Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 18: Adsorption an Oberflächen I

O 18.5: Talk

Tuesday, March 9, 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 Hermann² — ¹Institute 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 E_B(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.