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Accueil du site > LPCNO > Séminaires > 2019 > Hydrogen Induced Structure Change of Ruthenium Clusters

Hydrogen Induced Structure Change of Ruthenium Clusters

Date : 14/03/2019 à 14:00

Titre : Hydrogen Induced Structure Change of Ruthenium Clusters

Intervenant : Detlef Schooss

Provenance : Institut für Nanotechnologie, Karlsruhe

Salle : Salle de séminaire - LPCNO

Abstract : Supported ruthenium nanoparticles are the active species in the Kellog Advanced Ammonia Process. Model studies have established that the optimal nanoparticle size range is on the order of a few nm. This has been rationalized in terms of the number density of active areas (B5-sites) for dissociative chemisorption of N2 present on the surface of Ru nanoparticles. We have studied the structures of bare and hydrogenated Ru-clusters RunHm- using trapped ion electron diffraction in combination with density functional theory in a size range of n=14 - 231 with varying hydrogen coverage. While for the bare clusters hexagonal layered or close packed fcc structures were found, hydrogenation changes the structure type of the ruthenium core towards an icosahedral motif. Density functional theory computations reveal the driving force behind this process to be the larger hydrogen adsorption energies for the icosahedral structure type. TIED measurements indicate that the hydrogen induced structure change extends up to  200 ruthenium atoms - a size range which is identical to the onset of catalytic activity. Because icosahedral structures cannot accommodate B5-sites, this mechanism could provide an additional/alternative explanation for the size dependence catalytic activity at small particle sizes.