The effects of a surface S coverage upon the surface diffusion of H on the (001) planes of Ru were studied using laser-induced thermal desorption techniques. Measurements which were performed at 270 or 300K revealed that the surface mobility of H decreased rapidly as a function of increasing S coverage. At 300K, the H surface diffusion coefficient decreased by a factor of about 30, from 8.5 x 10-7 to less than 3 x 10-8cm2/s, as the S coverage increased from 0 to 0.25 of a monolayer. The reduction in H surface mobility versus S coverage was compared with the predictions of a site-blocking model. In order to reproduce the rapid decrease in H surface mobility as a function of S coverage, the site-blocking model indicated that each S adatom would have to block ten H adsorption sites. The effect of S upon H surface mobility was attributed to both steric and long-range electronic effects. A reduced surface mobility with increasing S coverage was suggested to explain the effect of S as a poisoner of catalytic reactions.

J.L.Brand, A.A.Deckert, S.M.George: Surface Science, 1988, 194[3], 457-74