New techniques to modify inorganic membranes have been developed using hydrolytic decomposition of titanium tetraisopropoxide (TTIP) in supercritical propan-2-ol. Solid anatase particles of about 30 nm size are deposited as a thin film on the surface and in the pores of alumina supports in a Batch reactor. The deposition location was found at the support face in contact with the titanium alkoxide solution. With TTIP concentration equal to 0.1 mol l(-1),TiO2 anatase him thickness increases from 1 to 3 mu m when supercritical treatment cycles are raised from 1 to 3. The penetration depth around 20-30 mu m is found to be independent of either the reactant concentration or the treatment number. Finally, the separation selectivity determined from permeation measurement of H-2 and N-2 is close to the value predicted by the Knudsen diffusion model. (C)2000 Published by Elsevier Science S.A. All rights reserved.