Hydrogenation of small hydrocarbons on MgO supported Pd nanoparticles: The A-E-model expanded

The hydrogenation of ethylene and acetylene was studied on a Pd_n/MgO/Mo(100) model system containing palladium particles with a narrow size distribution around Pd₂₆ (Pd₂₀ to Pd₃₅). Reactivity measurements were carried out in an ultrahigh vacuum chamber under isothermal conditions in the presence of deuterium. The catalyst system can readily hydrogenate both of these small molecules, and for acetylene, an alternative reaction network exists, in which it is trimerized to benzene. Distinct deactivation behavior was found for the two molecules and ascribed to different adsorption sites formed and influenced by the carbonaceous overlayer formed during the course of the reaction. These findings extend the A-E-model by Borodziński and Gołȩbiowski to extremely small particles and low partial pressures and show that it is possible to study realistic catalytic sites under highly defined conditions.