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.