C. Athanasiou

Methane activation on a La0.6Sr0.4Co0.8Fe0.2O3 perovskite catalytic and electrocatalytic results

The catalytic and electrocatalytic behavior of the La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) perovskite deposited on yttria-stabilized zirconia (YSZ) was studied during the reaction of methane oxidation. Experiments were carried out in a well-mixed (CSTR) reactor at atmospheric pressure, in the 600–900°C range. When, instead of co-feeding with methane in the gas phase, oxygen was electrochemically supplied as O2−, considerable changes in the methane conversion and product selectivity were observed. Catalytic and electrocatalytic results were compared to those obtained when the LSCF served as a dense mixed-conducting membrane supplying oxygen to the methane feed stream because of the oxygen partial-pressure gradient across the membrane.

Catalytic and electrocatalytic oxidation of methane on palladium electrodes in a solid electrolyte cell

The catalytic oxidation of methane on polycrystalline palladium films was studied at 550-750°C and atmosheric total pressure. The reaction was studied under both open and closed-circuit. Under open circuit, and when yttria-stabilized zirconia (YSZ) was used as solid electrolyte, the technique of Solid Electrolyte Potentiometry (SEP) was used to monitor the thermodynamic activity of oxygen adsorbed on the Pd electrode during reaction. The main products were those of complete oxidation, i.e. CO2 and H2O. Under closed-circuit, the effect of electrochemical oxygen “pumping” to or from the catalyst was studied. Non-faradaic (NEMCA) phenomena were observed but the reaction rate enhancement factors (A) were not as large as with previously studied catalytic systems.

Modelling of solid oxide proton conducting reactor-cells: thermodynamics and kinetics

A model is prepared for hydro- and dehydrogenation reactions that are carried out in solid electrolyte cell-reactors. Hydrogen is supplied in the form of H+ through the proton conducting wall and the thermodynamic activity of hydrogen on the catalyst surface is controlled electrochemically. Three reactor types are considered, a plug flow reactor, a well-mixed reactor and a “single-chamber” cell in which both electrodes are exposed to the same reacting mixture. Under certain conditions, the yield of the cell-reactor is orders of magnitude higher than that of the corresponding conventional catalytic reactor. The key parameters that affect the product yield as well as the conditions that must be met, are discussed. Experimental results for the reaction of methane dimerization studied with a strontia-ceria-ytterbia electrolyte on palladium electrodes, are presented and compared to model predictions.

Electrode polarization at the O2(g), Pd/YSZ interface

Abstract The polarization phenomena of the O 2 –Pd–YSZ interface were studied as a function of oxygen partial pressure (1–100 kPa) and temperature (400–550°C) in the double chamber reactor cell: Pd|YSZ|Pd. The steady-state current–overpotential characteristics can be analyzed with a Butler–Volmer type of equation. The apparent anodic and cathodic charge transfer coefficients are found close to 0.5 and the activation energy of the exchange current was found to be about 107 kJ/mol. Based on the experimental results, a charge transfer reaction model, is proposed.

Methane activation on a La0.6Sr0.4Co0.8Fe0.2O3 perovskite; catalytic and electrocatalytic results

The catalytic and electrocatalytic behaviour of the La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) perovskite deposited on yttria stabilized zirconia (YSZ), was studied during the reaction of methane oxidation. Experiments were carried out at atmospheric pressure, and at temperatures between 600 and 900 °C. When, instead of cofeeding with methane in the gas phase, oxygen was electrochemically supplied as O2−, considerable changes in the methane conversion and product selectivity were observed. The non-faradaic effects (NEMCA) were also studied and compared to those observed with metal catalysts.

Evaluation and use of the Pd | SrCe0.95Yb0.05O3| Pd electrochemical reactor for equilibrium-limited hydrogenation reactions

The current — overpotential characteristics of the H2 - Pd - SCY interphase have been studied at atmospheric total pressure and temparatures between 400 – 550 °C in the single chamber reactor — cell: Pd | SCY | Pd. The results of I−η measurements indicate that the apparent anodic and cathodic charge tranfer coefficients are equal to: αa=αc=0.5. The present results are compared to those obtained with the single — chamber reactor cell: Ag | SCY | Ag. A solid state proton (H+) conducting reactor — cell with Pd electrodes was tested for the ammonia synthesis from its elements at atmospheric pressure. At 570 °C, over 75% of the ectrochemically supplied hydrogen was converted into NH3. The thermodynamic requirement for a high pressure process was eliminated.