Molybdenum sulfide hydrogenation

Although supported Pd catalysts have been the most extensively studied for butadiene hydrogenation, a number of other catalysts have also been the object of research studies. Some examples are Pd film catalysts, molybdenum sulfide, metal catalysts containing Fe, Co, Ni, Ru, Rh, Os, Ir, Pt, Cu, MgO, HCo(CN) on supports, and LaCoC Perovskite. There are many others (79—85). Studies on the weU-characteri2ed Mo(II) monomer and Mo(II) dimer on siUca carrier catalysts have shown wide variations not only in catalyst performance, but also of activation energies (86). 

Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions. 

Moreau, C. Bekakra, L. Olive, J. L., and Geneste, P., Hydrodenitrogenation of Quinoline and Phenanthridine in the Presence of 2, 6-Diethylaniline and Hydrogen-Sulfide Over Molybdenum and Nickel-Molybdenum Sulfides Supported on Zirconia, Titania, Nickel-Aluminates and Magnesium-Aluminates. Bulletin Des Societes Chimiques Beiges, 1991. 100(11-12) pp. 841-847. 

The concentrated molybdenite ore is then roasted in air, converting molybdenum sulfide to molybdenum trioxide M0O3. This is harvested in high purity by sublimation. An alternative is to leach molybdenite concentrate with dilute ammonia solution, which converts the metal to ammonium molybdate, (NH4)2Mo04. Molybdenum trioxide or ammonium molybdate product is then heated with hydrogen at elevated temperatures from 500 to 1,150°C in a furnace to produce molybdenum powder. 

The mechanism of the catalyst activation by sulfur is not understood. The amount of sulfur compounds necessary to maintain or increase the catalyst activity depends in some cases on the stability of the heavy-metal sulfide component of the catalyst. Thus molybdenum sulfide seems to require a higher hydrogen sulfide concentration than tungsten sulfide. However, some catalysts that do not contain elements that can form sulfides under reaction conditions also showed an increased activity when sulfur compounds were added to the feed. Hydrogen sulfide in many cases decreases the catalyst sensitivity to nitrogen compounds and thus causes an activity increase. Sufficient data for pure compounds are not available to permit segregation of these effects. 

Molybdenum sesquisulfide, Mo2S3, is the lowest sulfide in the Mo-S system. Contrary to previous claims64, it has now been established65 that Mo2S3, and not MoS2, is in equilibrium with molybdenum metal and sulfur vapor in the vicinity of 1100 °C.The presence of Mo2S3 has also been established in equilibrium studies in the molybdenum-sulfur-hydrogen system between 850 and 1200 °C16. ... 

Work was carried out in this laboratory to reproduce these reactions7. Attempts to prepare Mo02S did not yield a simple molybdenum oxysulfide or a molybdenum sulfide, but a mixture of unidentifiable products. The reaction of MoS2 with water vapor yielded neither hydrogen nor hydrogen sulfide. The thermal decomposition of... 

Huang, C.S., K.C. Wang, and J. H.W. Haynes, Hydrogenation of Phenanthrene Over a Commercial Cobalt Molybdenum Sulfide Catalyst Under Severe Reaction Conditions, in Liquid Fuels from Coal, eds., Academic Press, 1977. 

In connection with the research on destructive hydrogenation at the Institute of High Pressures, Maslyanskii (224) passed benzene at 475° under 200 atm. hydrogen over molybdenum oxide (1 mole CeH6 16 moles Ha) to produce 58% methylcyclopentane, 14% cyclohexane, 8% 2-methyl-pentane, 5% n-hexane, and 8% unreacted. Over molybdenum sulfide the product distribution was similar. The preparation of these catalysts was described by him in 1940 (223). Isomerization and other conversions accompanying destructive hydrogenation were also pointed out by Prokopets and by others (257,311,314). 

Hall and Cawley hydrogenated biphenyl over pelleted molybdenum sulfide at 350°C and 20-30 MPa H2, and obtained cyclohexylbenzene, benzene and cyclohexane, and dicyclohexyl, along with their isomerides.58... 

Thiophene was also hydrogenated to tetrahydrothiophene over rhenium heptasulfide (Re2S7) at 230-260°C246 or rhenium heptaselenide (Re2Se7) at 250°C and at pressures greater than 30 MPa H2 (eq. 12.129),247 without accompanying hydrogenolysis of the carbon-sulfur bond that occurred extensively over molybdenum sulfide.246... 

The heterocyclic ring of benzoxazoles (156) can be cleaved by exposure to diborane giving borazoles (157 possibly as shown in Scheme 8). Treatment of these products with hydrochloric acid leads to the formation of 2-aminophenols (158). Catalytic hydrogenation of the parent compound (156 R = H) over molybdenum sulfide has a similar end result although, since the conditions of the reaction are quite severe, phenol and 2-toluidine can form as by-products. ... 

The simplest networks are one-dimensional a-networks which may be composed of secondary amides, primary amide dimers or nucleophospholipids. In chapter 5, such structures were discussed as micellar rods and tubules in bulk aqueous solutions. Two-dimensional materials such as copper oxide superconductors, molybdenum sulfide lubricants and intercalated graphites are mostly inorganic. The anisotropic properties are a result of covalent bonds in two dimensions and weak interactions in the third dimension. One may, however, also envision strong hydrogen-bond interactions within an organic layer, whereas adjacent layers are held together only by van de Waals interactions. The two-dimensional, or p-network may form spontaneously from an... 

Iron-chromium oxide catalysts, reduced with hydrogen-containing in the conversion plants, permit reactions temperatures of 350 to 380°C (high temperature conversion), the carbon monoxide content in the reaction gas is thereby reduced to ca. 3 to 4% by volume. Since, these catalysts are sensitive to impurities, cobalt- and molybdenum-(sulfide)-containing catalysts are used for gas mixtures with high sulfur contents. With copper oxide/zinc oxide catalysts the reaction proceeds at 200 to 250°C (low temperature conversion) and carbon monoxide contents of below 0.3% by volume are attained. This catalyst, in contrast to the iron oxide/chromium oxide high temperature conversion catalyst, is, however, very sensitive to sulfur compounds, which must be present in concentrations of less than 0.1 ppm. 

The activity and selectivity of 12.5% M0/AI2O3 nitrided at various temperatures for the hydrodesulfurization (HDS) of dibenzothiophene and the effect of re-treatment of NH3 on dibenzothiophene HDS were studied. The nitrided catalyst was significantly more active toward the scission of the C-S bond from dibenzothiophene with hydrogenation of dibenzothiophene. The sulfur species accumulated on the surface of the nitrided M0/AI2O3 catalysts by replacement of nitrogen species after reaction was analyzed by XPS measurement. The formation of molybdenum sulfide during the HDS dibenzothiophene led to a decrease in the activity of the nitrided catalyst, which approached that of the sulfided catalyst. 

In conclusion, an extensive literature is available on the reaction networks that are thought to operate in HD,S of various types of thiophenic molecules besides the great advances that have been made in direct studies on molybdenum sulfides and related catalysts, this is another area in which organometallic chemistry has made an impressive contribution to HD,S catalysis, as a number of reaction pathways and mechanisms for the hydrogenation and hydrogenolysis of thiophenes on metal complexes in solution has been well established with the aid of a variety of physical techniques. 

M. Lacroix, H. Jobic, C. Dumonteil, P. Afanasiev, M. Breysse S. Kasztelan (1996). Stud. Surf. Sci. Catal. Part A B., 101, 117-126, Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions. 

Tin is left in solution if molybdenum sulfide is precipitated in the presence of oxalic acid by hydrogen sulfide in a pressure bottle. In ores if outsitcrite jH present, it. may Is left with the insoluble residue hy dissolving the molybdenum with an add. 

Keywords Sepiolite, Molybdenum Sulfide Oxygen Chemisorption, Hydordesulfurization, Hydrogenation... 

Results presented in Table 1 and those obtained during hydrogenation of cyclopentene indicate that at the experimental conditions supported molybdenum sulfide is rather inactive in hydrogenation. For this reasons the description of the results concerning hydrogenation of cyclopentene will focus on molybdenum free catalysts. 

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