Effect of support nature on WO 3/SiO 2 structure and butene-1 metathesis

Abstract

Two series of silica-supported tungsten oxide catalysts were prepared by impregnation of ammonium metatungstate aqueous solution on two silica supports with different specific surface areas, followed by calcination in air at high temperature. The prepared catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption and NH 3-TPD. Their catalytic performances in butene-1 metathesis reaction were also investigated. The results revealed that the interaction of tungsten oxide with silica was weaker and that tungsten oxide selectively dispersed on the surface of support with a dispersion capacity of 0.5 W 6+ nm −2. The states of tungsten oxide species formed on the catalyst were dependent on the loading amount of tungsten oxide and on the nature of supports. When the loading amount of tungsten oxide was lower than the dispersion capacity, tungsten oxide species were mainly in the tetrahedrally coordinated states. With the increase of loading amount, the surplus tungsten oxide assembled to form the distorted octahedrally coordinated species on the surface of catalyst. NH 3-TPD results suggested that loading of tungsten oxide on silica should introduce new acid sites on the centers of the metal. As for the reaction of butene-1, the catalytic activity of butene metathesis and that of double bond isomerization over WO 3/SiO 2 were related to the states of tungsten oxide species and to the acid nature of the catalyst, respectively. Tetrahedrally coordinated tungsten oxide species were suggested to be the active centers for metathesis, while acid sites on surface of catalyst should be active centers for double bond isomerization of butene-1.