(82b) Influence of Thiophene On Autothermal Reforming of Isooctane Over Nickel Catalysts

Autothermal reforming (ATR) is an attractive option for the catalytic production of hydrogen from various hydrocarbon based feeds. ATR offers a balance between the prohibitive heat transfer demands of steam reforming and the excessive carbon deposition of partial oxidation. Among the great challenges of ATR is the propensity of transition and noble metal catalysts to deactivate in the presence of even low feed levels of organosulfur compounds. The development of more sulfur tolerant reformers is impeded by the complex reaction environment typically seen in ATR reactors. While the behavior of various sulfur molecules has been well developed for a broad range of model catalytic surfaces, there is still a lack of understanding as to the behavior of molecules such as thiophene under reaction conditions. This presentation will discuss the pursuit of a better understanding of the behavior of thiophene on the ATR of isooctane, a model compound for gasoline. A nickel-based catalyst supported on a mixed oxide of ceria and zirconia was used for this study. Care was taken in the reactor design to insure the inertness of transfer lines to the adsorption of organosulfur compounds. System parameters such as oxygen-to-carbon ratio, steam-to-carbon ratio, space velocity, and thiophene concentration were varied to explore the effects and reactivity of thiophene, under varying reaction environments. The composition of the reactor effluent was compared to calculated equilibrium compositions. It was found that the reactivity of thiophene was dependent upon the feed concentration of oxygen and correlated well with the overall activity and stability of the ATR reactor towards the production of hydrogen and carbon monoxide. Post-reaction characterization of the catalyst bed gave a more complete view of the reaction environment. Atomic emission spectroscopy, temperature programmed reduction and diffuse reflectance infrared spectroscopy described the sulfur adsorbed on the catalyst while temperature programmed oxidation was used to quantify the carbon deposition rate under the various reaction conditions.