LPP - Laboratoire de Physique des Plasmas - UMR 7648 - Carolina Garcia Soto a soutenu sa thèse "Fundamental study of plasma-catalytic surface interactions for CO2 conversion and application of fluidized bed reactors"

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Accueil > A propos du LPP > Communication > Actualités archivées > 2023 > Carolina Garcia Soto a soutenu sa thèse "Fundamental study of plasma-catalytic surface interactions for CO2 conversion and application of fluidized bed reactors"

Carolina Garcia Soto a soutenu sa thèse "Fundamental study of plasma-catalytic surface interactions for CO2 conversion and application of fluidized bed reactors"

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Le 28 avril 2023, Carolina Garcia Soto a soutenu sa thèse "Fundamental study of plasma-catalytic surface interactions for CO2 conversion and application of fluidized bed reactors".

Abstract :
The increase in global temperature has led to seek the reduction of carbon dioxide emissions and by closing the carbon cycle CO2 can be transformed to platform molecules. Non-thermal plasmas can provide a peculiar environment out of equilibrium allowing for CO2 conversion with minimal energy cost. Coupling the plasma with a catalytic material could offer a significant advantage by improving the conversion performance and the selectivity. Fluidized bed (FB) reactors are an innovative way to combine a plasma and a catalyst for CO2 conversion by improving the surface contact area with the gas/plasma phase and the heat transfer. This work consists on the one hand of studying the plasma/catalyst interaction from a fundamental point of view, and on the other hand of understanding the specific mechanisms that can intervene in a fluidized bed plasma reactor configuration in order to ultimately improve its performance.
If the plasma can provide reactive species to trigger chemical reaction on the catalytic surface, the catalyst can also affect the plasma development. To understand the complexity of this mutual interaction dedicated experiments at low pressure allowing for time resolved measurements of both adsorbed and gas phase species were first performed before analyzing the performances of atmospheric pressure reactors.

DC glow discharges at low pressure (1-6 mbar) were first used due to the homogeneity of the plasma and the previous plasma kinetic studies done in similar configuration. The plasma-catalytic surface reactions were studied in detail on CeO2 during CO2 only and CO2-CH4 plasma by in situ FTIR transmission experiments. Carbonates species were identified upon exposure to CO2 gas. During CO2 plasma, the phenomenon of "plasma-assisted desorption" was further clarified by identifying three main contributions : increase in temperature, variations in partial pressures but also effect of short live excited species specific to plasma exposure. The same studies under CO2-CH4 plasma highlight the formation of formates by reaction between carbonates and hydroxyls adsorbed on the surface of CeO2. This same mechanism is suggested by ex situ experiments carried out at the University of Bucharest using a Dielectric Barrier Discharge (DBD) reactor at atmospheric pressure and DRIFTS for surface analysis. These results lay the groundwork for identifying the type of reaction mechanism that would improve catalysts suitable for CO2 conversion.

The study of CO2 plasma interacting with a fluidizing catalytic material has also been done first in a DC glow discharge - FB reactor before looking at the performance of a FB-DBD at atmospheric pressure. The FB-glow discharge was investigated with and without Al2O3 particles with aid of Optical Emission Spectroscopy. The interaction of a chemically inert material in the discharge zone has a special interest to highlight the influence of the particles on the properties of the plasma. The results indicate a decay in Oxygen atom density through the fluidization of Al2O3 probably to an increase in the available surface where O recombine into O2 potentially preventing the reverse reaction. At the same time, the CO concentration increases, which is confirmed by FTIR spectroscopy analysis of the downstream gas. In addition, temperature of rotation was calculated by CO Angstrom system. The temperature does not increase significantly although the presence of Al2O3 particles seems to constrain the plasma spatially. This increase in performance is also observed in DBD at atmospheric pressure comparing fluidized bed to a packed bed configuration under the same conditions. Even without catalytic activity, Al2O3 has a physical effect modifying the chemistry and therefore, improving the conversion of CO2.

By comparing low-pressure discharges, which allow in situ measurements, with the performance of atmospheric pressure reactors, this work was able to highlight the role of the excited states produced by the plasma on the reactivity on the surface of the catalyst, and the influence of the presence of dielectric particles on the conversion of CO2 in the plasma itself. The specificities of the plasma/catalyst coupling and the advantages they can bring for an efficient conversion of CO2 could thus be identified to allow future optimization of fluidized bed plasma reactors, which are proving very promising.

Jury :
President : François Ozanam, Dir. de recherche, CRNS, École polytechnique
Rapporteur : Frédéric Thibault-Starzyk, Dir. de recherche, CNRS, ENSICAEN, Université de Caen
Rapporteur : Maria Victoria Navarro Lopez, Tenure Researcher, Instituto de Carboquimica, CSIC, Spain
Examinateur : Vasco Guerra, Associate Professor, Instituto Superior Técnico, Portugal
Examinateur : Maria del Carmen Bacariza Rey, Researcher, Instituto Superior Técnico, Portugal
Examinateur : Camelia Bala, Professor, University of Bucharest, Romania
Supervisor : Olivier Guaitella, Ing. de recherche, ́Ecole polytechnique, LPP
Co-Supervisor : Vasile I. Parvulescu, Professor, MC Romanian Academy, University of Bucharest, Romania

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Carolina Garcia Soto a soutenu sa thèse "Fundamental study of plasma-catalytic surface interactions for CO2 conversion and application of fluidized bed reactors"