Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 27: Poster Session I (Methods: Scanning probe techniques; Methods: Atomic and electronic structure; Methods: Molecular simulations and statistical mechanics; Oxides and Insulators: Clean surfaces; Oxides and Insulators: Adsorption; Oxides and Insulators: Epitaxy and growth; Semiconductor substrates: Clean surfaces; Semiconductor substrates: Epitaxy and growth; Semiconductor substrates: Adsorption; Nano- optics of metallic and semiconducting nanostructures; Electronic structure; Methods: Electronic structure theory; Methods: other (experimental); Methods: other (theory); Solutions on surfaces; Epitaxial Graphene; Surface oder interface magnetism; Phase transitions; Time-resolved spectroscopies)
O 27.37: Poster
Dienstag, 24. März 2009, 18:30–21:00, P2
Acrolein decomposition on cerium-oxide model-catalysts: Correlation between structure and reactivity — •Jan Markus Essen, Conrad Becker, and Klaus Wandelt — Institute of Physical and Theoretical Chemistry, University of Bonn, Wegelerstrasse 12, D-53115 Bonn, Germany
The mechanism of reversible oxygen transfer by cerium oxide based catalysts is still quite unclear. Depending on order, oxygen vacancies and the presence of noble metals oxygen exchange with the oxide surface respectively oxidation of adsorbed organic molecules takes place in two temperature regimes, at about 600 K and at about 950 K. While on well ordered ceria on Pt(111) acrolein desorbs completely intact, annealing to 1000 K leads to an oxygen vacancy related coupling of acrolein on the surface. Electron bombardment of ceria on Pt(111) at 300 K results in hydroxylated surfaces with adsorbed CO2 and H2O. Acrolein TPD shows no defect formation. Disordered reduced oxides are generated by oxygen adsorption on 2 ML Ce/Pt(111). Acrolein decomposition here proceeds via C1-O bond cleavage at 600 K. The remaining propylidine decomposes at 950 K in combination with CO/CO2 desorption. Finally, Pd deposited on ceria on Pt(111) shows a carbon removal by recombinant CO desorption at about 600 K. The reaction with the surface oxygen at 600 K is suggested to be caused by an enhanced oxygen diffusion starting at this temperature, while the oxidation at 950 K is assumed to result from desorbing oxygen forming O2 vacancies.