Improved sulfur tolerance of Pd–Ru membranes: Influence of H2S concentration and exposure time on the hydrogen flux.

The hydrogen flux of Pd–Ru membranes was investigated after they were exposed to H 2 S at different concentrations and over various period of time. The membranes were characterized by XPS, XRD, SEM, and hydrogen permeation tests. The Pd–Ru membrane exhibits excellent sulfur tolerance. The results show that when exposed to 10–80 ppm H 2 S at 723 K for 7 h, the hydrogen flux remains 57–73%. After removal of 10 ppm H 2 S, 100% recovery of flux is observed, and the flux recovers to 94% and 89% for membranes exposed to 30 ppm and 50 ppm H 2 S, respectively. Irreversible flux loss occurs when the membranes are exposed to 80 ppm H 2 S for 7 h or 30 ppm H 2 S for 72 h. The combination of SEM, XRD and XPS results shows that the presence of Ru on the surface significantly prevents the sulfidation of Pd. The initial rapid decrease in hydrogen flux appears to be mainly due to the blocking of surface sites, exacerbated by the subsequent formation of chemically adsorbed sulfur compounds. The high temperature annealing in H 2 decomposes the chemically adsorbed species. • The Pd–Ru membrane shows excellent sulfur tolerance. • The presence of Ru on the surface significantly prevents the sulfidation of Pd. • The physical adsorption and chemical adsorption of H 2 S occur simultaneously. • Formation of sulfur compounds causes irreversible hydrogen flux loss. [ABSTRACT FROM AUTHOR]