To enhance our understanding of the effects of sulfur on the properties of Mo2C and Pt/Mo2C catalysts, methanol steam reforming rates were measured in the absence and presence of 5 ppm H2S. Exposure to H2S quickly deactivated the Mo2C catalyst, although 60% of the initial rates were retained. Deactivation of the Pt/Mo2C catalyst was more gradual and the pseudo-steady state rates approached those for the Mo2C catalyst. Treatment in 15% CH4 in H-2 at 590 degrees C for 4 h restored similar to 100% and similar to 15% of the initial rates for the Mo2C and Pt/Mo2C catalysts, respectively. X-ray photoelectron spectroscopy indicated domains of Mo2C. MoS2 and S-Moon the Pt/Mo2C catalyst surface, but no sulfur was observed on the Mo2C catalyst surface. The results suggested that sulfur selectively poisoned some but not all of the active sites on Mo2C, and irreversibly poisoned the Pt sites producing inactive PtS. (C) 2011 Elsevier B.V. All rights reserved.