title: Tuning the surface chemistry of Pd by atomic C and H: a microscopic picture.
abstract: Palladium is crucial for industry-related applications such as heterogeneous catalysis, energy production, and hydrogen technologies. In many processes, atomic H and C species are proposed to be present in the surface/near-surface area of Pd, thus noticeably affecting its chemical activity. This study provides a detail and unified view on the interactions of the H and C species with Pd nanoparticles (NPs), which is indispensable for insight into their catalytic properties. Density functional calculations of the interplay of C and H atoms at various concentrations and sites on suitable Pd NPs have been performed, accompanied by catalysis-relevant experiments on oxide-supported bare and C-modified Pd NPs. It is shown that on a Pd(79) NP a subsurface C atom destabilizes nearby atoms H at low coverage. Our experiments confirm that H atoms bind more weakly on C-containing Pd NPs than on C-free NPs. Various factors related to the presence of both H and C atoms on a Pd(79) surface, which may influence the penetration of H atoms from the surface into the subsurface area, have been investigated. Carbon atoms facilitate the subsurface penetration of atomic H both thermodynamically and kinetically when the surface is densely covered by H atoms. Moreover, subsurface H atoms are also energetically favored, even in the absence of C atoms, when several facets of the NP are covered by H atoms.
authors.affiliation: Departament de Química Física and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona c/Martí i Franquès, 1, 08028 Barcelona, Spain.
authors.forename: Hristiyan A
authors.initials: HA
authors.lastname: Aleksandrov
authors.forename: Francesc
authors.initials: F
authors.lastname: Viñes
authors.forename: Wiebke
authors.initials: W
authors.lastname: Ludwig
authors.forename: Swetlana
authors.initials: S
authors.lastname: Schauermann
authors.forename: Konstantin M
authors.initials: KM
authors.lastname: Neyman