Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 20: Oberflächenreaktionen I

O 20.8: Talk

Tuesday, March 9, 2004, 13:00–13:15, H45

Influence of Mn and Co on the Properties of Active Sites in Molybdena Based Catalysts; DFT Cluster Model Studies — •Renata Tokarz-Sobieraj and Malgorzata Witko — Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Krakow, Poland

Molybdenum oxide (VI) in combination with other elements such as Bi, V, Co, or Mn forms a large group of materials (molybdates, molybdenum bronzes, heteropolyacids) that are used as catalysts in many reactions of very different types. In the present work the local electronic and geometric structure of the clean and reduced manganese molybdate (MnMoO₄) as well as cobalt molybdate (CoMoO₄) is discussed and compare with pure MoO₃ to examine the influence of the additional atoms (Mn, Co) on chemical properties of active sites. In all studied systems the nucleophilicity of surface oxygen (measured by its charge) scales with the coordination number. Replacement of Mo atom by Mn or Co atoms decreases the charge (nucleophilicity) of oxygen sites. The surface Mn and Co ions form Lewis centers, which are less strong than the Mo ions; in molybdates the presence of Mn and Co atoms increase the acidity of Mo centers. In all studied systems metal-oxygen bonds are characterized by mixed ionic-covalent character, where the Mn/Co-O bonds are more covalent than Mo-O bonds.