Münster 1999 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
O: Oberflächenphysik
O 21: Oxide und Isolatoren/Phasenüberg
änge
O 21.1: Vortrag
Mittwoch, 24. März 1999, 14:30–14:45, S10
Formation of Water Species at the V2O5(010) Surface: Quantum Chemical Cluster studies. — •M. Witko1,2, R. Tokarz1,2, K. Hermann2, R. Druzinic2, and R. Grybos1 — 1Institute of Catalysis and Surface Chemistry, ul. Niezapominajek, 30-239 Cracow, Poland — 2Fritz-Haber-Institut, Faradayweg 4-6, 14 195 Berlin, Germany
The efficiency of V2O5-based catalysts in oxidation processes depends on their ability to provide lattice oxygen as the reactant either to adsorb hydrogen abstracted from the organic molecule or to be inserted into the organic species. Cluster model calculations by means of ab initio DFT and semiempirical ZINDO methods were carried out to identify surface oxygen sites which are active in the formation of surface OH and H2O species after H adsorption. The V2O5(010) surface was modeled by a bond saturated V10O31H12 cluster which contains the three structurally inequivalent surface oxygen sites, vanadyl oxygen sites singly coordinated to V, and bridging oxygen sites coordinated to two or three V atoms. The geometries of the surface OH and H2O species were optimized to obtain equilibrium. Hydrogen stabilizes at all sites where strongest binding is found for the vanadyl oxygen centers. The surface OH groups may attract a second hydrogen which results in a surface H2O species. The water species formed at the bridging oxygen sites is bound most weakly and may easily desorb. In contrast, surface H2O at vanadyl oxygen sites is bound quite strongly and may stop the catalytic activity of these centers. Altogether the present results suggest that bridging oxygen sites dominate in the oxidation process.