Electrochemical promotion of CH4 oxidation on Pd

Abstract

Abstract. The effect of Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) or Electrochemical Promotion (EP) was used to promote the methane oxidation reaction to CO2 and H20 over Pd polycrystalline films interfaced with yttria-stabilized zirconia in galvanic cells of the type: CH4, O2, CO 2, Pd/YSZ/Au, CH 4, 02, CO2It was found that by applying positive potentials or currents and thus, supplying O 2-onto the catalyst surface, up to 90-fold increases in CH 4 oxidation catalytic rate can be obtained. The induced changes in catalytic rate were two orders of magnitude higher than the corresponding rate of ion transfer to the catalyst-electrode surface, i.e. faradaic efficiency A values above 100 can be attained. The reaction exhibits electrophobic behavior under the experimental conditions of the investigation. The results can be rationalized on the basis of the theoretical considerations invoked to explain NEMCA behavior, i.e. the effect of changing work function on chemisorptive bond strengths of catalytically active electron donor or acceptor adsorbates.

Electrochemical Promotion of CH4 Combustion over a Pd/CeO2–YSZ Catalyst

“…Conse- quently, the catalytic reaction rate was increased by anodic polarisation, exhibiting electrophobic behaviour [8]. This result totally agrees with other electrochemical promotion studies on methane combustion, reported by Giannikos et al [17] and Roche et al [34]. These authors also observed electrophobic behaviour under oxidising conditions over palladium catalysts prepared by paste and sputtering, respectively.…”

“…As shown in Figure 8, the rate enhancement ratio was of 5.6. The Faradaic efficiency value was found to be 764 (the highest value reported for the electrochemical promotion of this reaction [17,[33][34][35]). This difference could be explained by the role of ceria film.…”

“…SEM, XRD and AC impedance spectroscopy were used to study the double electrolyte system. Electrochemical promotion of methane has been mainly reported on palladium supported over YSZ [17,33,34], but also on platinum [35]. Under oxidising conditions, it was observed in the literature that the reaction exhibited electrophobic behaviour, i.e.…”

Electrochemical promotion of deep oxidation of methane on Pd/YSZ

“…Owing to the catalytic properties, Pd2 is expected to have the most suitable microstructure. The increase in reaction rate of methane on Pd/YSZ under anodic polarization was already observed by Giannikos et al [17] using Pd paint. They reported typical lambda values of 100 in the temperature range 350-450°C, in good agreement with the results of this study.…”

“…The reported Faradaic efficiency values were quite low due to the high operating temperatures (650-750°C) and consequent short lifetime of the promoting species and important part of the non catalytic homogeneous reaction. Another study [17] focused on a lower temperature range (350-450°C) and reported higher average lambda values around of 100 and q values up to 90. Frantzis et al [13] found quite similar faradaic efficiency values typically between 30 and 150.…”