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O: Oberflächenphysik

O 24: Adsorption III

O 24.7: Vortrag

Dienstag, 28. März 2006, 17:15–17:30, TRE Phys

SFG and TDS studies of CO adsorption on Pd nanoparticles supported by Nb2O5 and Fe3O4 thin films — •Frank Höbel, Atula Bandara, Günther Rupprechter, and Hans-Joachim Freund — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

CO adsorption on Nb2O5- and Fe3O4-supported Pd nanoparticles was studied by sum frequency generation (SFG) vibrational spectroscopy from ultrahigh vacuum (UHV) to 100 mbar, and by thermal desorption spectroscopy (TDS) under UHV. Differences between the Pd-Nb2O5/Cu3Au(100) and Pd-Fe3O4/Pt(111) model catalysts will be discussed. Heating the Pd-Nb2O5 system to 300 K resulted in an irreversible decrease in CO chemisorption associated with a phase shift in the SFG spectra. This indicates a modification of the electronic structure of the particles and a formation of mixed Pd-NbOx sites. Pd-Fe3O4 model catalyst, on the other hand, were rather stable up to ~600 K. For 10 nm Pd particles no pronounced changes were observed by SFG and TDS spectra, both methods revealing well-ordered particle facets. However, smaller Pd particles (~ 6 nm) showed different CO bands in SFG, pointing to rougher surfaces, and also phase changes occurred during annealing. Possible surface modifications during annealing (TDS) will be discussed