Molybdenum carbide (Mo2C) and Pt/Mo2C catalysts were evaluated for the water gas shift reaction without and with 5 ppm H2S. The Mo2C catalyst was quickly poisoned by sulfur, achieving a rate that was similar to 10% of that prior to sulfur exposure. The Pt/Mo2C catalyst was initially more active than the Mo2C catalyst and deactivated more gradually to a level similar to that for the Mo2C catalyst. X-ray photoelectron spectroscopy revealed Mo2C, MoS2, and S-Mo on the spent catalysts; the Pt/Mo2C catalyst also contained PtS. The results are consistent with Mo2C sites on the Mo2C and Pt/Mo2C catalysts being partially sulfur tolerant, in that these sites could be reactivated on treatment in 15% CH4/H-2 at 590 degrees C. High activity sites associated with Pt nanoparticles were irreversibly deactivated. Residual activities for the Mo2C and Pt/Mo2C catalysts in the presence of H2S appeared to be associated primarily with the presence of MoS2 domains. (C) 2010 Elsevier Inc. All rights reserved.