Stability and hydrogen permeation behavior of supported platinum membranesin presence of hydrogen sulfide

Chemical stability for hydrogen sulfide of a platinum composite membrane. c onsisting of a platinum layer supported on a porous alumina tube by a CVD t echnique, was evaluated in comparison with a palladium composite membrane. These composite membranes gave high fluxes comparable to that of a reported palladium composite membrane prepared by an electroless-plating technique, as well as high ideal permselectivity for hydrogen over nitrogen, typicall y 240 for palladium and 210 for platinum at 773 K. When these composite mem branes were in contact with gas stream including hydrogen sulfide, their hy drogen permeability declined rapidly. Many cracks were formed on the surfac e metallic layer of the palladium composite membrane, so that other gases b esides hydrogen permeated mainly through the cracks formed. On the other ha nd, cracks were hardly formed for the platinum composite membrane. It was r eported that the lattice constant of palladium was expanded from 0.39 to 0. 65 nm by sulfidation of the metallic layer, but that of platinum was slight ly changed from 0.39 to 0.35 nm. The difference in the expansion of lattice constant may affect structural change and rupture phenomena of these compo site membranes. After the sulfurized platinum composite membrane was treate d with pure oxygen flow, the hydrogen permeability was recovered up to 50% of that of the fresh membrane. (C) 1999 International Association for Hydro gen Energy. Published by Elsevier Science Ltd. All rights reserved.