The sol-gel process was used to prepare supported vanadium phosphate (VPO) membranes adapted to the mild oxidation of n-butane to maleic anhydride in a membrane reactor. Starting from a vanadium oxoalkoxide, two different sol-gel methods have been investigated: the colloidal route in aqueous media and the polymeric route in organic media. The membrane synthesis as well as the characteristics of the VPO precursors are described on the basis of the fundamental phenomena occurring during the sol-gel process. The VPO precursors and the derived catalysts were characterized through TGA, elemental analysis, LRS, XRD and Nz adsorption-desorption. The polymeric route yielded an attractive hybrid organic-inorganic VPO precursor adapted to the synthesis of infiltrated VPO/alpha-Al2O3 composite membranes stable up to 500 degrees C. N-2 permeation experiments were used to characterize the membranes after n-C4H10 and O-2 heat-treatment cycles. Gravimetric analysis were useful to ;correlate the structural characteristics and permeation behavior of the VPO membranes after n-C4H10 or O-2 treatments. (C) 2000 Elsevier Science B.V. All rights reserved.