Date

2019

Author

Arslan Bozdağ, Arzu

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On site and on-demand hydrogen production through diesel autothermal (ATR) and steam reforming (DSR) reactions are attractive routes for both stationary and mobile auxiliary power unit applications (APUs). Maximization of H2 production with coke minimization for cheap and active Ni/Al2O3 catalysts was investigated with incorporation of different metals/metal oxides to Ni/Al2O3 catalyst in DSR and ATR reactions. Two different synthesis techniques which are impregnation of metal/metal oxides to commercial Al2O3 pellets and one-pot synthesis of metal/metal oxide incorporated Al2O3 through surfactant aided evaporation induced self-assembly (EISA) approach, were applied. The effects of different metals/metal oxides such as Ru, W, CeO2, Mg, ZrO2 and their different combinations such as Ru & CeO2, Mg, CeO2 & ZrO2, W & CeO2, W & Mg on the hydrogen productivity and coke resistivity of Ni/Al2O3 catalyst in DSR and ATR reactions were investigated. Performances of catalysts were investigated at the optimum operating conditions which were found to be 7500 h-1 for GHSV, and 2.5 for H2O/C ratio in DSR reaction, 7500 h-1 for GHSV, 2.5 for H2O/C ratio, and 0.5 for O2/C ratio in ATR reaction. Catalyst investigations presented that among Ru and Ru-CeO2 incorporated catalysts, 0.5 wt.% ruthenium loading results in the highest H2 production in both DSR and ATR. Higher activity of this material was mostly due to its higher surface area and easier reducibility of Ni on Ni@0.5Ru@Al2O3 which also presented long term stability for 34 h. Superior activity in DSR was obtained with CeO2 or CeO2/ZrO2 incorporated (one-pot) Ni/Al2O3-EISA catalysts. However, instabilities in product composition of CeO2/ZrO2 incorporated catalyst observed in DSR suggested that in the long term, incorporation of CeO2 is more preferable. CeO2 incorporated catalyst also presented higher hydrogen production in ATR reaction compared to CeO2/ZrO2 incorporated catalyst. Long term DSR test performed with Ni@10CeO2-Al2O3-EISA lead to superior activity along with stability. Tests on Mg, W, W-CeO2 and W-Mg incorporated (one-pot) mesoporous Al2O3-EISA supported nickel catalysts showed the most successful catalyst as Ni@10Mg-Al2O3-EISA in terms of hydrogen yield in DSR reaction. The stability and superior activity of Ni@10Mg-Al2O3-EISA catalyst was observed in long term DSR activity test. Higher success of this catalysts was due to formation of Ni0 crystals whereas formation Ni4W crystals was observed along with lower surface area and higher acidity in W catalysts, leading to lower water gas shift and reforming reaction rates. However, significant coke minimization was achieved with W catalysts due to low solubility of carbon in Ni4W crystals and also due to WC crystal formation during reforming reactions. The best performing catalysts in this study in terms of hydrogen production was Ni@10Mg-Al2O3-EISA, Ni@0.5Ru@Al2O3 and Ni@10CeO2-Al2O3-EISA. Considering sustainability of the developed catalysts, it is suggested that Ni@10Mg-Al2O3-EISA catalyst can be used in commercial applications of DSR. The highest hydrogen production with low coke deposition in ATR reaction was obtained with Ni@10CeO2-Al2O3-EISA catalyst, which can be used in an APUs equipped with a reformer unit to produce hydrogen for solid oxide fuel cells.

Subject Keywords

Hydrogen., Hydrogen, Tungsten, Ceria/Zirconia, Diesel Reformer

URI

http://etd.lib.metu.edu.tr/upload/12625202/index.pdf
https://hdl.handle.net/11511/45287

Collections

Graduate School of Natural and Applied Sciences, Thesis