Thesis (D.Eng.)--Chulalongkorn University, 2012

The electrochemical promotion of ethylene and propane oxidation has been investigated in comparison upon different catalyst-electrodes. Depending on experimental conditions (temperature and gas composition), in the case of the electrochemical promotion of C2H4 oxidation over Pt/YSZ, this is the first time to demonstrate three out of four promotion behaviours, i.e. here for electrophobic, electrophilic, and volcano types by the use of single catalytic reaction. It was found that under mildly oxidizing conditions the reaction exhibits an electrophobic behavior, i.e. rate increase by anodic polarization, while it shifts to electrophilic, i.e. rate increase by cathodic polarization, under near stoichiometric feed conditions. The different metal catalyst-electrodes, i.e. Pd, Ru, Ir, and Cu were tested on deep propane oxidation under lean burn condition and at temperature range of 250-450oC. All of these catalyst-electrodes exhibit electrophobic behavior, where the rate increases during anodic polarization and slightly decreases with negative polarization. The increase in the catalytic rate, Δr, is reached to the maximum ρ values of 3, however, it is significantly higher than the rate of ion transport, I/2F, Λ, taking values up to 250 for Pd, 125 for Ir, and 15 for Ru catalyst-electrode under anodic polarization. Fast catalyst deactivation is observed due to increased particle size as observed by SEM and XRD. The better catalytic performance of Pd with MnxOy in comparison on Pd deposited on YSZ is observed and confirmed by the kinetic studies exhibiting the shift of rate maximum at higher oxygen partial pressure. Propane oxidation can be reversibly enhanced by the Pd metallic phase via the application of current or potential up to 1000, whereas the interlayer of MnxOy hinders the electrochemical promotion of propane oxidation in excess of oxygen.