In situ X-ray diffraction computed tomography studies examining the thermal and chemical stabilities of working Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes during oxidative coupling of methane

Abstract

In this study we present the results from two in situ X-ray diffraction computed tomography experiments of catalytic membrane reactors (CMRs) using Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) hollow fibre membranes and Na–Mn–W/SiO₂ catalyst during the oxidative coupling of methane (OCM) reaction. The negative impact of CO₂, when added to the inlet gas stream, is seen to be mainly related to the C₂₊ yield, while no evidence of carbonate phase(s) formation is found during the OCM experiments. The main degradation mechanism of the CMR is suggested to be primarily associated with the solid-state evolution of the BSCF phase rather than the presence of CO₂. Specifically, in situ XRD-CT and post-mortem SEM/EDX measurements revealed a collapse of the cubic BSCF phase and subsequent formation of secondary phases, which include needle-like structures and hexagonal Ba₆Co₄O₁₂ and formation of a BaWO₄ layer, the latter being a result of chemical interaction between the membrane and catalyst materials at high temperatures.