Oxide precursors, sulfidation

The performance of a supported metal or metal sulfide catalyst depends on the details of its preparation and pretreatraent. For petroleum refining applications, these catalysts are activated by reduction and/or sulfidation of an oxide precursor. The amount of the catalytic component converted to the active ase cind the dispersion of the active component are important factors in determining the catalytic performance of these materials. This investigation examines the process of reduction and sulfidation on unsupported 00 04 and silica-supported CO3O4 catalysts with different C03O4 dispersions. The C03O4 particle sizes were determined with electron microscopy. X-ray diffraction (XRD), emd... 

Methyl-2,4,6-triisopropyl-l,3,5-dioxaphosphorinanes (27) have been obtained by the addition of methyl iodide to (26) (791ZV1863). The alkylation did not stop at the first stage. Together with the product of the addition of one molecule of methyl iodide, a product of dialkylation (28) was also obtained [Eq. (17)]. The addition proceeds in a nonstereospecific manner. Whereas the precursor substance exists as one stereoisomer, compound (26) is a mixture of two stereoisomers in a ratio of 30 70 (78DOK331). Stereoisomeric oxides and sulfides of (27) have been prepared. 

Nomura, R. Fujii, S. Kanaya, K. Matsuda, H. 1990. Oxygen- or sulfur-containing organoindium compounds for precursors of indium oxide and sulfide thin films. Polyhedron 9 361-366. 

In metamorphosed sedimentary rocks, arsenic tends to occur in oxide and sulfide minerals (Bebout et al., 1999), 69-70. Many metamorphic rocks simply inherit their arsenic from their precursor rocks. That is, unless arsenic-rich metamorphic fluids are introduced, quartzites metamorphosed from low-arsenic quartz-rich sandstones and marbles metamorphosed from low-arsenic limestones should have relatively little arsenic. In contrast, shales often contain more arsenic than sandstones and limestones (Table 3.23). Therefore, slates and phyllites that form from the metamorphism of shales should inherit at least some of the arsenic (Table 3.24). 

Prins summarizes advances in understanding of the reactions in catalytic hydrodenitrogenation (HDN), which is important in hydroprocessing of fossil fuels. Hydroprocessing is the largest application in industrial catalysis based on the amount of material processed. The chapter addresses the structures of the oxide precursors and the active sulfided forms of catalysts such as Ni-promoted Mo or W on alumina as well as the catalytically active sites. Reaction networks, kinetics, and mechanisms (particularly of C-N bond rupture) in HDN of aliphatic, aromatic, and polycyclic compounds are considered, with an evaluation of the effects of competitive adsorption in mixtures. Phosphate and fluorine promotion enhance the HDN activity of catalysts explanations for the effect of phosphate are summarized, but the function of fluorine remains to be understood. An account of HDN on various metal sulfides and on metals, metal carbides, and metal nitrides concludes this chapter. 

It is also possible to take advantage of studies dealing with the preparation of supported oxide precursors (namely, oxides to be further activated to produce active metals or sulfides by reduction or sulfidation, respectively). Although there is limited information in this field, some scattered information has been published, essentially for M0O3 and V2O5. Infrared and Raman spectroscopies have provided data concerning various steps in the transformation of precursor salts to oxides. 

Except for a part of the recent attempts to avoid in situ sulfidation, the activation of traditional hydro-treating catalysts always corresponds to the reaction of hydrogen and sulfur-containing compounds with the oxide precursor. Innumerable recipes are proposed for use in industry and have been described in literature. One article, among many, gives a still valuable overview of the possible procedures [128]. 

Non-aqueous synthetic methods have recently been used to assemble mesoporous transition metal oxides and sulfides. This approach may afford greater control over the condensation-polymerization chemistry of precursor species and lead to enhanced surface area materials and well ordered structures [38, 39], For the first time, a rational synthesis of mesostructured metal germanium sulfides from the co-assembly of adamantanoid [Ge4S ()]4 cluster precursors was reported [38], Formamide was used as a solvent to co-assemble surfactant and adamantanoid clusters, while M2+/1+ transition metal ions were used to link the clusters (see Fig. 2.2). This produced exceptionally well-ordered mesostructured metal germanium sulfide materials, which could find application in detoxification of heavy metals, sensing of sulfurous vapors and the formation of semiconductor quantum anti-dot devices. 

Theories and principles of the characterization techniques are not described here. For consistenc), all the catatysts described in this review are referred to with the same nomenclature, although a different nomenclature is sometimes used in the cited publications. Each catalyst component (element) separated by the symbol indicates the sequence of its introduction into the catalyst formulation from right to left. Those separated by the symbol 7 between right and left belong to the support material and the elements on the support, respectively. For example, NiMo-P/Al refers to a catalyst prepared such that the phosphorus-containing precursor is loaded on the alumina support first, followed by nickel and molybdenum, which are introduced simultaneously. CoMo/Al — P refers to a catalyst in which cobalt and molybdenum are introduced simultaneously onto an alumina support doped with phosphorus-containing species. Each element may represent its oxide or sulfide forms. In all cases, A1 refers to the alumina-based support or to its hydroxide precursor. 

Sulfoxides are readily available via oxidation of sulfides with peroxycarboxylic acids (e.g., mCPBA, 1.0 eq) or sodium or potassium periodate. The sulfides themselves can be prepared by nucleophilic displacement of tosylate or mesylate esters with sodium alkyl- or phenylsulfides. In the example shown below, the sulfoxide approach worked better than direct E2 elimination of the mesylate precursor. ... 

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. 

This is a very useful route for the preparation of phosphines, especially chiral phosphines. Tertiary phosphine oxides (and sulfides) and phosphonium salts are often precursors of choice in these reduction procedures. The following sections highlight reagents and reaction conditions in forthcoming sections further examples will be given. 

The change of composition of mesoporous materials can be done by direct synthesis and post-synthesis modification. Now, the composition of mesoporous materials can be extended to nonsilica oxides, phosphates, sulfides, even metals. The study of nonsilica mesoporous materials started much later than that for silica-based materials. The main reasons include the hydrolysis and condensation reactions of transition metal precursors is difficult to control the inorganic wall easily crystallizes and results in the loss of mesostructures the synthetic procedure is difficult to repeat. 

Additionally, the s mthesis route is able to produce hydrosulfides and sulfides from many different hydroxide and oxide precursors. 

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