Molybdenum oxide supported on nanostructured MgO: Influence of the alkaline support properties on MoO_x structure and catalytic behavior in selective oxidation

摘要

Local structure and catalytic activity of molybdenum oxide supported on alkaline, nanostructured support materials were investigated. The structure of the surface oxide catalysts was significantly affected by the properties of the support. The support material was prepared via two different routes. A direct MgO synthesis approach was compared to SBA-15 coated with magnesium oxide. The structure of the support materials was investigated by XRD and N2 physisorption. Both materials exhibited a high specific surface area with a narrow pore size distribution. The MgO-coated SBA-15 (MgO/SBA-15) exhibited a similar alkaline character as pure nanostructured MgO (nano-MgO) but was more stable under catalytic conditions. The highly dispersed molybdenum species on the support was characterized by XRD, XAS and DR-UV-Vis spectroscopy. The catalytic activity for selective oxidation of propene was investigated by gas chromatography. A considerably different species was present on the alkaline support, compared to more acidic support materials like SBA-15. The structure of the supported molybdenum oxide consisted of predominantly isolated [MoO4] tetrahedra and was largely independent from Mo loadings. The supported catalysts with isolated [MoO4] tetrahedra exhibited only poor catalytic activity compared to the higher polymerized Mo species supported on silica SBA-15.