Studies on characterization of sulfided tertiary NiMoP/gamma-Al2O3 catalysts by TPR technique and their thiophene HDS activity

A series of sulfided tertiary NiMoP/gamma -Al2O3 catalysts with different contents of MoO3 were prepared by using molybdophosphoric acid of Keggin structure (H3PMO12O40) and nickel nitrate as origins of active phase components of molybdenum, phosphorus and nickel, and characterized by TPR technique, with their HDS activity being investigated with thiophene as a model substrate. For the sulfided Mo-O catalyst containing no nickel as promoter, the only hydrogen sulfide evolution peak I is observed at 462 K and attributed to the hydrogenation of the so-called edge sulfur atoms chemisorbed on coordinatively unsaturated(cus) Mox+ sites on the MoS2 phase(MoS2 slab). With the introduction of nickel into the active phase of the sulfided Mo-O catalyst and with the increase of the molybdenum loading, a new hydrogen sulfide evolution peak II gradually develops at the low temperature side of;he peak I, at the same time accompanied by both the increase of the area ratio of the peak II to the peak I and the shift of the hydrogen sulfide evolution maximum rate to lower temperatures, which may imply the existence of two kinds of active centers related to molybdenum and nickel respectively and the synergic action between the two centers above. It should be noted that for the sulfided NiMoP/gamma -Al2O3 catalysts, the thiophene HDS rate and the quantity of hydrogen sulfide evolved during TPR process increase monotonously with the atomic ratio of molybdenum to nickel in the form of [n(Ni)+n(Mo)]/n(Ni). On the basis of the results here, the conclusion may be reached that the two kinds of vacancies can be formed on the edge of Ni-Mo-S slab due to the loss of S during TPR process and vacancies or sites related to the H2S evolution peak II should be regarded as the mainly active reaction centers of thiophene I-IDS