(401e) The Interaction Of Sulfur Containing Compounds With Nickel-Ceria-Zirconia Catalysts During The Autothermal Reforming Of Hydrocarbon Fuels

Fuel cells offer a promising opportunity for cleaner and more efficient mobile power generation. However, the supply of hydrogen rich feed streams in mobile fuel-cell based power applications is an ongoing challenge. One possibility is the application of onboard reforming of commercial or logistics fuels. The main obstacles to this approach have been carbon deposition and sulfur poisoning, each leading to decreased catalyst activity. Previous work has demonstrated that the oxygen storage capacity of ceria-zirconia support (CZO) has decreased the propensity of Ni to coke during the autothermal reforming of isooctane and n-dodecane (model compounds for gasoline and jet-fuel respectively). It has been shown that adjusting the nickel loading of the catalyst and the oxygen to carbon ratio in the feed stream strongly affects the relative contribution of steam reforming and partial oxidation to the overall product composition. The goal of this work is to understand the effect of sulfur-containing feeds on nickel-ceria-zirconia catalysts. Through the combination of reaction and characterization (TPD, TPR, XPS, XRD, TGA) studies, this work endeavors to develop a proposed mechanism of sulfur poisoning and suggest appropriate regenerative protocols and/or guide future development of sulfur tolerant materials. Preliminary results have shown the effect of sulfur on the nickel-ceria-zirconia family of catalysts. Under autothermal reforming conditions (O/C = 0.75, H2O/C = 1.0, T = 500 °C, GHSV = 200,000 /hr) 10 wt% Ni/Ce0.75Zr0.25O2 shows stable performance over 10 hours with 0 ppm sulfur. When thiophene is added to the isooctane to give 515 ppmw sulfur, the reforming performance shows rapid deactivation during the first three hours, followed by much slower deactivation from three to nine hours. The hydrogen and carbon monoxide yield trends are similar, while the carbon dioxide yield shows almost no deactivation. The addition of sulfur also increases the catalyst temperature during operation. These observations taken together suggest that sulfur poisons reforming sites (probably nickel), but has less of an effect on oxidation sites (probably ceria-zirconia). When the catalyst is exposed to sulfur dioxide at various temperatures, temperature programmed desorption shows at least two types of sulfur species. One is removed between 150 and 300 °C, depending on the adsorption temperature, while the other is not removed until 1000 °C. Increasing the adsorption temperature decreases the species removed at low temperature but increases the one removed at high temperature. XPS confirms the presence of sulfur on the catalyst.