Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 86: Heterogeneous catalysis I
O 86.10: Vortrag
Donnerstag, 17. März 2011, 18:45–19:00, WIL B122
Methane activation on palladium (-oxide) — •Anders Hellman1, Adriana Trinchero1, Henrik Grönbeck1, Johan Gustafson2, Edvin Lundgren2, and Jesper Andersen2 — 1Applied Physics and Competence Centre of Catalysis, Chalmers University of technology, Göteborg, Sweden — 2Division of synchrotron radiation research, Lund University, Sweden
The transition state and the activation energy of methane dissociation on several palladium and palladium oxide facets together with known surface oxides phase is investigated by density-functional theory calculations. Depending on the phase of the palladium there is a correlation between the activation energy and the final energy of the CH3+H product. The metal phase of palladium has a low activation energy, with a steep correlation to the final state. The palladium oxide and surface oxide have higher activation energies and a more moderate dependence on the final state. If the palladium oxide and surface oxide is reduced, i.e., a removal of an oxygen atom at the active site, another correlation appears that lie in between the metal and oxide phase.
Given the high activation energy of the two most stable palladium oxides, i.e., PdO(100) and PdO(101), the general belief that palladium oxide is a particularly active methane oxidation catalyst is challenged. Instead, our first-principles results suggest that the high activity of palladium can be explained by the appearances of high surface energy facets of the palladium oxide and/or as the occurrences of reduced palladium oxides as the temperature varies under the experiment.