99.7% conversion of CO in a simulated syngas feed containing 53% CO, 35% H-2 and 12% CO2 was achieved via the water-gas shift (WGS) reaction in a counter-current Pd multi-tube membrane reactor (MR) at 1173 K and 2s residence time. This conversion is significantly greater than the 32% equilibrium conversion associated with a conventional (non-membrane) reactor primarily due to the high rate of H-2 extraction from the reaction zone through the Pd membranes at elevated temperatures. Furthermore, nearly complete H-2 recovery was attained in the permeate, resulting in the simultaneous production of a high-pressure CO2 (>99%) retentate stream after condensation of the steam. When Pd80wt%Cu tubes were used in the reactor, a significantly lower CO conversion of 68% was attained at comparable residence times, probably due to the lower H-2 permeance of the alloy. When H2S was added to the syngas feed and the H2S-to-H-2 ratio was maintained below the threshold required for thermodynamically stable sulfides to form, the Pd and Pd80wt%Cu MRs retained their mechanical integrity and H-2 selectivity, but a precipitous drop in CO conversion was observed due to deactivation of the catalytic surface. The Pd and Pd80wt%Cu MRs were observed to fail within minutes after increasing the H2S-to-H-2 ratio to levels above that expected for thermodynamically stable sulfides to form, as evidenced by rupturing of the membrane tubes. SEM-EDS analyses of the membranes suggested that at high H2S-to-H-2 ratios, the H2S compromised the mechanical integrity of the MRs by preferentially attacking the grain boundary region. (C) 2007 Elsevier B.V. All rights reserved.