The effects of sulfur and oxygen on the catalytic activity of molybdenum carbide during dry methane reforming

The sulfur tolerance of bulk Mo2C catalyst has been evaluated for dry methane reforming (DMR) at 1050 degreesC, in the presence of dimethethylsulfide (DMS) at sulfur concentrations as high as 500 ppm. In addition, the effect of coupling the exothermic partial oxidation of methane with the highly endothermic reforming reaction was also investigated. It was determined that both DMS decomposition and partial oxidation take place in the gas phase, upstream of the catalyst bed, with CS2 as the primary DMS decomposition product. The CS2 was found to reversibly adsorbs on the catalyst surface, resulting in a stable but decreased activity. This conclusion was corroborated by examining the effects of DMS concentration, temperature, and in situ regeneration, and all are consistent with the occurrence of reversible sulfur chemisorption. Evidence is also presented to show that sulfur adsorption during DMR changes the redox chemistry of the catalyst, resulting in a slow oxidation of the surface. On the other hand, stable activity was maintained with oxygen in the feed and is attributed to lower CO2 concentrations under these conditions. Comparison experiments with a supported Rh catalyst gave superior results with respect to sulfur tolerance during DMR, suggesting that sulfur poisoning of noble metal catalysts may not be a serious problem at the high temperatures used in methane reforming, (C) 2004 Elsevier B.V. All rights reserved.