Molybdenum sulfide, formation

In the anaerobic digester environment, one would thus expect sulfide reactions to dominate the Mo chemistry since the oxy-anions of the more reduced forms of this metal are relatively unstable (Tucker et al, 1997). For Facility J, total dissolved Mo concentration in the anaerobic digester supernatant was high (47 /rg/l Fig. 3) but the Mo(VI)/(total dissolved Mo) ratio was only 0.15, showing substantive formation of soluble species other than molybdate in the system. The dominant form of molybdenum present in the digester supernatant is unknown and is believed to be molybdenum sulfides. Formation of thio-complexes is also suggested by the ratio... 

Through a co-assembling route, mesostructured lamellar molybdenum sulfides are formed hydrothermally at about 85 °C using cationic surfactant molecules as the templates. The reaction temperature and the pH value of the reaction system are important factors that affect the formation of the mesostructured compounds. The amount of the template and that of the S source are less critical in the synthesis of the compounds. For the three as-synthesized mesostructured materials, the interlayer distance increases linearly with the chain length of the surfactant. Infrared and X-ray photoelectron spectroscopy reveals that the individual inorganic layers for the three compounds are essentially the same both in composition and in structure. The formal oxidation state of the molybdenum in the materials is +4 whereas there exist S2 anions and a small amount of (S-S)2 ligands in the mesostructures. The successful synthesis of MoS-L materials indicates that mesostructured compounds can be extended to transition metal sulfides which may exhibit physico-chemical properties more diverse than non-transition metal sulfides because of the ease of the valence variation for a transition metal. 

Mononuclear Mov complexes with sterically hindered monodentate thiolato ligands are of interest as models for special molybdenum enzymes (the Mo oxidases). Here dimer formation via thiolato bridges and sulfide formation by C—S bond cleavage do not occur. Such a ligand is TIPTH. The complex [Mo(CO)2(TIPT)3) (14), with essentially trigonal prismatic coordination about Mo and trans CO groups in the axial sites, can be obtained.91... 

Tribochemical reaction The formation of an iron sulfide tribofilm may be displaced by other surface active elements such as oxygen, where the oxide of the iron heat of formation AHf = -2.82 eV is thermodynamically more stable than the sulfide AHf = -1.04 eV. Using the data from Table 5.11, compare the heat of formation of molybdenum oxide and molybdenum sulfide. 

Mizutani, Y., Imada, Y and Nakajima, K., Formation of Molybdenum Sulfide in Fe-Mo-S Alloys and its Effect on Frictional Property, Proc. JSLE-ASLE Inti. Lub. Conf., Tokyo, (9-11 June, 1975), p. 161. 

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 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. 

Acidity of the support, which accelerates coke formation, is poisoned with alkali addition. The active component, promoted molybdenum sulfide, is active for dehydogenation and also has acid sites, so the general behavior discussed for catalytic reforming is the same, except for reduced activity and complications from heavier molecules. 

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]. 

With MoSx/USY-Na(3.5) and MoSx/NaY(2.8), the coordination number of Mo-Mo is very close to unity (Table 2), suggesting the formation of extremely dispersed molybdenum sulfide clusters, possibly Mo dimer species in line with previous studies [10-13]. The Mo-Mo atomic distance of the cluster is... 

A general explanation cannot be given, which is valid for different catalysts and reactions, even if these are limited to HDS. One of the characteristic examples is the essential difference in the mechanism of catal3dic effect on sulfided noble metals in comparison with that of molybdenum and tungsten-oxide based catalyst, due to large differences in the energy of their sulfide formation. This difference in HDS mechanism is also well seen from the rather different effect of sulfidation on precious metal promoted MoOx, in comparison with CoMoOx, in the initial period of sulfidation. 

The conversion of methanol and ammonia to methylamines is achieved over dehydration catalysts operated in the temperature range 300450°C and 0.12 MPa pressure. The reactions are exothermic, and excess ammonia is used to control the product distribution. The dehydration catalysts are generally promoted Si-Al composites. The promoters include molybdenum sulfide and silver phosphate [68]. In the commercial Leonard process, a gas-phase downflow catalytic reactor operating at about 350°C and 0.62 MPa is used [69]. Recovery of the desired product is achieved throu a series of four distillation and extractive distillation columns. Unwanted product is recycled, suppressing further formation of the undesired component in the reactor. A very small amount of methanol is lost to CO and H2, and yields from the commercial process based on methanol and anunonia are >97% [70]. 

---