| Proton Exchange Membrane (PEM) fuel cells that use hydrogen (H2 ) and oxygen (O2) have shown great promise as future sources of clean, efficient power for several applications including automobiles. To avoid the difficulties encountered in gaseous H2 storage and transport, liquid hydrocarbons could be stored on-board and reformed into H2 via fuel processing. However, carbon monoxide (CO) that is generated by the hydrocarbon reforming processes is a poison to fuel cell platinum (Pt) electrodes and its levels must therefore be reduced. Furthermore, the use of on-board reformers in vehicles severely constrains their design and size.; This thesis explores several novel concepts in reactor design and engineering for fuel processing, with specific focus on a particular reaction in the fuel processing sequence: the preferential oxidation of CO in a H2-rich reformate (PrOx). The results obtained from a silicon microchannel PrOx reactor incorporating a catalytic washcoat have been presented. It was observed that the silicon microreactor performed similar to a packed-bed microreactor, while being much more suited to system scale-up. The thesis also presents the design, fabrication and integration of a Pt thin-film heater with the silicon microreactor system. Thermal and reactor models for the integrated system were developed and validated experimentally, thus establishing a basis for microsystem design.; The use of a two-stage packed-bed microreactor for PrOx has been investigated. It was observed that the two-stage mode operating near a 60:40 O2 split ratio provided better conversion and selectivity than the single-stage mode, and was also more robust in handling disturbances in inlet conditions.; A breadboard fuel processor system was built and tested in a collaborative effort between several research groups at the University of Michigan. The system incorporated micromachined reactor modules with washcoated metal alloy foams, and provided a H2-rich stream required to power a 100 W e fuel cell. Single channel test runs for PrOx confirmed the catalytic activity of the washcoat when coated on the foam. A scaled-up PrOx module (25 layers) offered an outlet CO concentration around 50 ppm at 190°C. |
