Hydrogen permeation and separation characteristics of a thin Pd-Au/Al 2 O 3 membrane: the effect of the intermediate layer absence

The growing interest towards the hydrogen utilization as energy carrier placed a high demand on hydrogen permeable membranes as compact devices for hydrogen separation and purification. Many studies in this scientific field demonstrated that the composite Pd-based membranes are particularly effective for the aforementioned purposes, particularly if compared to the utilization of self-supported Pd-based membranes for their high cost and mechanical limitations. As a case study, a composite membrane based on a thin Pd-Au (8 ?m of metallic layer and 12 wt% of Au) supported on ?-Al2O3 substrate was produced by electroless plating deposition. Permeation tests were performed with pure gases (H2, N2, CO2, CH4) by varying the temperature between 300 °C and 400 °C and the feed pressure from 150 to 350 kPa. The exponential factor (n-value) in the equation describing the relationship between the hydrogen flux permeating through the membrane and its driving force was analyzed as a function of temperature and pressure variation. An apparent activation energy of 11 kJ/mol has been reached and it is comparable to other data present in the open literature. A H2/N2 ideal selectivity of around 500 was reached at 400 °C and 50 kPa of transmembrane pressure and it remained stable up to 600 h under operation. The presence of defects on the metallic layer has affected the membrane performance in terms of H2 perm-selectivity as testified by the post-mortem analysis on the exhausted membrane.