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

In this work, the reversible red/ox properties and related textural variati ons of vanadium oxide (V2O5/V2O3) have been exploited to prepare an origina l composite inorganic porous membrane acting as a 'chemical valve'. A mixtu re of vanadium and phosphorous molecular precursors were infiltrated into a commercial alpha Al2O3 tubular support. After a thermal treatment in air a t 650 degreesC, the pores of the internal and intermediate layers the suppo rt were entirely filled with a ceramic material containing V2O5 and AlPO4 c rystallites. A number of techniques (FESEM, N-2 ads-desorption, Hg porosime try, XRD, LRS, NMR and TGA) were used to study the morphology, the porous t exture and the structural characteristics of the membrane. The red/ox prope rties of V2O5 crystallites, which transform reversibly to V2O3 under reduci ng atmosphere, were found to control the porous characteristics of the memb rane (grains morphology, pore sizes distribution, and pore volume) and cons equently its permeability. The original and reversible membrane red/ox prop erties were clearly evidenced by single gas permeance and gravimetric studi es. The membrane permeance is higher when it is reduced and lower when it i s oxidised: the ratio between the permeances of pure n-C4H10 and pure O-2 i s about 70 at 500 degreesC. The red/ox process was reversible and the membr ane 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 degreesC). This type of infiltrate composite membrane is reproducible, and thermally and chemically stable, (C) 2001 Elsevier Science B.V. All rights reserved.