STUDIES ON THE HYDRODESULFURIZATION ACTIVITY OF MOLYBDENA AND TUNGSTA CATALYSTS PROMOTED BY COBALT AND NICKEL

Investigation of thiophene hydrodesulphurisation over a series of nickel molybdena catalysts showed that activity of catalyst increased with Ni loading passing through a maximum at a composition, Ni/Ni + Mo = 0.47. On comparing the promoter function of Ni with that of Co in molybdena/tungsta catalysts, it was found that tungsta catalysts have very low activity compared to molybdena catalysts. Nickel molybdena showed high starting activity, which decreased with pulse number to a steady state. This is explained by assuming dual sites consisting of anion vacancies and surface oxide sites. In pulse reaction smaller pulses gave higher conversion since H-2-thiophene ratio in smaller pulse is higher. This is much pronounced in highly active molybdena catalysts compared to less active tungsta catalysts. The extent of reducibility of oxide catalysts was found to determine the activity. On n-butyl amine poisoning, the decrease in thiophene conversion was more for active sites. Promotional influence of nickel in molybdena catalysts was also observed in continuous flow reactor.