Kinetics, limit cycles, and mechanism of the ethylene oxidation on platinum

Abstract

The oxidation of ethylene on polycrystalline Pt films was studied in a CSTR at atmospheric pressure and temperatures between 200 and 400 °C. The new technique of solid electrolyte potentiometry (SEP) was used to monitor the activity of oxygen on the metal catalyst. To this end the platinum film catalyst also served as one of the electrodes of a solid-electrolyte oxygen concentration cell and the open-circuit emf of the cell was monitored during reaction. It was found that the steady-state surface oxygen activity a 0 satisfies the equation a 0 = K s P O 2 P ET , where K s depends on temperature only. The reaction rate is first order in ethylene and adsorbed oxygen. Over a certain range of temperature and gas-phase composition both the surface oxygen activity and the reaction rate exhibit self-sustained oscillations. Limit cycles appear only over a well-defined range of surface oxygen activity a 0 values. The oscillations can be explained in terms of the stability of a surface platinum oxide. The reaction mechanism is discussed in light of these observations.