Palladium (Pd)-based membranes have been studied for many years, regarding applications in production and purifi-cation of hydrogen. The reaction of water gas shift (CO+ H2O ↔ CO2 + H2), for example, can advantageously be conducted in a Pd-based membrane reactor, where hydrogen produced selectively permeates the membrane [1]. When hydrogen permeates with an infinite selectivity, its passage is governed by sorption-diffusion mechanism through the atomic struc-ture.
Among all metals, palladium is the material that exhibits the highest atomic hydrogen permeability, resulting from the high capability in the catalytic dissociation of H2 molecules it in its metallic structure [2]. However, the use of pure palladi-um membranes has some limitations [3]. When palladium alloys such as Pd-Ag are used, the result is a homogeneous solid solution with a fcc structure [4,5]. This alloy prevents the formation of hybrid phases, allowing higher hydrogen permeation along with chemical and mechanical stability, reducing also the overall cost of raw material [2].Patricia Pérez is grateful to Fundação para a Ciência e a Tecnologia (FCT) for the doctoral grant (reference: SFRH/BD/73673/2010). The authors also acknowledge fi-nancing from FCT through the project PTDC/EQU-ERQ/098730/2008 and COMPETE scientific program. The authors show appreciation for the collaboration of Sandra Rodrigues on the permeation experiments
