Fuel stocks today contain a large percentage of sulfur, nitrogen, and metals. To meet processing and environmental regulations, these components must be removed. Hydrodesulfurization reactions and the use of catalysts to enhance this process have been under extensive study in recent years. The main hydrodesulfurization catalyst used has been cobalt-molybdenum on an alumina support. This study investigated rhodium incorporated zeolites as catalysts for thiophene hydrodesulfurization reactions. The compounds RhCl₃ • 3H₂O, Rh₂(CO₂CH₃)₄, and Rh(PPh₃)₃Cl were adsorbed onto 13X and ZSM5 zeolites. Results of thiophene hydrodesulfurization over RhCl₃-13X and RhCl₃-ZSM5 were compared to those of commercial Co-Mo/Al₂O₃ to determine the most active catalyst under different experimental conditions. X-ray photoelectron spectroscopy, infrared spectroscopy, x-ray diffraction and microelectrophoresis were used to characterize the zeolites. Hydrodesulfurization reactions were carried out in a pulse microreactor/gas chromatograph system as a function of gas flow rate and reaction temperature. Reaction products were identified by mass spectrometry. RhCl₃-13X exhibited maximum thiophene conversion when presulfided with thiophene injections at 100°C, or with a 10 vol% H₂S/90 vol% H₂ gas mixture at 400°C. At a H₂S-sulfiding temperature of 250°C, the commercial Co-Mo/Al₂O₃ catalyst was most active. Over all catalysts, the only reaction products were hydrogen sulfide, butene and butane. The butene/butane product ratio increased with increasing temperature. On the basis of these results and XPS measurements, Rh(I) was identified as the active hydrodesulfurization species. / Master of Science