Transition-metal sulfide catalysts preparation

The importance of edge planes also arises in the industrially important promoted transition metal sulfide catalyst systems. It has been known for many years that the presence of a second metal such as Co or Ni to a M0S2 or WS2 catalyst leads to promotion (an increase in activity for HDS or hydrogenation in excess of the activity of the individual components) ( ). Promotion effects can easily be observed in supported or unsupported catalysts. The supported catalysts are currently the most important industrial catalysts, but the unsupported catalysts are easier to characterize and study. Unsupported, promoted catalysts have been prepared by many different methods, but one convenient way of preparing these catalysts is by applying the nonaqueous precipitation method described above. For example, for Co/Mo, appropriate mixtures of C0CI2 MoCl are reacted with Li2S in ethyl acetate ... 

The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

Malz, Jr. and Greenfield studied the preparation of tertiary amines by reductive alkylation of aliphatic secondary amines with ketones, using platinum metals and their sulfides as catalysts.40 Excellent yields of tertiary amines were obtained with unhindered ketones, such as cyclohexanone and acetone, and relatively unhindered secondary amines. In this study, 5% Pd-C and various transition metal sulfides were compared in the reductive alkylation of dibutylamine with cyclohexanone. By using the reaction conditions suitable to each catalyst, excellent yields of tertiary amines were obtained, as shown in Table 6.5. Approximately 5-15% of the excess cyclohex-... 

The Transition Metal Sulfides are a group of solids which form the basis for an extremely useful class of industrial hydrotreating and hydroprocessing catalysts. Solid state chemistry plays an important role in understanding and controlling the catalytic properties of these sulfide catalysts. This report discusses the preparation of sulfide catalysts, the role of disorder and anisotropy in governing catalytic properties, and the role of structure in the promotion of molybdenum disulfide by cobalt. 

The catalysts described above were prepared via low temperature precipitation from non-aqueous solution (J). This technique involves the precipitation of the transition metal sulfide from a non-aqueous solvent such as ethyl acetate by dissolving the appropriate transition metal halide in the solvent and reacting it metathetically with a sulfiding agent such as lithium sulfide to precipitate the insoluble sulfide for example ... 

The effect of crystal structure may be investigated by preparing catalysts, as described above, at various temperatures which assures a set of catalysts having variable surface areas, pore size distributions, and crystallinity. Measuring the catalytic activity as a function of these physical properties will help to define the role of crystal structure for the particular transition metal sulfide. In general, the HDS is poorly correlated to N2 BET surface area. This non-correlation can be most easily seen by preparing a... 

Solid state chemistry plays an important role in the catalysis by Transition Metal Sulfides however, it is a role that is somewhat different than the role usually assigned to solid state chemistry in catalysis. In catalysis, by sulfides, the chemistry of ternary phases is not now important and thus, the usual role of solid state chemistry in preparing ternary phases and systematically studying the effect on catalytic properties through variation of the composition of these ternary phases is absent. Nevertheless, preparation of the Transition Metal Sulfides is crucial in controlling the properties of the catalysts. Low temperature solid state preparations are the key to obtaining good catalysts in reasonable surface area for catalytic measurements. 

Aromatic organosulfur compounds such as thiophenes, benzothiophenes and dibenzothiophenes are frequently contained in fossil oil and their sulfur atoms are generally difficult to remove in HDS process [106], In the industrial HDS process, Mo/Co/S or Ni/Mo/S heterogeneous catalysts supported on alumina are widely employed. In order to obtain ideas to develop more efficient catalysts as well as to shed some light on their mechanisms at a molecular level, transition metal complex-mediated cleavages of C-S bond are extensively studied. On the other hand, thiiranes and thietanes are frequently employed for preparation of transition metal sulfides, in which their C-S bonds are smoothly cleaved. In this section, the C-S bond cleavages of thiophene derivatives, thiiranes, thietanes, vinylic sulfides, allylic sulfides, thiols and dithioacetals are overviewed. 

An elegant and efficient way for preparation of sulfonium ylides under mild conditions is the so-called Doyle-Kirmse reaction [25,26], which involves transition metal catalyzed decomposition of diazo compounds (usually a-diazocarbonyls) in the presence of sulfides. For the catalytic generation of matallocarbenes from diazo compounds, copper catalysts have traditionally been employed. More recently, rhodium and ruthenium compoimds were reported to be efficient catalysts, especially for the generation of sulfoniiun ylides [27-29]. 

Transition Metal Salts and Oxides on Alumina. Transition metal salts, particularly chlorides and nitrates, are frequently used as starting materials for the preparation of supported transition metal oxides or supported precursors for supported metal catalysts. Also, many catalytic materials, particularly supported molybdenum and tungsten oxide and sulfide catalysts, contain transition metal ions, namely Co, Ni , and Fe " as promoters. Thus, it is interesting to study the spreading and wetting behavior of salts of these transition metals and of their oxides. This is of particular importance for promoted catalyst materials, since in practice the incorporation of the active phase and the promoter should be possible in one step for economic reasons. 

Studies performed in previous years (ref.3-5) over molybdenum loaded zeolites in HDS reaction showed that reactivity of these catalysts depends on the type of zeolite used, concentration of transition metal and the way of preparation. However, preparation of molybdenum based catalysts applying ammonium heptamolybdate usually results in low dispersion of molybdenum sulfides and relatively low activity. Recent studies showed that saturation of Y-zeolites with molybdenum carbonyl can produce catalysts with high molybdenum dispersion (ref.6, 7). Subsequent sulfidation of these catalysts leads toward highly dispersed, supported sulfided molybdenum species (ref. 8,9) exhibiting high reactivity in HDS and water-gas shift reaction (ref. 9,10). 

Shu and Oyama have recently proposed a new type of hydrotreating catalytst transition metal phosphides supported on carbon [97], and compared their behavior in the deep HDS of 4,6-DMDBT with that of the silica-supported counterparts and a commercial alumina-supported Ni-Mo sulfide hydrotreating catalyst. The carbon-supported catalysts were prepared by temperature-programmed reduction of the corresponding phosphates, and the activity was studied under simulated industrial conditions of 613 K and 3.1 MPa with a model liquid feed coutaiu-ing 500-ppm sulfur as 4,6-DMDBT, 3000-ppm sulfur as dimethyl disulfide, aud 200-ppm nitrogen as quinoline. The Ni2P/C catalyst showed an excellent performance in HDS and HDN, and it was also the best for sulfur removal from... 

The higher the active surface area of the catalyst, the greater the number of product molecules produced per unit time. Therefore, much of the art and science of catalyst preparation deals with high-surface-area materials. Usually materials with 100- to 400-m /g surface area are prepared from alumina, silica, or carbon and more recently other oxides (Mg, Zr, Ti, V oxides), phosphates, sulfides, or carbonates have been used. These are prepared in such a way that they are often crystalline with well-defined microstructures and behave as active components of the catalyst system in spite of their accepted name supports. Transition-metal ions or atoms are then deposited in the micropores, which are then heated and reduced to produce small metal particles 10-10" A in size with virtually all the atoms located on the surface... 

Iron and its compounds (carbide, nitride), as well as ruthenium, cobalt, rhodium, and molybdenum compounds (sulfide, carbide), are used most frequently to produce high-molecular-weight hydrocarbons. Iron can be prepared as a high-surface-area catalyst (==300 m /g) even without using a microporous oxide support. 7-AI2O3, Ti02, and silica are frequently used as supports of the dispersed transition-metal particles. Recently zeolites, as well as thorium oxide and lanthanum oxide, have... 

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