Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 18: Adsorption an Oberflächen I

O 18.5: Vortrag

Dienstag, 9. März 2004, 12:15–12:30, H38

Re-oxidation of MoO3 and V2O5 systems: Cluster DFT calculations. — •Malgorzata Witko1, Renata Tokarz-Sobieraj1, Robert Grybos1, and Klaus Hermann21Institute of Catalysis and Surface Chemistry, PAS, ul. Niezapominajek 8, 30-239 Krakow, Poland — 2Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin, Germany

Vanadia and molybdena based systems represent important classes of materials due to their role in technology, catalysis and environmental protection. The goal of the present theoretical research is to examine re-oxidation of V2O5(010) and MoO3(010) surfaces reduced in processes where surface oxygen vacancies are created. All electronic and energetic parameters are obtained by the DFT method using embedded clusters V10O30H12 and Mo15O56H22 clusters as surface models. It is shown that re-oxidation proceeding via O2 adsorption is a very localized process. Oxygen adsorbs at any surface vacancy with binding energies EB(O2) depending on the specific vacancy site (O(1-3)) where the calculations yield an energetic order O(1) < O(2) < O(3) for MoO3 and O(2) < O(1) < O(3) for V2O5. Molecular oxygen becomes adsorbed at the surface and can replace the surface O occupying a specific lattice site with almost no change in the electron distribution of its vicinity. Thus, the reduced oxide surface is able to incorporate large amounts of (weakly bound) oxygen species. The activated oxygen molecule can undergo dissociation yielding reactive products.

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