Dense cermet (i.e., ceramic-metal composite) membranes have been developed for separating hydrogen from mixed gases, particularly product streams generated during coal gasification and/or steam methane reforming. Hydrogen separation with these membranes yields high-purity hydrogen, thereby eliminating the need for post-separation purification steps. Extensive tests have been conducted with cermet membranes made by mixing approximate to 50-60 vol.% Pd with Y2O3-stabilized ZrO2. Using several feed gas mixtures, the hydrogen permeation rate, or flux, for the membranes was measured in the temperature range 400-900 degrees C. With pure hydrogen at ambient pressure as feed gas, an approximate to 18-mu m-thick membrane on a porous substrate gave a measured flux of approximate to 26 cm(3)[STP]/min-cm(2) at 400 degrees C and approximate to 52 cm(3)[STP]/min-cm(2) at 900 degrees C. We also measured the hydrogen flux through a thicker (approximate to 150 mu m) membrane at 400 degrees C using a mixture of H-2, CO, CO2, H2O, and He at approximate to 200 psig as feed gas. Hydrogen flux measurements in H2S-containing atmospheres showed that the cermet membranes are stable at 900 degrees C in gases that contain approximate to 80% H-2/400 ppm H2S. Because formation of palladium sulfide (Pd4S) can seriously degrade hydrogen permeation through Pd-containing cermet membranes, the Pd/Pd4S stability phase boundary of the cermet membrane was determined in the temperature range 450-650 degrees C using various feed gases that contained 10-73% H-2 and 8-400 ppm H2S. Given these promising results, longer studies using real-world coal gasification conditions should be pursued. (C) 2013 Elsevier B.V. All rights reserved.