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Preparation, Characterization And Activity Of Supported Molybdenum Nickel Phosphides And Molybdenum Nickel Sulfur Clusters Catalysts For Deep Hydrodesulfurization

Posted on:2006-02-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:F X SunFull Text:PDF
GTID:1101360155952338Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Interest in the development of novel catalysts for hydrodesulfurization hasbeen spurred by the need to meet stringent environmental regulations that haverecently been enacted throughout the world. Bulk and supported binary andternary phosphides, molybdenum phosphide, nickel phosphide and nickelmolybdenum phosphide have been prepared by temperature-programmedreduction method and characterized by X-ray diffraction (XRD), BET surface area,CO chemisorption, transmission electron microscopy (TEM) and (31)P MAS NMRand in-situ infrared spectroscopy (IR). The hydrodesulfurization (HDS) activitiesof dibenzothiophene (DBT) were compared for these phosphide catalysts. In orderto gain insight into the nature of the phosphide catalysts under HDS conditions,the surface sites of reduced and sulfided phosphide catalysts were studied by IRspectroscopy using CO as the probe molecule.The activities of the phosphides follow the order Ni2P/SiO2 > Ni-Mo-P/SiO2> MoP/SiO2. The HDS activities of phosphide catalysts don't decline with thetime on stream for at least 20 h. Nickel phosphide has the highest HDS activityamong these phosphide catalysts. The Ni sites in the Ni-Mo-P/SiO2 catalysts playa major role in the conversion of DBT, and the activity of the catalysts increaseswith increasing Ni content. This is different from sulfides, nitrides, and carbides,as no synergetic effect is observed between the phosphided Ni and Mo atoms. Italso suggests that Ni species more easily expose at the surface of the NiMoPparticles. The suface of a working Ni2P/SiO2 catalyst may be a nickelphosphosulfide (i.e., NiPxSy) phase. This unique surface composition of NiPxSy isassumed to be responsible for the excellent HDS activity of the Ni2P/SiO2 catalyst.The IR results indicate that the surface of these phosphide catalysts is partiallysulfided while the structure of the phosphides is retained under HDS reactionconditions. The sulfided phosphide surface can be fully regenerated to a freshphosphide catalyst under mild conditions. For molybdenum phosphide, nickelphosphide, and nickel molybdenum phosphide catalysts, the transformation ofDBT takes place mainly through direct desulfurization yielding biphenyl. Thiswork demonstrates that the nickel phosphide is potentially a promising catalyst forhydrodesulfurization processing. Bulk and supported transition metal molybdenum carbide were prepared.HDS reaction test results indicate that the addition of P, Co and Ni can increasethe HDS activities of β-Mo2C catalyst. The activities of β-Mo2C catalystgradually decrease with the reaction time on stream, this is different from MoPcatalyst. Molybdenum sulfur clusters with [Mo3S4(H2O)9]4+ and [Mo3NiS4 (H2O)10]4+cores were prepared. The catalyst prepared by the Mo3S4 cluster precursor hassmaller metal particle size, better metal dispersion on the support, and higher HDSactivities than the commercial NiMo sulfide catalyst prepared by traditionalmethod.
Keywords/Search Tags:molybdenum phosphide, nickel phosphide, nickel molybdenum phosphide, molybdenum carbide, nickel molybdenum sulfur cluster, hydrodesulfurization, IR spectroscopy
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