Hydrodesulfurization of dibenzothiophene over supported and unsupported molybdenum carbide catalysts

A series of gamma-Al2O3 supported molybdenum carbides [carbided Mo/gamma-Al 2O3 (MCS), Co-Mo/gamma-Al2O3 (CMCS), and Ni-Mo/gamma-Al2O3 (NMCS)] and unsu pported molybdenum carbide (MCUS) were prepared by the temperature-programm ed carburization of their corresponding molybdenum nitrides with 20% CH4/H- 2. XRD and SEM studies show that unsupported molybdenum carbide catalyst po ssesses a typical crystalline Mo2C (FCC structure), while supported molybde num carbide catalysts possess highly dispersed surface molybdenum carbide s pecies on an alumina oxide support. The results of dibenzothiophene (DBT) h ydrodesulfurization over molybdenum carbide catalysts show that the reactiv ity is strongly dependent on the type of catalyst. Supported molybdenum car bide catalysts possess a higher reactivity than the unsupported molybdenum carbide catalyst. In addition, Co or Ni promoted, supported molybdenum carb ide catalyst possesses a higher reactivity than the unpromoted, supported m olybdenum carbide catalyst. The reactivity, which is also dependent on the reaction conditions, increases with increasing reaction temperature and pre ssure and contact time. The CO uptakes of the molybdenum carbide catalysts correlate well with overall activity (total rate) for DBT hydrodesulfurizat ion. The major reaction product is biphenyl with cyclohexylbenzene next in abundance regardless of the type of catalysts and reaction conditions. It w as also found that the molybdenum carbide catalysts exhibit stable initial reactivity due to the stable and weak acidic characteristics of these catal ysts.