sr_0.1Co_1-<i>y</i> Fe <i>_y</i> O_3-δ (<i>y</i> = 0, 0.25, 0.75, 1) with methane and then air. Coupling <i>in situ</i> diffraction analysis with catalytic product analysis of the partial oxidation of methane allows for the catalytically active phases to be determined. This work shows the strength of <i>in situ</i> diffraction under extreme conditions and the insights it can give about reactions in the solid state that have previously been elusive.