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O: Fachverband Oberflächenphysik

O 93: Heterogeneous Catalysis: Experiment

O 93.1: Hauptvortrag

Donnerstag, 23. März 2017, 15:00–15:30, TRE Phy

Oxygen and Oxide Cluster Functionalized Graphene for Model Catalytic Studies — •Zdenek Dohnalek — Pacific Northwest National Laboratory, Richland, WA, USA

Well-defined, monodispersed catalysts supported on oxidized carbon nanotubes and nanosheets are a promising class of new materials for heterogeneous catalysis. We have chosen graphene (Gr) supported on Ru(0001) as a surface science model and employed scanning tunneling microscopy to investigate its functionalization with oxygen atoms (AOs) and ceria and titania nanoclusters. On Ru(0001), Gr forms a Moiré structure with a periodicity of 3 nm with three distinct regions: C ring atop Ru, on HCP and FCC. At room temperature, AOs are found preferentially within the FCC regions. At 400 - 500 K, the AOs move primarily within the FCC regions or away from the metastable HCP regions. The high-resolution time-lapse data is used to assign the AO adsorption configuration to the on-top terminally-bound groups rather than the expected bridge-bonded epoxy species. For ceria and titania nanoclusters we find that they are anchored at the intrinsic defects in Gr. The thermal evolution of the cluster size distribution suggests that the sintering proceeds via diffusion and aggregation of entire clusters. To follow the cluster redox properties we examined their oxygen storage and release in an oxygen atmosphere at elevated temperature (550 - 700 K). Under oxidizing conditions, oxygen intercalation under the Gr layer is observed for ceria but not titania. Time-dependent studies demonstrate that the intercalation starts in the vicinity of the ceria clusters and extends until a completely intercalated layer is observed.