NON-FARADAIC ELECTROCHEMICAL MODIFICATION OF CATALYTIC ACTIVITY .9. ETHYLENE OXIDATION ON PT DEPOSITED ON TIO2

The catalytic activity of Pt for the oxidation of ethylene to CO2 can be markedly and reversibly affected by interfacing polycrystalline Pt films with TiO2 and applying currents or potentials between the cataly st film and a Au counter electrode at temperatures near 500 degrees C. The increase in the rate of C2H4 oxidation is up to 20 times higher t hat the open-circuit (unpromoted) catalytic rate and at least a factor of 5000 higher than the rate of O2- supply through the mixed conducti ng TiO2 support. The latter is and remains catalytically inert during electrical bias. This electrochemically induced Schwab effect of the s econd kind has all the same qualitative features with the effect of no n-Faradaic electrochemical modification of catalytic activity (NEMCA e ffect) when using pure O2- conductors. Work function measurements and X-ray photoelectron spectroscopic (XPS) investigation of the Pt cataly st surface under UHV conditions has also provided evidence consistent with the electrochemically controlled promoting oxide ion backspillove r mechanism which is operative with NEMCA when using pure O2- conducto rs. Under reaction conditions in atmospheric pressure or oxidizing env ironments in UHV the TiO2 support exhibits mixed electronic (n-type)-i onic conductivity and thus the catalyst work function and catalytic ac tivity can be controlled by the applied potential. In reducing environ ments the electronic conductivity of TiO2 dominates and the catalyst w ork function remains constant upon application of potential. (C) 1996 Academic Press, Inc.