Transition metal sulphides

Kinetic observations for decomposition of some representative transition metal sulphides are summarized in Table 13. Several instances of an advancing interface [contracting volume, eqn. (7), n = 3] rate process have been identified and the rate may be diminished by the presence of sulphur. Diffusion control is, however, believed to be important in the reactions of two lower sulphides (Ni0.9sS. [687] and Cu1-8S [688]). These solids have attracted particular interest since both are commercially valuable ores and pyrolysis constitutes one possible initial step in metal extraction. 

Summary of kinetic characteristics for decompositions of some transition metal sulphides 

Reactant Product Kinetic characteristics a range considered Temperature range (K) E (kJ mole 1) Ref. 

Although not strictly included within the scope of the present review, decompositions have been considered in the context of related rate processes including sulphide oxidations, sulphidation of oxides and/or metals and diffusion in sulphide phases [689], 

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Mills AM, Ruck M (2005) Ce53Fe12S9oX3 (X = Cl, Br, I) The first rare-earth transition-metal sulphide halides. Inorg Chem 45 5172-5178... 

Partially Crystalline Transition Metal Sulphide Catalysts. Chiannelli and coworkers (6, 7, 8) have shown how, by precipitation of metal thio-molybdates from solution and subsequent mild heat-treatment many selective and active hydrodesulphurization catalysts may be produced. We have shown (18) recently that molybdenum sulphide formed in this way is both structurally and compositionally heterogeneous. XRES, which yields directly the variation in Mo/S ratio shows up the compositional nonuniformity of typical preparations and HREM images coupled to SAED (see Figure 2) exhibit considerable spatial variation, there being amorphous regions at one extreme and highly crystalline (18, 19) MoS at the other. 

Correlations between catalytic activity and a variety of bulk properties of semiconductors have been reported (i) the average band gap of III-V and II-VI semiconductors and activity towards hydrogenation of isopropanol (ii) enthalpy of oxides and their activity towards oxidation of propylene and (iii) number of d-electrons (and crystal field stabilization energy) or 3rf-metal oxides and their activity towards N2O decomposition. The last correlation, due to Dowden (1972), is important since it provides a connection between heterogeneous catalysis and coordination chemistry of transition-metal compounds. A correlation between the catalytic activity of transition-metal sulphides towards hydrodesulphurization of aromatic compounds and the position of the transition metal in the periodic table has been made by Whittingham ... 

Figure 8.19 Catalytic activity of transition-metal sulphides for hydrodesulphurization of dibenzothiophene. (After Whittingham Chianelli,...

Transitional-metal sulphides and selenides with pyrite structure of the form MS2 and MSe2 Ni(Sej —xSx)2... 

CATALYTIC PROPERTIES OF TRANSITION METAL SULPHIDES FOR THE DEHYDROGENATION OF SULPHUR CONTAINING MOLECULES. 

The catalytic properties of unsupported transition metal sulphides have been examined for the reaction of dehydrogenation of tetrahydrothiophene. This study has shown that a selectivity higher than 90% for thiophene formation can be obtained for the most active catalysts, essentially the second row sulphide catalysts. The comparison between the catalytic activities in both dehydrogenation of tetrahydrothiophene and... 

Transition metal sulphides are able to catalyze a very large number of reactions. The most important utilization concerns catalytic hydrotreating, but many others can be foreseen due to the resistance of these catalysts towards sulphur. For example, recent studies have demonstrated the interest of such catalysts for the selective conversion of carbon monoxide into hydrocarbons [1] or alcohols [2]. Until now, only few papers and patents report on the utilization of sulphides for fine chemical applications [3-6]. Nevertheless, this type of solids fits well to catalyze the reactions dealing with sulphur containing molecules. 

The objective of the present work is to classify the catalytic performances of unsupported transition metal sulphides (TMS) for these different reactions dehydrogenation of a sulphur containing molecule without sulphur elimination, hydrodesulphurization and hydrogenation. 

Crystalline phases, surface areas (Sggip), specific and intrinsic activities of transition metal sulphides... 

The catalytic activities of transition metal sulphides were classified in the DHN of THT, the HDS of thiophene and the HN of BP. The results clearly evidence strong similarities between the activities of the most active catalysts in the three reactions, which implies that the catalytic sites involved in each of these reactions are comparable. 

Thermodynamic calculations suggest that the maximum conversion efficiencies for the first step will be of the order of 90% for most transition metal sulphides (4). 

T. Weber, R. Piins, R. A. Van Santen (Eds), Transition Metal Sulphides Chemistry and Catalysis, NA TO ASI Series, Springer, 1998. 

Raybaud P., Hafiier J., Kresse G., and Toulhoat H., Ab initio density ftmctional studies of transition-metal sulphides II. Electronic structure, J. Phys. Condens. Matter 9 (1997) pp. 11107-11146. 

F. Hornung, M. Krejcik, J. Fiedler, S. Zalis in Transition Metal Sulphides—Chemistry and Catalysis, NATO ASI Series, (T. Weber, Ed.) Kluwer Academic Publishers, Dordrecht, 1998, p. 37,... 

Conversion to sulphur compounds is a means of recycling sulphur and hydrogen sulphide produced in petroleum refining. The compound COS has been synthesized from CO + S over CaS + BaS and CO + H2S over transition metal sulphides (443-653 K). The CO/H2S reaction is also a means of producing hydrogen. The initial rate of hydrogen formation was given by... 

In reactions of sulphur with hydrogen and hydrocarbons over transition-metal sulphides rate constants decreased in the order H>C2H4 >C2Hg. The rate-determining step for the hydrocarbons, as for hydrogen (cf. Section 2), was cleavage of the metal-sulphur bond. 

A number of important structure types are found in transition-metal sulphides which have no counterparts among oxide structures, notably the various layer structures and the pyrites, marcasite, and NiAs structures. Further, many sulphides, particularly of the transition metals, behave like alloys, the resemblance being shown by their formulae (in which the elements do not exhibit their normal chemical valences, as in 0983, Pd4S, TiSa), their variable composition, and their physical properties-metallic lustre, reflectivity, and conductivity. The crystal structures of many transition-metal sulphides show that in addition to M-S bonds there are metal-metal bonds as, for example, in monosulphides with the NiAs structure (see later), in chromium sulphides, and in many sub-sulphides such as Hf2S,... 

We have noted one difference between complex oxides and sulphides, namely, the compounds of class (c) have no counterpart among oxy-compounds. A second difference is that sulphides other than those of the most electropositive elements show more resemblance to metals than do oxides. Metal-metal bonding occurs only rarely in simple oxides whereas it is more evident in many transition-metal sulphides. In many complex sulphides of class (c), as indeed in simple sulphides such as those of Cu, it is not possible to interpret the atomic arrangements and bond lengths in terms of normal valeilce states of the metals, suggesting a partial transition to metallic bonding, as is also indicated by the physical properties of many of these compounds. 

Th. Weber, R. Prins and R.A. van Santen, "Transition Metal Sulphides - Chemistry and Catalysis", Kluwer (Eds.), Dordrecht, 1998. 

Cody, G.D., Boctor, N.Z., Brandes, J.A., Filley, T.R., Hazen, R.M., and Yoder, H.S., 2004. Assaying the catalytic potential of transition metal sulphides for abiotic carbon fixation. Geochim. Cosmochim. Acta, 68, 2185-96. 

Studies have continued on the intercalation of the alkaline-earth metals into lattices of the transition-metal sulphides. Calcium and strontium are intercalated into M0S2 from liquid ammonia solution. X-Ray data reveal a lowering of the crystal symmetry of the sulphide and an increase in the complexity of the structure on intercalation. The intercalation compounds begin to superconduct at ca 4 K (for Ca) and 5.6 K (for Sr), and they show considerable anisotropy with respect to the critical magnetic field. Calcium in liquid ammonia also intercalates with TiS2- Two Ca,TiS2 phases have been identified. The limits of the first are 0.03 0.50, for which a relationship between x and cell parameters a and c... 

Angelici, R.J. in Weber, T., Ed., Transition Metal Sulphides, Kluwer Academic, Nether-land, 1998, pp. 89. 

In contrast to the sulphides of most of the transition metals, sulphides of the refractory metals have quite tight stoichiometry, similar to Cr203, although, in the cases of the refractory-metal sulfides and oxides, the defects appear on the anion sub-lattice. Figure 6.1 compares the rates of oxidation and sulphidation for several of the transition and refractory metals. The low rates of sulphidation of the refractory metals are thought to be due to the low concentrations of defects in the sulphide structures. 

Toulhoat, H., Raybaud, P. Eds. Catalysis by Transition Metal Sulphides Edition Technip Paris, France, 2013. 

Weber, T, Prins, R, van Santen, R. A., Eds. Transition Metal Sulphides, Chemistry and Catalysis, NATO ASI Series Kluwen Dordrecht, 1998. 

True nanotubes built from layered inorganic materials have extraordinary mechanical properties and are already used in many applications. Especially the transition-metal sulphides M0S2 and WS2 have been studied to a large extent, and their most prominent application is as lubricants. Some systems have been investigated with respect to their ability of hydrogen storage and battery applicability. The synthetic routes for these systems are already well established paths, e.g. via... 

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