EFFECT OF CATALYST OXIDATION-STATE AND STRUCTURE ON THIOPHENE HYDRODESULFURIZATION OVER MODEL MOLYBDENUM CATALYSTS

Activity and product selectivity have been measured for thiophene hydr odesulfurization (HDS) over model silica-supported molybdenum catalyst s at a pressure of 1 atm and at temperatures ranging from 398 to 673 K . The model catalysts feature isolated molybdenum atoms in the +2, +4, and +6 oxidation states and molybdenum dimers with each molybdenum at om in the +4 oxidation state. Silica-supported MoS2, prepared by depos ition and decomposition of (NH4)(2)MoS4, was used for reference. There is a correlation between thiophene HDS activity and molybdenum oxidat ion state, with Mo(II) most active. Thiophene I-IDS activity does not show a significant structure dependence for isolated Mo(IV) versus dim eric Mo(IV) catalysts, Activation energies of 51.5 and 49.9 kJ/mol wer e determined for thiophene I-IDS over Mo(II) and MoS2/SiO2 catalysts, respectively. Butane and butenes are the major products of thiophene H DS with little butadiene detected. Activity and selectivity trends sug gest the HDS reaction is initiated by eta(1) binding of thiophene on t he supported metal catalysts. (C) 1997 Academic Press.