Structure and catalysis of vanadium oxide overlayers on oxide supports Original Research Article

The structure and catalysis of supported vanadium oxides reported in the literature are reviewed first. Then our study on the vanadium oxide overlayers prepared by chemical vapor deposition (CVD) of VO(OC2H5)3 and impregnation (Imp) on SiO2, Al2O3 and MgO is described. The structures were characterized by XRD, XPS, EXAFS and Raman spectroscopy. Loading levels varied from 1.9 to 16.9 wt%. The vanadium oxides on SiO2 prepared by CVD were mostly in the form of thin layers. On the other hand, the isolated species (<5 wt%) and the crystallites (> 5 wt%) were formed on SiO2 by an impregnation method. Thin layers were present on Al2O3 regardless of the preparation method. On MgO, vanadium existed as Mg3V2O8 phase. Thin overlayers and the crystallites were active for oxidative dehydrogenation of alcohols, the activity of the former being higher. The isolated species was inactive, indicating that the sites having V—O—V bonds are necessary for this reaction.