Reaction of CO with H2 on Ru, Ru–Fe and Fe films

Abstract

Ru, Ru–Fe and Fe films have been prepared in u.h.v. conditions. In temperature-programmed desorption experiments (t.p.d.) a reasonable desorption rate for both H₂ and CO at ca. 550 K (the reaction temperature for the CO + H₂ reaction) was observed only for Ru films, especially when the gases were adsorbed at 673 K and cooled to 300 K in H₂ and CO, respectively. CO₂ formation was observed in t.p.d. only, when large amounts of H₂O were present.

CH₄ was the only product in the CO + H₂ reaction at 10 Pa pressure on Ru. On Ru film surface carbon deposited by the dissociation of CH₄ or CO could readily be hydrogenated to CH₄. A mechanism for the CO + H₂ reaction is proposed in which chemisorbed CO having a very weak bond between the carbon and oxygen atoms reacts with hydrogen, resulting in surface carbon and H₂O. CH₄ forms only in the next hydrogenation step. Iron and ruthenium–iron films, the latter being enriched in iron, proved to be completely inactive in this reaction. A possible explanation is given.