HYDROGEN DISPLACEMENT OF CHEMISORBED CO FROM THE Ni(100) SURFACE

We report the first observation of hydrogen induced displacement of chemisorbed CO from the Ni(100) surface. This displacement is unexpected since the heat of adsorption for CO is 126 kJ/mole, about 30 kJ/mole larger than the 96 kJ/mole heat of adsorption for hydrogen, Rates of displacement were measured by Fluorescence Yield Near Edge Spectroscopy (FYNES) and Temperature Programmed Desorption (TPD). Excellent agreement is observed between both methods. Hydrogen pressures in the 10~(-4) to 10~(-1) Torr range cause displacement of chemisorbed CO in the 270 to 330 K temperature range in a matter of minutes. The displacement reaction is clearly positive order in CO coverage. The CO coverage data suggested two first order reaction regions with a decrease in rate with decreasing coverage. Displacement is about half order in hydrogen pressure. The activation energy for the high coverage displacement rate is approximately 29±4 kJ/mole while the activation energy for the low coverage displacement rate about 46