Effect of group 13 compounds and bulky organic oxygenates as structural promoters for the selective oxidation of n-butane with vanadium phosphorus oxide catalysts

Abstract

A detailed study of n-butane oxidation over vanadium phosphate catalysts derived from in situ activation of VOHPO₄·0.5H₂O modified with group 13 compounds or 2-norbonanemethanol is described and discussed. Two methods of preparation of VOHPO₄·0.5H₂O were studied: (a) the VPO method, in which V₂O₅ is reacted with H₃PO₄ in isobutanol, and (b) the VPD method, in which VOPO₄·2H₂O is reacted with isobutanol. Group 13 additives (B, Al, Ga, In) were found to change the morphology of the VPO catalyst precursor from platelet-like to the rosette morphology usually associated with the VPD type of preparation. Although all act as structural modifiers, the In- and Ga-doped materials give improved catalyst performance for the synthesis of maleic anhydride from the selective oxidation of n-butane. The Al, Ga and In additives were added as acetylacetonates and it was found that addition of 1% acetylacetonate also enhances the catalyst performance, but does not act as a structural promoter. In view of this, the addition of 2-adamantanol and 2-norbonanemethanol was investigated for the VPD-type preparation method. The addition of 2-norbonanemethanol was found to enhance the catalyst surface area of the activated catalyst, but the catalyst performance, with respect to both n-butane conversion and maleic anhydride selectivity, was not improved and this is considered to be due to the alcohol being strongly adsorbed on the catalyst surface.