Heavy-duty trucks are in idle operation during long periods of time, providing the vehicles with electricity via the alternator at standstill. Idling trucks contribute to large amounts of emissions and high fuel consumption as a result of the low efficiency from fuel to electricity. Auxiliary power units, which operate independently of the main engine, are promising alternatives for supplying trucks with electricity. Fuel cell-based auxiliary power units could offer high efficiencies and low noise. The hydrogen required for the fuel cell could be generated in an onboard fuel reformer using the existing truck fuel. The work presented in this thesis concerns hydrogen generation from transportation fuels by autothermal reforming focusing on the application of fuel cell auxiliary power units. Diesel and dimethyl ether have been the fuels of main focus. The work includes reactor design aspects, preparation and testing of reforming catalysts including characterization studies and evaluation of operating conditions. The thesis is a summary of five scientific papers. Major issues for succeeding with diesel reforming are fuel injection, reactant mixing and achieving fuel cell quality reformate. The results obtained in this work contribute to the continued research and development of diesel reforming catalysts and processes. A diesel reformer, designed to generate hydrogen to feed a 5 kWe polymer electrolyte fuel cell has been evaluated for autothermal reforming of commercial diesel fuel. The operational results show the feasibility of the design to generate hydrogen-rich gases from complex diesel fuel mixtures and have, together with CFD calculations, been supportive in the development of a new improved reformer design. In addition to diesel, the reforming reactor design was shown to run satisfactorily with other hydrocarbon mixtures, such as gasoline and E85. Rh-based catalysts were used in the studies and exhibit high performance during diesel reforming without coke formation on the catalyst surface. An interesting finding is that the addition of Mn to Rh catalysts appears to improve activity during diesel reforming. Therefore, Mn could be considered to be used to decrease the noble metal loading, and thereby the cost, of diesel reforming catalysts. Dimethyl ether is a potential diesel fuel alternative and has lately been considered as hydrogen carrier for fuel cells in truck auxiliary power units. The studies related to dimethyl ether have been focused on the evaluation of Pd-based catalysts and the influence of operating parameters for autothermal reforming. PdZn-based catalysts were found to be very promising for DME reforming, generating product gases with high selectivity to hydrogen and carbon dioxide. The high product selectivity is correlated to PdZn interactions, leading to decreased activity of decomposition reactions. Auxiliary power systems fueled with DME could, therefore, make possible fuel processors with very low complexity compared to diesel-fueled systems. The work presented in this thesis has enhanced our understanding of diesel and DME reforming and will serve as basis for future studies. / QC 20100804

Heavy-duty diesel truck engines are routinely idled at standstill to provide cab heating or air conditioning, and in addition to supply electricity to comfort units such as radio and TV. Idling is an inefficient and unfavorable process resulting in increased fuel consumption, increased emissions, shortened engine life, impaired driver rest and health, and elevated noise. Hydrogen-fueled, polymer-electrolyte fuel-cell auxiliary power unit (PEFC-APU) as a silent external power supply, working independently of the main engine, is proposed as viable solution for better fuel economy and abatement of idling emissions. In a diesel PEFC-APU, the hydrogen storage problem is circumvented as hydrogen can be generated onboard from diesel by using a catalytic reformer. In order to make catalytic diesel PEFC-APU systems viable for commercialization research is still needed. Two key areas are the development of reforming catalyst and reformer design, which both are the scope of this thesis. For diesel-reforming catalysts, low loadings of Rh and RhPt alloys have proven to exhibit excellent reforming and hydrogen selectivity properties. For the development of a stable reforming catalyst, more studies have to be conducted in order to find suitable promoters and support materials to optimize and sustain the long-term performance of the Rh catalyst. The next step will be full-scale tests carried out at realistic operating conditions in order to fully comprehend the overall reforming process and to validate promising Rh catalysts. This thesis can be divided into two parts; the first part addresses the development of catalysts in the form of washcoated cordierite monoliths for autothermal reforming (ATR) of diesel. A variety of catalyst compositions were developed containing Rh or RhPt as active metals, CeO2, La2O3, MgO, Y2O3 as promoters and Al2O3, CeO2-ZrO2, SiO2 and TiO2 as support materials. The catalysts were tested in a bench-scale reactor and characterized by using N2-BET, XRD, H2 chemisorption, H2-TPR, O2-TPO, XPS and TEM analyses. The second part addresses the development and testing of full-scale reformers at various realistic operating conditions using promising Rh catalysts. The thesis shows that a variety of Rh on alumina catalysts was successfully tested for ATR of diesel (Papers I-IV). Also, zone-coating, meaning adding two washcoats on specific parts of the monolith, was found to have beneficial effects on the ATR catalyst performance (Paper II). In addition, RhPt supported on CeO2-ZrO2 was found to be one of the most active and promising catalyst candidates for ATR of diesel. The superior performance may be attributed to higher reducibility of RhiOx species and greater dispersion of Rh and Pt on the support (Paper IV). Finally, two full-scale diesel reformers were successfully developed and proven capable of providing high fuel conversion and hydrogen production from commercial diesel over selected Rh catalysts (Papers II-III, V-VI). / QC 20110418