Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 64: Oxides and Interfaces: Adsorption II
O 64.4: Talk
Wednesday, March 9, 2016, 15:45–16:00, H6
Exploring Pd adsorption, diffusion, permeation, and nucleation on bilayer SiO2/Ru as a function of hydroxylation and precursor environment; from UHV to catalyst preparation — Sascha Pomp1,2, William Kaden2, •Martin Sterrer1,2, and Hans-Joachim Freund2 — 1Institute of Physics, University of Graz, Graz, Austria — 2Department of Chemical Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
The hydroxylation-dependent permeability of bilayer SiO2 supported on Ru(0001) was investigated by XPS and TDS studies. For this, the thermal behavior of Pd evaporated at 100 K, which results in surface and sub-surface binding arrangements, was examined relative to the extent of pre-hydroxylation. Samples containing only defect-mediated hydroxyls showed no effect on Pd diffusion through the film. If, instead, the concentration of strongly bound hydroxyl groups and associated weakly bound water molecules was enriched by an electron-assisted hydroxylation procedure, the probability for Pd diffusion through the film is decreased via pore-blocking. Above room temperature, all samples showed similar behavior, reflective of particle nucleation above the film. When depositing Pd onto the same SiO2/Ru model-support via adsorption of [Pd(NH3)4]Cl2 from alkaline (pH 12) precursor solution, we observe notably different adsorption and nucleation mechanisms. The Pd adsorption complexes follow established decomposition pathways to produce model-catalyst systems compatible with those created exclusively within UHV despite lacking the ability to penetrate the film due to the increased size of the initial Pd precursor groups.