(570af) Steam Reforming of n-Hexadecane Over Nickel Xerogel Catalysts
AIChE Annual Meeting
Wednesday, November 10, 2010 - 6:00pm to 8:00pm
Energy demand continues to climb as the world population grows. Meanwhile petroleum reserves are diminishing. Developing new energy sources and more efficient technologies is extremely important. At the same time, the level of emissions and exhaust gases needs to be reduced to minimize their contribution to the greenhouse effect. Environmentally friendly energy solutions are being sought, especially for mobile applications. For example, the auxiliary power units (APUs) can increase fuel economy by displacing engine idling. The combination of an on-board reformer and a SOFC would enable commercial fuels such as jet fuel and diesel to be used as a hydrogen source because of the existing infrastructure and high energy density of these fuels. More popular in transportation, military, and industrial applications, commercial fuels could be a good first step toward a hydrogen-based society. Catalytic steam reforming is an efficient process that yields high H2 concentrations. Industrially, hydrogen production is generally conducted by steam reforming of natural gas over nickel-based catalysts, generally supported on alumina and magnesium-aluminate due to their stabilities at high temperatures. Carbon formation is a problem with nickel catalysts in steam reforming; therefore, carbon-resistant catalysts need to be developed. One approach to develop carbon-resistant catalysts is to add a second catalytic specie and another one is to prepare the catalyst with a higher surface area than conventional catalysts. Preparation of metal oxides by the sol-gel method results in the retention of hydroxyl-rich surfaces, which exhibit unique textural and chemical properties compared with those prepared by other conventional methods. Therefore, developing a sol-gel-derived Ru-promoted Ni-CeO2-Al2O3 catalyst for the steam reforming of hexadecane, a surrogate for diesel fuel, is of interest. Steam reforming of n-Hexadecane was carried out with the goal of development of a new and highly active catalyst for hydrogen production. Xerogel and Aerogel Ru-promoted NiO-CeO2-Al2O3 catalysts have been prepared via sol-gel process followed by conventional drying and supercritical drying, respectively. Monometallic base catalysts were also prepared by sol-gel method for comparison purposes. Catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), Hydrogen chemisorption and BET surface area measurements. Catalyst activity and stability were enhanced by the addition of ruthenium to NiO-CeO2-Al2O3 catalysts. Catalyst characterization results suggest that presence of Ru and CeO2 enhance the catalyst reducibility and the resistance to carbon deposition. During the steam reforming of n-Hexadecane, the main reaction products obtained were H2, CO, CO2 and CH4. The 10N3CA (containing 10% nickel and 3% ceria) monometallic catalyst showed lower activity than Ru-promoted Ni catalysts and higher activity than 1R3CA (1% ruthenium and 3% ceria) catalyst. Addition of 1 wt% Ru to the 10N3CA catalyst (1R10N3CA) enhanced the catalyst activity dramatically, increasing hydrogen yield appreciably. This performance is due to a high dispersion of Ni in Ru-promoted catalysts. These results are also supported by the CO2-TPD, TPR, and XRD wherein the total basicity and Ni reducibility are higher for the 1R10N3CA compared to monometallic catalysts. The aerogel 1R10N3CA catalyst showed high catalytic activity, low carbon deposition, good resistance to sintering and prolonged stability compared to the equal mass of the xerogel catalysts, due to its larger pore size and lower bulk density.