Influence of MgO-modified SBA-15 on the structure and catalytic activity of supported vanadium oxide catalysts

Vanadium oxides on an alkaline, high-surface-area MgO/SBA-15 support are introduced as a model system for investigating structure–activity correlations in selective oxidation reactions. The supported vanadium oxide catalysts were investigated by X-ray diffraction, N2 physisorption, X-ray absorption spectroscopy, and diffuse reflectance UV–vis spectroscopy. The vanadium oxide species consisted of tetrahedral units, while the oligomerization degree depended on catalyst loading and vanadium oxide dispersion. Low-oligomeric [VO4] tetrahedra could be stabilized at comparably high coverage due to the alkaline surface of the oxide support. The structure was compared to higher-oligomeric vanadium oxide species present on acidic supports such as SBA-15. Catalytic performance of the oxide catalysts in selective propene oxidation was investigated by gas chromatography. Acrolein turnover frequency as a function of surface coverage exhibited volcano-type behavior. At optimal surface coverage, the catalyst structure consisted mainly of dimeric [V2O7] units.