Autothermal Reforming of Simulated Fuels

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Helsinki University of Technology | Diplomityö
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Teknillinen kemia
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ix + 94 s. + liitt. 39
The aim of this Master's thesis was to find ways to maximise the production of hydrogen and carbon monoxide for solid oxide fuel cell applications by means of external autothermal reforming (combination of steam reforming and partial oxidation) of hydrocarbon fuels. The literature review presents steam-reforming hydrogen production techniques. Various noble metals and support materials suitable for the reforming catalyst are presented, as well as the preparation of the catalysts and the effect of the preparation procedure on the catalytic performance. In the experimental part, zirconia-supported Rh (0.5 and 1 wt-%), Pt (0.5 wt-%) and Rh/Pt (0.5, 1 and 2 mol/mol) catalysts were prepared and tested in the autothermal reforming of single hydrocarbons and their mixture. The main goal was to prevent metal sublimation from the catalyst' s surface and to improve methane production. Catalyst deactivation was also studied and the operation conditions were optimised. Commercial diesel was simulated using a mixture of toluene, methylcyclohexane and n-heptane (molar ratio 20/50/30). For the catalyst testing in autothermal conditions, steam and oxygen were also added to the system. Based on thermodynamic calculations, the temperature range studied was 400 - 700 °C, because in this range, hydrogen and methane production should he maximised and metal sublimation from the catalyst should be avoided. The monometallic Rh and the bimetallic Rh/Pt catalysts were found to be active in autothermal reforming reactions, while the monometallic Pt catalyst showed similar behaviour to the support. The amount of hydrogen in the product stream on the Rh/Pt 1 mol/mol catalyst was 35 mol-% which was higher than the value achieved with the monometallic Rh catalyst (28 mol-%). The methane amounts achieved on all the catalysts were lower than 1 mol-%. The results showed that 0.2 g of Rh/Pt 1 mol/mol catalyst was appropriate under the experimental conditions as larger amounts of catalyst did not increase the hydrocarbons conversions or selectivity towards hydrogen. It was demonstrated that the hydrocarbons do not compete for the active sites of the monometallic catalysts, while on the bimetallic catalysts competition exists indicating a different total reaction mechanism. Metal sublimation was only noticed on Rh catalysts, but the presence of Pt was found to have a stabilising effect on the bimetallic catalysts, as no reduction in the metal content was observed in the temperature range studied.
Krause, Outi
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Kaila, Reetta
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