Adsorption of oxygen on a Cu(110)Ni surface alloy and its reaction with hydrogen and carbon monoxide

Abstract

Ellipsometry, AES and LEED have been used to study the interaction of O 2 with a Cu(110)Ni surface alloy and the reaction of H 2 and CO with adsorbed oxygen. The surface alloys were prepared by dissociation of nickel carbony1 on a clean Cu(110) surface. The rate of chemisorption of oxygen on a freshly prepared Cu(110)Ni (1°) surface is independent of the crystal temperature and can be described by a precursor state model. The initial sticking probability is ∼0.07 and no saturation is observed at θ=0.5. For θ o > 0.5 the reaction probability of CO with adsorbed oxygen first increases and then decreases: its order of magnitude is ∼10 −5 and the apparent activation energy is ∼ 6.5 kcal/mole. The reaction rate of hydrogen with preadsorbed oxygen is more or less independent of the oxygen coverage at crystal temperatures above 220°C and θ O < 0.5. The reaction rate is limited by the dissociation of hydrogen. At lower crystal temperatures the reaction rate is no longer proportional to the hydrogen pressure and decreases with decreasing oxygen coverage. The reaction of hydroxyl groups at ‘nickel like’ sites appears to be the rate-determining step.