The Structure Determination of Ru₃(CO)₁₂ Catalysts Supported on Inorganic Oxides by Means of EXAFS

Abstract

The structures of the Ru catalysts derived from Ru₃(CO)₁₂ supported on the various oxides such as MgO, K-doped Al₂O₃, Al₂O₃, TiO₂, Sio₂, V₂O₅, and MnO₂ were studied by means of EXAFS (extended X-ray absorption fine structure). The surface Ru structures are illustrated in Fig.9. The structures obtained by supporting Ru₃(CO)₁₂ onto the oxides depended on the acidity and basicity of supports. [HRu₃(CO)₁₁]^- was formed on the basic supports like MgO and K-doped Al₂O₃, whereas [Ru₃(CO)₁₀ (H)(OA )] was created on the amphoteric support like Al₂O₃. On the more acidic supports like TiO₂, SiO₂ and V₂O_5, Ru₃(CO)₁₂ was physisorbed. The structures formed after the thermal treatments and H₂ reduction of the incipient surface Ru species can be explained in terms of the electronegativity of metal ions in the support oxides. On MgO and Al₂O₃ in which the electronegativities of the metal ions are relatively small, the chemical bonds between the surport oxygen and Ru atoms were formed after the thermal decomposition and H2 reduction. On TiO₂, SiO₂ and V₂O₅ in which the metal ions have large electronegativities, the Ru metal particles with no Ru-O bonding were observed. In the case of MnO₂, the oxidation of the Ru cluster by th e support was observed in addition to the metal-support interaction mentioned above.