Molybdenum sulfide, decomposition

Of the many molybdenum sulfides which have been reported, only MoS, M0S2 and M02S3 are well established. A hydrated form of the trisulfide of somewhat variable composition is precipitated from aqueous molybdate solutions by H2S in classical analytical separations of molybdenum, but it is best prepared by thermal decomposition of the thiomolybdate, (NH4)2MoS4. MoS is formed by heating the calculated amounts of Mo and S in an evacuated tube. The black M0S2, however, is the most stable sulfide and, besides being the principal ore of Mo,... 

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... 

Hexacarbonyl molybdenum Mo(CO)6 was successfully used to prepare intrazeolite molybdenum sulfide clusters in the cavities of NaY (CVD technique) [4,5,7,8]. The decomposition and sulfidation of Mo(CO)e encaged in NaY were extensively studied by Okamoto et al. [7-11] by means of temperature programmed decomposition (TPDE), XPS, and XAFS techniques. It has been claimed that the structure of molybdenum sulfides is described as molybdenum dinuclear sulfide clusters M02S4. de Bont et al. [12] supported the formation of molybdenum sulfide dimer species. The extremely high dispersion of molybdenum sulfide clusters prepared fi"om Mo(CO)6 was also suggested by an NO adsorption capacity much hi er than those of other conventional catalyst systems such as M0S2/AI2O3 [9]. 

Olivers T, Lau C (1987) The thermal decomposition of hydrogen sulfide over vanadium and molybdenum sulfides and mixed sulfide catalysts in quartz and thermal diffusion column reactors. Int J Hydrogen Energy 12(4) 235-243... 

Chevrel phases are frequently considered to be reduced molybdenum sulfides because of the low molybdenum oxidation state relative to M0S2. These compounds are also stable under HDS conditions. The low oxidation states are maintained and no decomposition or transformation to other sulfides has been detected for most compounds (61). Chevrel phases usually are obtained through solid-state syntheses at high temperatures (1000-1300°C) by direct combination of the elements or by direct insertion of ternary metal into the binary MogSg... 

Catalysts used for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of heavy oil fractions are largely based on alumina-supported molybdenum or tungsten to which cobalt or nickel is added as a promoter [11]. As the catalysts are active in the sulfided state, activation is carried out by treating the oxidic catalyst precursor in a mixture of H2S and H2 (or by exposing the catalyst to the sulfur-containing feed). The function of hydrogen is to prevent the decomposition of the relatively unstable H2S to elemental sulfur, which would otherwise accumulate on the surface of the... 

Peters (5) Has reviewed the leaching of copper, nickel, zinc, lead and molybdenum concentrates in terms of the thermodynamic stability of the sulfide minerals of these metals. Process developments associated with the most favorable decomposition paths are considered. 

Although thermodynamically possible, the slower rate of substitution of the tungsten(VI) species results in the formation of only a small amount of the corresponding thiotungstate ion, provided that the conditioning period with sulfide ion is controlled. Molybdenum trisulfide is then quantitatively precipitated by the decomposition of the thio salt by the slow addition of sulfuric acid to a pH value of between 2 and 3 ... 

To a suspension of a molybdenum-aluminum alloy (1 1 36.5 g) in boiling water (300 ml) is slowly added a solution of sulfuric acid (130 g) in water (100 ml). The suspension is stirred for 4 h at 100°. The decomposition product is washed with water until free from acid and then placed in methanol. The mixture is then saturated with hydrogen sulfide, and the suspension is set aside for two weeks. The product is then washed again with methanol. The resulting catalyst is kept under methanol. 

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