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O: Oberflächenphysik
O 28: Oxide und Isolatoren (I)
O 28.8: Vortrag
Donnerstag, 30. März 2000, 13:00–13:15, H44
Oxygen Vacancies at the MoO3(010) surface: Cluster Model Studies — •M. Witko1,2, R. Tokarz1,2, and K. Hermann2 — 1Institute of Catalysis, PAS, ul.Niezapominajek, 30-239 Cracow, Poland — 2Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin
MoO3 compounds are functional components of catalysts in a large number of processes to convert hydrocarbon to other chemicals. Each of theses reactions involves several steps (e. g. abstraction of hydrogen, insertion of oxygen) yielding different products, as a function of the local surface geometry, as well as oxygen surface vacancies. The MoO3(010) surface contains differently (singly, doubly, and triply) coordinated oxygen centers which differ in their electronic/catalytic properties. Therefore, to understand a reaction mechanism in detail, one has to find out which of the structurally different surface oxygens is involved in a particular step. In the present study, we model the MoO3(010) surface by an embedded Mo15O56H22 cluster representing two layers of the substrate where the local electronic structure is determined within the density functional theory scheme. To identify the chemical reactivity of each type of surface oxygen the adsorption of H or two H atoms (leading to surface OH or H2O species) at respective oxygen sites is studied. Hydrogen stabilizes at all structurally different oxygen sites and adsorption leads to elongation of respective Mo-O bond distances as well as to reduction of the nearby metal centers. Further, details of surface oxygen vacancies created by O/OH/H2O removal are reported. The results suggest that the presence of hydrogen at the oxide surface facilitates oxygen removal where the effect is larger for H2O than for OH.