This study investigated the use of a ceramic porous electrochemical reactor for the deep oxidation of propene. Two electrode composites, La0.85Sr0.15MnO3±d/Ce0.9Gd0.1O1.95 (LSM/CGO) and La0.85Sr0.15FeMnO3/Ce0.9Gd0.1O1.95 (LSF/CGO), were produced in a 5 single cells stacked configuration and used as backbone for the infiltration of materials able to modify the electrochemical and catalytic activity of the reactor. The catalytic activity of the reactor and the effect of polarization on the propene oxidation have been studied by gas analysis with a gas chromatograph (GC), during the reactor polarization at different reaction temperatures. The study of the effect of the infiltration of different electroactive materials on the electrode behavior has been carried on by the use of electrochemical impedance spectroscopy (EIS). Both the methods have been employed to understand the relationship between the catalytic activity of the reactor under polarization and the reactor electrochemical behavior. The impact of the morphology of the infiltrated material on the electrocatalytic activity was assessed by scanning electron microscopy. This project helped to better understand how the effect of polarization on propene conversion was a complex function of multiple variables: the microstructure of the backbone, the polarization resistance of the electrodes, both at OCV and under polarization, the electrical and morphological properties of the infiltrated material and the specific reaction conditions like the propene conversion. Although both the LSM/CGO and LSF/CGO backbones have demonstrated the ability to oxidize propene, the LSM/CGO exhibited the best performance both in terms of catalytic activity and faradaic efficiency for the propene oxidation. While LSF/CGO showed instability due to prolonged polarization, the LSM/CGO exhibited a strong electrode activation and increase of catalytic activity after the application of prolonged polarization. The infiltration of LSM/CGO backbone with Ce0.9Gd0.1O1.95, heat treated at low temperature to form a continuous layer on the electrode, was the best compromise to obtain high propene conversion at open circuit voltage together high rate enhancement ratio and faradaic efficiency values at low temperatures (300-350 °C). Although some stability problems affected the performance of multiple infiltrated Ce0.9Gd0.1O1.95 on LSM/CGO backbone, the strong activation of LSM upon prolonged polarization was able to partially counteract the instability of the infiltrated Ce0.9Gd0.1O1.95. This project demonstrated the possibility to enhance the oxidation of propene by polarization in a porous ceramic reactor. The infiltration of different active materials helped to increase the catalytic activity at open circuit voltage and the effect of polarization on propene oxidation rate at low temperature. The future development of this technology will see the infiltration of an active catalyst towards propene oxidation together with a NOx storage compound for the simultaneous oxidation of propene and the reduction of NOx with high efficiency.
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Kammer Hansen, Kent, Christensen, Henrik
Department of Energy Conversion and Storage, Technical University of Denmark, 2013