Finite size effects on supported Pd nanoparticles: Interaction of hydrogen with CO and C2H4

Pd-hydride formation proceeds predominantly via minority sites on Pd nanoparticles (defects and (1 0 0) facets). Finite size effects govern the surface chemistry, e.g. “explosive” hydrogen desorption in the presence of a CO overlayer originates from the confinement of dissolved hydrogen within the limited nanoparticle volume. In situ surface vibrational spectra, acquired during CO hydrogenation under technical conditions, suggest surface roughening or a partly disordered CO adsorbate phase that only occur at elevated pressure. The presence of Pd-hydride phases yielded a very high activity for C2H4 hydrogenation on the Pd nanoparticles which may again be related to the hydrogen confinement effect.