Abstract
Application of an electric potential to Pt–Ag/YSZ catalysts in a C2H4+O2 atmosphere can lead to a significant electrochemical promotion of the catalytic reaction. It is shown that the promotion effect is due to the partial removal of a carbonaceous layer, which poisons the catalytic reaction by electrochemically induced spillover oxygen. [Display omitted]
► 5–6 Layers thick carbonaceous films form on Pt+Ag/YSZ catalysts in catalytic ethylene oxidation under conditions of ethylene being in excess. ► Electrochemical promotion only under conditions at high p(C2H4) when carbonaceous film is present. ► Electrochemical promotion=partial reactive removal of inhibitory carbonaceous layer by electrochemically induced oxygen spillover. ► Reaction non-Faradaic due to ignition effect.
The electrochemical promotion of the C2H4+O2 reaction over a bimetallic Pt/Ag catalyst (Pt:Ag ratio≈1.5) interfaced to yttrium stabilized zirconia (YSZ) has been studied at 0.25mbar and T=650K using X-ray photoelectron spectroscopy as in situ method. Applying a positive potential of 2V causes a relative rate increase in the CO2 production up to 120%; the electrocatalytic promotion effect is non-Faradaic (Λ≈2). An electrochemical promotion is found to occur only at high enough p(C2H4) when a carbonaceous CHx layers builds up inhibiting O2 adsorption. The CHx film is estimated to be about 5–6 layers thick. Only at low p(C2H4), the application of an electric potential causes a decrease in the carbon signal associated with a growth of the O1s signal at 529.3eV. The latter species can be assigned to an electrochemically generated oxygen spillover species at Ag sites.