Hydrogen Fuel Technologies for Vehicular Transportation
Dean, Darrell Christopher
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With continually increasing concern over anthropogenic carbon dioxide emissions and their effect on global climate, the search for alternative fuels, especially for mobile applications such as in vehicles, is of immediate concern. Herein, research towards hydrogen as an alternative energy carrier is discussed; first, with the investigation of “hybrid” hydrogen storage systems that are meant to provide hydrogen for a fully fuel cell powered vehicle via a chemical reaction; and second, that of a thermally regenerative fuel cell system (TRFC) to partially supplant the energy needs of transport trucks by harnessing engine waste heat. Hybrid storage systems are comprised of a heterocyclic carrier that undergoes endothermic hydrogen release (indoline) and an organic hydride that undergoes exothermic release (amine boranes). Different embodiments are considered, varying in the mechanism of exothermic release (thermolysis vs. hydrolysis) and the mode of combination (physical vs. chemical). A thorough investigation into the effect of catalyst, sterics and temperature on the heterogeneously catalyzed dehydrogenation rate of N-heterocycles was executed. A number of trends with respect to the catalyst identity and the level of steric protection around the nitrogen atom were observed. The study towards a TRFC involved an investigation of the heterogeneous hydrogenation of benzylic ketones. Screening of a myriad of different catalysts was performed, including those with various supports, metals and modifications, and the examination of how both the sterics and electronics of the ketone affect the hydrogenation rate. A rapid hydrogenation at relatively low metal loadings and hydrogen pressures with extreme selectivity (>99.9%) is required. To date, however, such a combination has been elusive. The best selectivity was obtained with commercial Pd/SiO2 (99.99%), yet at a low conversion of 6%, after 1 h under 1 atm of H2 at 100 ˚C. In addition to the poor conversion, SiO2 is not electronically conductive and is therefore not fit for this application. The best viable catalyst, then, was a Pd/Vulcan XC-72 (carbon) catalyst made by the author with an observed 14% conversion and 98% selectivity under the same conditions. However, trends in activity and selectivity with respect to the catalyst and ketone have been characterized herein.