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 catalyst 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 that the open-circuit (unpromoted) catalytic rate and at least a factor of 5000 higher than the rate of O2- supply through the mixed conducting TiO2 support. The latter is and remains catalytically inert during electrical bias. This electrochemically induced Schwab effect of the second kind has all the same qualitative features with the effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA effect) when using pure O2- conductors. Work function measurements and X-ray photoelectron spectroscopic (XPS) investigation of the Pt catalyst surface under UHV conditions has also provided evidence consistent with the electrochemically controlled promoting oxide ion backspillover mechanism which is operative with NEMCA when using pure O2- conductors. Under reaction conditions in atmospheric pressure or oxidizing environments in UHV the TiO2 support exhibits mixed electronic (n-type)-ionic conductivity and thus the catalyst work function and catalytic activity can be controlled by the applied potential. In reducing environments the electronic conductivity of TiO2 dominates and the catalyst work function remains constant upon application of potential. (C) 1996 Academic Press, Inc.