Interactions between Chemisorbed Species: H2 and CO on (100) Tungsten

Abstract

The interaction of CO with chemisorbed β‐hydrogen on the (100) plane of tungsten has been investigated using flash desorption and work function methods. CO efficiently displaces chemisorbed hydrogen from tungsten at temperatures near 300°K. This is a result of the CO‐induced lowering of the activation energy for H₂ desorption, with the CO chemisorbing initially on sites other than those occupied by hydrogen. At ∼ 100°K, little CO‐induced displacement of chemisorbed hydrogen occurs, and the production of three weakly bound hydrogen states (designated ν‐hydrogen) is observed. Each $\nu$ state exhibits a range of desorption energies. During the CO‐induced surface conversion of β‐hydrogen to ν‐hydrogen, a decrease in work function is observed. All of this behavior is indicative of a major interaction between adsorbed CO and adsorbed hydrogen. A weakly‐bound molecular H₂ state (δ‐hydrogen) may be populated by adsorption of H₂ on top of partial CO layers on W(100) at ∼ 100°K. The sites adsorbing this molecular state of hydrogen are related to the presence of β‐CO species, and are probably the same sites which could adsorb α‐CO at higher CO coverages. In thermal desorption, the liberation of two discrete hydrogen binding states ${\mathrm{(\beta }}_1\mathrm{and}{\beta }_2)$ from pure hydrogen layers on W(100) is probably a result of coverage‐dependent interactions between identical adsorbed H‐atom species. No chemical differences are observed in this work between hydrogen species responsible for the two β‐hydrogen binding states. No catalytic production of H₂CO, HCO, CH₄, or C₂H₆ was observed in coadsorption of hydrogen and CO on W(100).