The nature of chemisorbed hydroxyl radicals

The energetics of hydroxyl adsorption on Pt, Pd, Rh and Ni have been investigated using the bond order conservation-Morse potential approach (BOC-MP). The heat of adsorption of hydroxyl (QOH) was calculated both under high oxygen coverage and oxygen depleted conditions. Adsorbate-adsorbate interactions must be taken into account in order to explain the observed variation of activation energies for OH desorption reported in the literature for each metal and under different experimental conditions. High oxygen coverages lower the heat of hydroxyl adsorption, while at low oxygen coverages island formation between hydroxyls and hydrogen bonding explain the increase in the heat of adsorption of hydroxyl radicals. The calculated heats of adsorption for the different conditions are in quantitative agreement with experimental results.