Adsorption-desorption kinetics of H2 from clean and sulfur covered Ru(001)

The adsorption and desorption kinetics of hydrogen from clean and partially sulfided surfaces of the (001) face of ruthenium were studied. Adsorption is dissociative and can be described by (1-theta)2 kinetics. Desorption rate isothermal analysis of flash desorption spectra of hydrogen from the clean surface show that the desorption energy for hydrogen decreases linearly with increasing H2 coverage. The low coverage value of the desorption energy is 26 kcal/mole, decreasing to approximately 11 kcal/mole at a coverage thetasub(H) approximately 0.8. The pre-exponential factor varies in sympathy with the desorption energy and thus the apparent second-order rate constant demonstrates a compensation effect. No hydrogen could adsorb on the first ordered overlayer of sulfur - the Ru(001)-(2x2)S. The LEED pattern was preserved which indicated that hydrogen does not displace sulfur from this surface. The effect of increasing amounts of sulfur on hydrogen adsorption is to rapidly suppress the saturation amount of hydrogen that can be adsorbed. (Auth.)