The Characterization Of Supported Molybdenum Nitride Catalyst And The 4,6-Dimenthyldibenzothiophene Hydrodesulfurization

The development of new kind of hydrodesulfurization(HDS) and hydrodenitrogenation(HDN) catalysts have been paid more attention because of the more strict environmental regulation. As the traditional transiton-metal sulfide catalysts could not meet these demands, a new type of catalytic materials, transition metal nitrides, carbides and phosphides, which have the quasi-metal quality show the potential good performance in HDS and HDN reaction. More deeply studies have been made on this kind of catalytic materials recently. In this thesis the unsupported molybdenum nitride, supported molybdenum nitride, supported NiMo nitride and supported CoMo nitride catalysts were prepared by nitriding of the oxidic catalysts in the mixture gas of N₂ and H₂. Supported MoP catalyst was prepared by the method of temperature-programmed reduction of phospho-molybdate in H₂. These catalysts were characterized by XRD,BET,NH₃-TPD,XPS,TG-DTA. The HDS and HDN activities of the catalysts were tested by thiophene,4,6-dimethylbenzothiophene(4,6-DMDBT),pyridine,quinolin as the model compounds. The defferences of properties and activities between Mo₂N and MoP catalysts were investigated. The main work and conclusions of this thesis are as below:1. The preparation of Mo₂N and MoP catalysts.The supported Mo₂N, CoMo nitride and NiMo nitride catalysts were synthesized by temperture-programed reaction of the oxidic catalysts with flowing mixture gas of N₂ and H₂(H₂/N₂=5:1).The MoO₃,CoMo oxide and NiMo oxide catalysts were prepared using mechanic and impregnation methods. The supported MoP catalyst was prepared by temperature-programmed reduction of phospho-molybdate in H₂.2. The characterization of the prepared catalysts(1) The Mo₂N/γ-Al₂O₃ catalysts prepared by impregnation method had large BET surface area and the Mo species were well dispersed on support surface.(2)γ-Al₂O₃ (from RIPP)with bigger surface area was a kind of good support. The addition of promoter Co and Ni could block up the micropore and reduce the BET surface area of the Mo₂N/γ-Al₂O₃ catalysts.(3)γ-Al₂O₃ support showed mainly weak acidity, which was helpful for improving hydroprocessing performance. The acid amount of the Mo₂N catalyst was more than that of supportγ-Al₂O₃. Addition of promoter Co resulted in increasing of acid amount of the catalyst.(4) There was stronger interaction between supporter and active Mo species in the Mo₂N/γ-Al₂O₃ catalyst prepared by impregnation method than that of the Mo₂N/γ-Al₂O₃ catalyst prepared by mechanic method.More Mo species on the surface of the Mo₂N/γ-Al₂O₃ catalyst catalyst prepared by impregnation method were oxidized to be high valency state oxides during the passivation process. Addition of promoter Co and Ni atoms could inhibit the oxidagation of Mo species.(5) From in situ TG-DTA experiment it could be concluded that the nitriding treatment of MoO₃ in N₂-H₂ mixture is a two-step reaction process. The reaction pathway is MoO₃→MoO₂→Mo₂N. The DTA results showed that the endothermic peak was attributed to the reduction of MoO₃ to MoO₂ and exothermic peak could be assigned to the nitridation of MoO₂ to Mo₂N. But the nitriding treatment of the supported Mo nitride catalysts obviously was a one-step reaction process due to the interaction of the active species and the support.3. HDS and HDN activities.(1) The HDS activities as below: High reaction temperature and ratio of hydrogen to oil were helpful to the thiophene HDS of the supported Mo₂N catalysts. Addition of proper amount of promoter Co and Ni could improve thiophene HDS activities, but overmuch promoter Co and Ni could decrease the HDS activities. 4, 6-DMDBT HDS activity of supported Mo₂N catalyst was much better than that of unsupported Mo₂N catalyst. 4, 6-DMDBT HDS activity of supported Mo₂N catalyst with Co or Ni promoters was much better than Mo₂N/γ-Al₂O₃ catalyst. The Co-Mo₂N/γ-Al₂O₃ catalyst showed a higher 4, 6-DMDBT HDS activity than Ni-Mo₂N/γ-Al₂O₃ catalyst. The Mo₂N/γ-Al₂O₃ catalyst activated by H2 had a higher 4, 6-DMDBT HDS activity than the unactivated. 4, 6-DMDBT HDS activity of the Mo₂N/γ-Al₂O₃ catalyst prepared using impregnation method was much better than that of the MoO2N/γ-Al₂O₃ catalyst prepared using mechanic method. When FS-2 industrial catalyst was treated using nitriding method from this paper, its industrial diesel oil HDS activity was improved obviously.(2) The HDN activities as below: Promoters Co and Ni had obvious inferenced on quinolin HDN activity of Mo₂N/γ-Al₂O₃ catalyst in lower reaction temperature.4. Comparative study on nitride and phosphide.The Mo₂N/γ-Al₂O₃ catalyst and MoP/γ-Al₂O₃ catalyst prepared at a higher space velocity of reduct gas had larger surface area than those prepared at a lower space velocity of reduction gas. The pore size distribution of Mo₂N/γ-Al₂O₃ catalyst was more complex than that of MoP/γ-Al₂O₃ catalyst. The Mo₂N/γ-Al₂O₃ and MoP/_γ-Al₂O₃ catalyst with larger surface area showed a higher 4, 6-DMDBT HDS activity than those with less surface area. The Mo₂N/γ-Al₂O₃ catalyst had a higher 4, 6-DMDBT HDS activity than the MoP/γ-Al₂O₃ catalyst.