Synthesis and characterisation of a vanadium-based 'chemical valve' membrane

Abstract

In this work, the reversible red/ox properties and related textural variations of vanadium oxide (V2O5/V2O3) have been exploited to prepare an original composite inorganic porous membrane acting as a 'chemical valve'. A mixture of vanadium and phosphorous molecular precursors were infiltrated into a commercial αA12O3 tubular support. After a thermal treatment in air at 650°C, the pores of the internal and intermediate layers the support were entirely filled with a ceramic material containing V2O5 and A1PO4 crystallites. A number of techniques (FESEM, N2 ads-desorption, Hg porosimetry, XRD, LRS, NMR and TGA) were used to study the morphology, the porous texture and the structural characteristics of the membrane. The red/ox properties of V2O5 crystallites, which transform reversibly to V2O3 under reducing atmosphere, were found to control the porous characteristics of the membrane (grains morphology, pore sizes distribution, and pore volume) and consequently its permeability. The original and reversible membrane red/ox properties were clearly evidenced by single gas permeance and gravimetric studies. The membrane permeance is higher when it is reduced and lower when it is oxidised: the ratio between the permeances of pure n-C4H10 and pure O2 is about 70 at 500°C. The red/ox process was reversible and the membrane permeance behaviour was not altered after 10 red/ox cycles, even under drastic conditions (heating-cooling red/ox cycles with pure gases up to 500°C). This type of infiltrate composite membrane is reproducible, and thermally and chemically stable. © 2001 Elsevier Science B.V. All rights reserved.