Non-Faradaic Electrochemical Modification of Catalytic Activity: 9. Ethylene Oxidation on Pt Deposited on TiO2

Abstract

The catalytic activity of Pt for the oxidation of ethylene toCO2can be markedly and reversibly affected by interfacingpolycrystalline Pt films with TiO2and applying currents orpotentials between the catalyst film and a Au counter electrodeat temperatures near 500°C. The increase in the rate of C2H4oxidation is up to 20 times higher that the open-circuit(unpromoted) catalytic rate and at least a factor of 5000 higherthan the rate of O2−supply through the mixed conducting TiO2support. The latter is and remains catalytically inert duringelectrical bias. This electrochemically induced Schwab effect ofthe second kind has all the same qualitative features with theeffect of non-Faradaic electrochemical modification of catalyticactivity (NEMCA effect) when using pure O2−conductors. Workfunction measurements and X-ray photoelectron spectroscopic(XPS) investigation of the Pt catalyst surface under UHVconditions has also provided evidence consistent with theelectrochemically controlled promoting oxide ion backspillovermechanism which is operative with NEMCA when using pure O2−conductors. Under reaction conditions in atmospheric pressure oroxidizing environments in UHV the TiO2support exhibits mixedelectronic (n-type)-ionic conductivity and thus the catalystwork function and catalytic activity can be controlled by theapplied potential. In reducing environments the electronicconductivity of TiO2dominates and the catalyst work functionremains constant upon application of potential.