Hydrogenation and H-D exchange of chemisorbed ethylene on Ni(100) under vacuum

Thermal desorption (TDS) and high-resolution electron energy loss (HREELS) spectroscopies have been used to study the reactivity of ethylene with coadsorbed hydrogen on Ni(100) surfaces under vacuum conditions. Hydrogen coadsorption weakens ethylene chemisorption, decreasing the activation barrier and increasing the desorption yield compared to those of the unmodified ethylene adsorption. HD exchange in ethylene takes place to a large extent; up to 20–30% of the molecules go through at least one exchange reaction before desorbing. Ethylene hydrogenation competes with both molecular desorption and HD exchange and is very sensitive to chemisorption geometries. The yields and energetics of all three reactions are greatly influenced by the relative coverages and the order of dosing between ethylene and hydrogen.