BACKGROUND Control of greenhouse gas emissions has become one of the most important challenges faced by humanity. Among the various approaches to mitigating CO2 emissions, carbon capture and storage (CCS) is considered one of the most promising clean coal options for the future because it can be implemented in the short and medium terms at the industrial scale. Among CCS techniques, oxy-combustion offers advantages in using pure oxygen (O-2) as a comburent, where in a flue gas composed mainly of CO2 and water vapor is generated. Cryogenic air separation is the only available technology that can provide the required amount of O-2, but this process requires large amounts of energy and is costly, which make its large-scales implementation difficult. RESULTS In this framework, oxygen transport membranes are being researched as an O-2 supplier unit because they offer advantages from a techno-economic view point. In the present work, the thermochemical stabilities of La0.6Sr0.4Co0.2Fe0.8O3 and Cobalt-doped Ce0.9Gd0.1O were evaluated to obtain information on their behavior in oxy-combustion atmospheres. Experiments were performed in a circulating fluidized bed boiler of a pilot plant using an experimental sampling train. Samples of the two materials were characterized by X-ray diffraction, X-ray fluorescence, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller analysis. CONCLUSIONS The results revealed that both materials were susceptible to the presence of species that originated from flue gas, materials comprising the boiler and ducts, and coal ash, and that the CGO_Co material showed better performance than the other studied material. (c) 2020 Society of Chemical Industry