Two new large scale (200 cm(2)) composite Pd and Pd-Au membranes were prepared and tested in an actual coal derived, but desulfurized, syngas in order to further,quantify permeance loss, due to species other than sulfur and to determine the nature of the contaminants. As in our previous work, membranes were tested at the National on;Capture Center (NCCC) in Wilsonville, Alabama. Before the syngas test, the Pd and Pd-Au membranes had thic esses of 7 and 6.6 mu m, H-2 permeance at 450 degrees C of 17.7 and 29.2 N m(-2) h(-1) bar(-0.5), and H-2/He selectivities higher than 2700 and 160 000, respectively. The two membranes produced H-2 at an exceptionally high purity level of 99.8-99.9%. The selectivity of the Pd-Au membrane stable was for over 473 h in ctual sy-ngas atmosphere at 450 degrees C and 12.6 bar demonstrating the high robustness and suitability of these membranes in industrial environments. However, as seen in our previous study, the,two, membranes showed a decrease in H-2 permeance upon syngas introduction (ranging from 40 to 50%), indicating, the presence of a fast surface poisoning, process. The XPS analysis of a Pd coupon attached to the Pd membranes, and therefore exposed to the same syngas as the Pd membranes, revealed the presence of Mg, Na, Hg, O, C, and S on its surface. Furthermore, depth profile analysis revealed the presence of C at a concentration level of 4 atom % at a depth of 1.1 mu m. Tests in pure H-2 atmosphere at 450 degrees C after, syngas exposure resulted in a moderate. permeance recoverability, for the pure Pd membrane (77%), while an outstanding 100% recoverability was achieved with the new Pd-Au alloy. Compared to our previous study, the Pd-Au membrane had a thicker Au layer on its surface (approximately 0.5 mu m instead of 0.2 mu m) that was intended to better mitigate surface poisoning by syngas contaminants. The average Au content of the layer with the Au gradient (2.2 mu m, in thickness was determined by XRD and equaled 23 atom %.