Sulfides microporous metal

In the late 1980s Bedard et al. reported the discovery of microporous metal sulfides, based on germanium (IV) and Sn (IV) sulfide frameworks [52]. 

Bedard, R.L, Wilson, S.T., Vail, L.D., Bennett, J.M., and Flanigen, E.M. (1989) The next generation synthesis, characterization, and structure of metal sulfide-based microporous solids, in Zeolites Facts, Figures, Future (eds... 

The radius in the micropore and hence the constricted diffusivity in the micropore are functions of position in the micropore x, location of the microsphere in the pellet ra, and time due to the deposition of the metal sulfide. The micropore radius R at time t is determined by the deposition... 

R. Bedard, S. T. Wilson, L. D. Vail, J. M. Bennett, and E. M. Flanigen, The Next Generation Synthesis, Characterization and Structure of Metal Sulfide-based Microporous Solids. Stud. Surf. Sci. Catal., 1989, 49, 375-387. 

With respect to the metal recovery for reuse, the study of Lee et al deserves attention. These authors used the oil-soluble compounds of Mo, W, Ni and Co as the precursors for dispersed metal-sulfide catalysts. For single metals, the best performance was observed for the Mo catalyst. The combination of Co -1- Mo gave the most active catalyst for HDS, whereas Ni + Mo was best for HCR. In this study, the fixed bed of extmdates made either of the microporous AC or of y-Al203 was placed downstream of the reaction zone with the aim to remove metals from the product streams. For the former, the overall conversion increased with time on stream. This was attributed to the accumulation of metals on AC. Thus, the metal-deposited AC exhibited catalytic activity. It was noted that the efficiency of the metal removal using the AC extrudates was rather high. It is believed that there are a number of methods that are suitable for the recovery of metals that were trapped by the AC. For example, combustion of the AC will leave behind ash with a high concentration of metals. In this study, an AR containing 26 ppm of V + Ni was used as the feed. 

Lithium batteries using solid cathodes typically use a thin lithium-metal foil or disk as the anode a transition metal oxide, metal sulfide, or a fluoride as the cathode and an organic electrolyte. The cathode material is either coated onto a foil substrate (often aluminum) or embedded into an expanded metal or perforated metal substrate. The anode and cathode are separated by a microporous plastic membrane separator, usually polyethylene and/or polypropylene. 

In general, most of doped or nanosized metal sulfide solid solutions could be synthesized by soft chemistry routes however, their low surface areas seriously limit the enhancements in activity. The preparation of high surface area samples with mesoporous stmctures and exposed surface sites is still a great challenge and highly desired [161]. At this end, research efforts should be directed at constructing 2D nanosheets and nanoporous structures of metal sulfide solid solutions [158,162-164]. In addition, the surface areas of metal sulfide solid solutions can be enhanced by loading them into the porous materials such as microporous and mesoporous silicas [165-167]. 

The microporous sulfides are synthesized hydrothermally in the presence of alkylammonium templating agents. The GeS4-based composihons include one or more framework-incorporated metals Mn, Fe, Co, Ni, Cu, Zn, Cd and Ga. Over a dozen novel shuctures were reported which have no analogs in the microporous oxides. Ozin et al. have extended this work to a large number of microporous sulfides and selerhdes [53]. It should be noted that the microporous sulfides and selenides are prone to shucture collapse upon calcinahon to remove the template species. 

Later, Yaghi et al.[32] proposed an alternative route for the synthesis of these sulfides, in which crystals were obtained from the diffusion of an aqueous solution of the 3d metal into a solution of R-Ge4S10 complex at room temperature. In 1997, Martin and Greenwood133 successfully prepared a new class of microporous metal chlorides, named CZX-n, under solvothermal conditions (160°C) in benzene solution. The framework of CZX-1 is isostructural with the aluminosilicate sodalite (SOD), while CZX-2... 

The history of mesoporous material synthesis is unintentionally or intentionally duplicating the development of zeolites and microporous molecular sieve. It starts from silicate and aluminosilicate, through heteroatom substitution, to other oxide compounds and sulfides. It is worth mentioning that many unavailable compositions for zeolite (e.g., certain transition metal oxides, even pure metals and carbon) can be made in mesoporous material form. 

In this chapter we describe some applications of inelastic neutron scattering in surface chemistry, more particularly in studies of catalysts and adsorbed species [1]. Our emphasis will be on the spectroscopy. The subject matter is arranged broadly according to the type of catalyst metals ( 7.3), oxides ( 7.4), zeolites and microporous materials ( 7.5) and sulfides ( 7.6) and, within each group, according to the reactant molecules. We start ( 7.1) with a general discussion of surface vibrations. 

Most heterogeneous catalysts exist in the form of microporous solids. The catalysts are usually produced in the shape of spheres, cylinders, or monoliths, such as those shown in Figure 1. The internal surface area is typically 10-10 m /g. Catalysis occurs either on the surface of the microporous solid, as in the case of zeolites, or on the surface of microdomains of active material dispersed inside the microporous solid, as in supported metals, oxides, sulfides, etc. In either case, the high internal surface area of the microporous solid is used to obtain a high concentration per unit volume of catalytically active centers. 

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... 

Zeolites form another class of materials useful for fundamental studies . As mentioned earlier, zeolites are microporous silica-aluminates with micropores of dimensions comparable to organic molecules. The materials are unique, because these micropores are determined by the three-dimensional crystallographic structure of the material and catalytic events occur at the interphase of zeolite micropore and zeolite lattice. As a result the catalytically active sites are well defined. Zeolites are used in practice in the acidic form or promoted with metal or sulfide particles. High Resolution Electron Microscopy, Neutron Diffraction and Solid State NMR are techniques that arc applied for structural characterization and to study the behaviour of chemisorbed molecules. 

The preceding discussion of inorganic microporous structures illustrates the great variety of metal eations that may be accommodated in porous frameworks. By contrast, relatively little progress has been made in the preparation of porous frameworks with anions other than oxide ions. The obvious candidates are nitrides and sulfides and there have been some reeent advances in these directions. 

It is possible to oxidise and reduce atoms in the framework and also those within the pores of microporous (and mesoporous) solids of appropriate chemical compositions. Although pure aluminosilicate, silicate and aluminophosphate frameworks cannot be oxidised or reduced, transition metal and some lanthanide cations within the framework can exist in different oxidation states. Also, although typical alkali, alkali metal and most lanthanide cations in extraframework positions possess no redox chemistry, transition metal cations such as nickel, copper and platinum do. In the case of the transition metals, this enables them to become important catalysts. The included sulfide species in ultramarine-related pigments described above are also prepared through the reduction of sulfate species. 

Sulfide Molecular Sieves. All crystalline molecular sieves and microporous crystals have so far been based on oxide frameworks. As discussed previously, the oxide-based molecular sieve family shows rich compositional and structural diversity, and the number of new species is still growing at a rapid rate. An important new direction for molecular sieves is provided by the recent discovery of sulfide-based molecular sieves. The first publication on these materials already described a whole family of sulfide molecular sieves containing germanium (Ge) and tin (Sn) or several other metals. The crystal structures are all new and include 12 unique framework structures. These materials may have potential applications using sulfur-containing feedstocks in which the sulfur present may stabilize the composition of the sulfide molecular sieve. 

The deposits from hot deep-well brine near the Salton Sea in California build up very rapidly as the brine cools while going through pipes. The silica content is 400 ppm in a solution containing up to 15% Nad as well as a few percent of CaCl, and KCI. The brine is slightly acidic, so there is no interaction of silica with calcium ion, but iron, which is present at only 0.2%, is adsorbed on silica at this pH and is a major component of the scale. More striking is that up to 20% copper and 6% silver are found in the scale as sulfides. The deposit is amorphous to X-rays and consists of a hydrated silica, classed as opal, but is actually a microporous silica gel, under the coagulating influence of the metal ions. Since the brine contains 1-2 ppm H,S, the... 

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