KINETICS OF OH FORMATION ON PT IN H2O/O2 MIXTURES AT HIGH-TEMPERATURES

The formation of OH from adsorbed oxygen and water on a polycrystalline platinum foil at high temperatures (almost-equal-to 1200 K) and at a total pressure of 50 mTorr, has been investigated as a function of H2O/O2 ratio and surface temperature. The maximum in the OH desorption rate occurs at the H2O/O2 ratio 2.3. and is about 7 times weaker than from the H-2 + 1/2O2 reaction. The apparent desorption energy determined from Arrhenius plots of the data varies with the H2O/O2 ratio and deviates from the "true" activation energy for OH desorption, determined in the water formation reaction. The experimental data can be qualitatively understood by kinetic considerations and are quantitatively reproduced by a kinetic model previously developed for the water formation reaction. The latter suggests that H2O --> OH + H dominates over H2O + O --> 2OH in the water decomposition.