Study On Hydrogen Production From Steam Reforming Of Ethanol On Nickel-Based Catalyst Prepared From FC Structured Precursor

Most of the present world energy supplys comes from fossil fuels. But reserves of fossil fuels are limited. People recognize that reserves of petroleum, natural gas and coal are finite for providing energy. Unlike fossil fuels, hydrogen can burn cleanly, without emitting any environmental pollutants. FCs use hydrogen as a fuel which results in the formation ofwater vapor only and thus they provide clean energy. H2 is considered to be the energy carrier of the future and could have an important role in reducing environmental emissions. Currently, most of the H2 is produced via the steam reforming of fossil fuels. However, hydrogen production from fossil fuels is always associated with the emission of greenhouse gases and local pollutants. In nature, H2 can be produced from different resources. Among the liquid H2 resources, ethanol is a good candidate for several reasons. Ethanol is renewable and is becoming available easily. It is easy to transport, biodegradable, and low in toxicity.A thermodynamic analysis of ethanol oxidative steam reforming was carried out with a Gibbs free energy minimization method. The addition of oxygen lowers the enthalpy of the system and favors the heat recycle. Thermal-neutral conditions are obtained, at which the heat released from exothermic reactions makes up exactly for the requirement of the endothermic reactions. Thermal-neutral temperature is a function of the feed composition. For 700 K thermal-neutral conditions can be reached in a wide range of H2O/EtOH and O2/EtOH ratios. However, this condition is not practical because that a catalyst active in the range is difficult to find. At 900 K, a given condition range exists for thermal-neutral operation. At 1100 K, no thermal-neutral condition exists in the condition range examined. Under thermal-neutral conditions, the equilibrium moles of hydrogen, methane, carbon monoxide and carbon are examined. 900 K is favorable for hydrogen production where the maximum equilibrium mole of hydrogen appears. For the non- thermal-neutral operations, a detailed calculation is presented on a range of reaction conditions, i.e. temperature 700– 1100 K, H2O/EtOH and O2/EtOH feed ratios in 1.0– 10.0 and 0.0– 0.9, respectively. The equilibrium moles of H2, CH4, CO and C are examined. Hydrogen is favored at low O2/EtOH ratio, high H2O/EtOH ratio and 900 K. Methane is not favored at high temperatures and high O2/EtOH and H2O/EtOH ratios. Carbon formation can be avoided by adjusting the reaction condition in a reasonable range.The ethanol steam reforming over nickel supported catalysts with different Ni loadings prepared from Feitknecht compound precursors was studied. By varying the Ni loading, Ni dispersion and nickel phases could be controlled. It was found that the amount of Mg in the catalyst affect the acidity of support. It was shown that NiMgAl-0.5 catalyst obtained from Feitknecht compound precursor showed the best activity, selectivity and resistance to carbon deposition. The deposited carbon has a filamentous structure after 100 hour, and the size of Ni particles only increased slightly.Feitknecht compound precursor for preparing mixed oxide catalyst has been successfully synthesized by a novel method. And the mixed oxide obtained from the above method was applied in ethanol steam reforming. Furthermore, for comparison, catalysts prepared from conventional coprecipitation and impregnation methods had the same composition with the catalyst prepared from the new method. The high BET surface area of the catalyst obtained from reverse microemulsion method enhanced the nickel dispersion and the nickel surface area. The catalyst obtained from reverse microemulsion exhibited the best activity, stability, and least carbon deposition. Feitknecht compound precursors for preparing lanthanide promoted catalysts have been applied to ethanol steam reforming. The results showed that the surface area increased greatly for lanthanide promoted catalysts. And there was an optimal value for lanthanide promoted contents. XRD of the mixed oxides indicated that a small amount of La3+ was doped into the Ni-Mg-O solid solution and CeO2 was conglomerated on the surface of the support. TPR results revealed that the presence of lanthanide elements enhanced the catalyst reducibility, which was most evident with lanthanum promoted catalysts. XPS data indicated that lanthanum promoted catalysts exhibited higher Ni0 concentration on surface area compared to cerium promoted catalysts. XRD of the used catalysts indicated that lanthanum prevented the growth of crystallite sizes. Activity experiments showed that adding small amounts of lanthanide elements could improve the catalytic activity and stability significantly.