(386d) Influence of Pt Addition On the Performance of Pd-Au Hydrogen Separation Membranes

Palladium alloys have been extensively studied as hydrogen separation membranes with the permeability directly proportional to both solubility and diffusion.  Using Density Functional Theory (DFT), we have calculated that the addition of Au improves solubility of H over pure Pd but the addition of Pt has almost no effect.  Unlike in the solubility analysis, DFT calculated that the addition of Au and Pt negatively effects diffusion of H in binary systems.   Given these modeled results, experiments were performed using binary Pd-Au and ternary Pd-Au-Pt alloys.  In pure H₂, a Pd-Au alloy exhibited higher permeabilities than pure Pd, which is in agreement with published values for membranes of similar compositions. The addition of Pt in concentrations ranging from 4.3 to 12.9 wt% lowered the permeability in pure hydrogen to slightly below pure Pd. For thicker (25 µm) Pd-Au-Pt membranes pretreated in air (versus nitrogen) at 400°C before exposure to H₂, an increase in permeability of 10-20% was observed. The hydrogen permeability, was depressed both by water-gas shift mixtures (with or without H₂S), but it appears that either substantial quantities (20 wt%) of Au or the presence of Pt in the Pd alloy (or both) inhibit sulfide formation, thereby improving both permeability and stability in WGS conditions with H₂S.   In this presentation, the predicted performance of the addition of Pt will be compared with experimentally measured values and a discussion of the influence of Au and Pt on the sulfur tolerance of the membranes will be presented.