Rate and oxygen activity oscillations during hydrogen oxidation on nickel films in a CSTR

Abstract

The catalytic oxidation of hydrogen on polycrystalline nickel films was studied in a CSTR at 510-681°K and atmospheric pressure. The technique of Solid Electrolyte Potentiometry (SEP) was used to monitor the thermodynamic activity of oxygen adsorbed on the catalyst surface. To this end the reaction was studied in an yttria-stabilized zirconia solid electrolyte cell. Both steady state kinetics and potentiometric results indicate formation and reduction of a surface nickel oxide. In a certain range of temperature and gas composition sustained oscillatory phenomena were observed on both the reaction rate and the surface oxygen activity. A dynamic model of six differential equations that takes into account transient changes of the gas phase concentration of H 2, O 2 and H 2O as well as of the surface coverage of adsorbed hydrogen, oxygen and nickel oxide has been developed. The model explains quantitatively the stable steady state kinetic and SEP results. The same model predicts oscillatory behavior and explains qualitatively the observed unsteady state phenomena.