Incorporation of promoter elements into the crystal lattice of (VO)₂P₂O₇ and its promotion effects on the oxidation of n-butane to maleic anhydride

A new preparation method to introduce promoter ions into the (VO₂)P₂O₇crystal lattice was developed. A precipitate was obtained by the addition of a small amount of water to a blue isobutanol refluxing solution which contained reduced and dissolved V₂O₅ and the acetylacetonate of a promoter element. The catalyst which was prepared by the calcination of this precipitate had the same composition as that of the starting solution. Observation of the catalyst using energy-dispersive X-ray and wavelength-dispersive X-ray showed no evidence of localization of the added promoter element. The ESCA (electron spectroscopy for chemical analysis) depth profile of the component elements suggested a homogeneity between the surface and the bulk of the catalyst. There is a linear relationship between the activity of the catalysts for MA formation and the position of the VO IR absorption bands of the catalysts containing promoter elements. The active sites of the catalysts and the activity of the surface VO are discussed.