Electrocatalytic behaviour of CeZrOx-supported Ni catalysts in plasma assisted CO2 methanation

Abstract

Plasma-catalytic and thermo-catalytic methanation were assayed in the presence of a CeZrO_x-supported Ni catalyst, proving that high CO₂ conversions and high methane yields can be obtained under dielectric barrier discharge (DBD) plasma conditions and that they are maintained with time-on-stream over 100 h operating time. The characterization of the spent catalysts through TPD-MS, ATR-FTIR, TEM and HR-TEM and XRD evidenced the coexistence of a Ni⁰/NiO phase together with an increased presence of Ce³⁺ cations and oxygen vacancies, on the surface of the catalyst submitted to plasma catalytic operation. The different facts collected through physicochemical characterization point to our catalyst behaving like a PN junction, or like a fuel cell, with a P-side, the anode, i.e. the Ni-side releasing electrodes, while the CeZrO_x support, N-side and cathode, acts as an acceptor. The DBD plasma, rich in ionic species and free electrodes, acts as the electrolyte, conducting the electrodes in the right direction. Oxygen accumulation on the surface of the catalyst during thermo-catalytic methanation leads to the formation of non-reactive adsorbed species, whereas Ni-sintering is favored. Under DBD plasma conditions, electron transfer is guaranteed and the adsorption–desorption of reactants and products is favored.