The adsorption of VO(acac)(2) on a mesoporous silica support by liquid phase and gas phase modification to prepare supported vanadium oxide catalysts

Supported vanadium oxide catalysts are prepared by adsorption and subsequen t calcination of the vanadyl acetylacetonate complex on silica by liquid ph ase and gas phase modification. The influence of the pretreatment temperatu re and the effect of the solvent in the liquid phase are discussed. Two typ es of gas phase deposition processes are used: flow-type reactions and vacu um deposition. The bonding mechanism, the influence of pretreatment tempera ture of the support and the influence of the reaction temperature are inves tigated by FTIR, XRD, TGA and chemical analysis. After calcination the obta ined vanadium oxide layer is characterized by XRD and UV-Vis diffuse reflec tance spectroscopy. The gas phase modification enables the creation of well dispersed supported VOx catalysts. Loadings up to 1.4 mmol g(-1) (7 wt% V) without the formation of a crystalline fraction can be achieved. The selec tive oxidation of methanol to formaldehyde is used as a probe reaction to a ssess the catalytic activity and selectivity of the catalysts. It is shown that not the concentration of vanadium species, but their surface configura tion is the determining factor in catalytic reactions.