Influence of H₂S on the hydrogen flux of thin-film PdAgAu membranes

Pd-based membranes have the potential to be used for hydrogen purification and production in membrane reactors. However, the presence of impurities in the feedstock, such as H2S can poison the membrane, thus decreasing the hydrogen permeation by blocking and deactivating active sites of the Pd-alloy on the membrane surface. H2S at high concentrations can even destroy the membrane by the formation of Pd4S. It is known that alloying of Pd with Au enhances the membrane resistance to H2S. This work reports the performance of six PdAgAu/Al2O3 supported membranes, prepared by electroless plating combined with PVD under exposure to trace amounts (<2 ppm) of H2S. The Au content shows not to play a significant role at these low concentrations. Exposure results suggest a dual influence of physisorbed H2S and chemisorbed S species. A Langmuir description shows that the influence of the partial pressure of hydrogen is negligible on the flux inhibition. In the post characterization the absence of Pd4S was shown, however the surface was affected by the exposure to H2S.