Silver silica-alumina

More widely used promoters for this purpose are silver zeolite and silver silicate, which were developed by Paulsen [18] and Garegg [19], respectively. Although not being commercially available, these reagents can be conveniently prepared from silver nitrate and proved to be quite powerful. More recently, van Boeckel developed the use of silver silica-alumina, which was reported to be more reactive than other insoluble salts and to have an enhanced cation capacity [20]. Representative examples of successful y0-mannosylation by using insoluble salts are depicted inO Scheme 8 [19,21,22]. 

Thermal compounds are typically highly filled with silver, silica, alumina oxide, or diamond powder and usually have a high viscosity. 

Silver(I)-loaded zeolites and silica-alumina can be used in carbohydrate coupling. The Ag(I) activates the 1-Br-substituent in this nucleophilic substitution. Because of the size of the reactants only the outer surface of the zeolites is active. 

Soil, sediment (2,3,7,8-TCDD) Soxhlet extraction of sample volume reduction clean-up on basic silica/acidic, silica/alumina, elution with CH2CI2 in hexane analysis clean-up on silver nitrate silica or 2,3,7,8-TCDD-specific alumina, elution with CH2CI2 in hexane analysis repeating of clean-up or extraction if needed HRGC/LRMS (SIM) HRGC/MS/MS (SIM) 1 ng/g <1 ng/g 40-90 57-102 Simon et al. 1989... 

Sodium borate Titanates Inorganic ceramic Boric oxide Silica Alumina Calcium fluoride Metal Silver Nickel Gold Tantalum Indium/lead ... 

The major products were -( ) and y- (II) picolines traces of pyridine and small amounts of ethylpyridines and higher molecular weight bases were also formed. Similar products have been observed when the same reactants were passed over silica-alumina 148). Zeolite catalysts, notably silver-exchanged X-type faujasites, have also proven effective in the synthesis of methylpyridines from acetylene and NHs, and methylacetylene and NHs, at temperatures ranging from 100° to 300° 149). 

Preferred catalysts generally are silica/alumina compositions which may be impregnated with promoters, such as silver phosphate, cobalt sulfide, etc. 

All present industrial catalyst systems are based on silver deposited on a slightly porous solid. The most widely used support is x-alumina, but silica-alumina and carborundum can also be employed. The specific surface area of the support, its porosity, and the pore size exert a considerable influence on the metal distribution at the surface, and consequently on catalytic activity. Several techniques are also available for fixing the silver, either by impregnation from a solution, or by deposition from a suspension. An initiator, usually consisting of alkaline earth or alkaline metals, can be added to the catalyst, but other metallic additions have also been recommended. Certain halogenated organic derivatives, such as dichloropropane, may increase selectivity in trace amounts (10 ppm in the feed), by reducing combustion side reactions. 

Silver oxide precipitated on silica gel by either ammonia or sodium hydroxide is very active (15) even in the presence of oil and water vapor but a coprecipitated silver oxide-alumina contact containing about 10% silver was entirely inert under similar conditions (18). 

Of particular interest to adhesives formulators are nanofillers such as carbon nanotubes (CNT), silica, alumina, magnesium oxide, titanium dioxide, zirconium oxide (Zn02), silver, copper, and nickel). Of these, carbon nanotubes are the most widely studied for electrically conductive adhesives to attach microdevices, to interconnect microcircuits and to increase I/O densities at the device level. ... 

Materials possessing charged surfaces include almost all of the inorganic oxides and salts of technological importance (silica, alumina, titania, etc.), the silver halides, latex polymers containing ionic comonomers, and many natural surfaces such as proteins and cellulosics. It is very important, therefore, to understand the interactions of such surfaces with surfactants or other adsorbates in order to optimize their effects in such applications as paint and pigment dispersions, papermaking, textiles, pharmaceuticals, and biomedical implants. 

Cryolite melts (NasAlFe, mp 1273 K), which are of considerable importance in aluminum refining studies, need to be purified from refractory oxides (silica, alumina, etc.) and iron, among others. Preelectrolysis at 1.6 V using a molten silver cathode in a graphite or molybdenum crucible is recom-mended. " "" ... 

MOR depends on whether the silver is reduced. Table 14.9 summarizes the solid adsorbents available for iodine capture. The silver-based alumina, silica, and mordenite adsorbents have comparable characteristics and are the currently preferred sorbents. An advantage of the mordenite is that the regeneration of the sorbent is possible, thereby utilizing the silver over the course of several cycles. The stripped iodine is then available for sorption using a cheaper metal or conversion to a waste form preferred for long-term storage. 

Noh J., Yang O.B., Kim D.H., Woo S.I. Characteristics ofthe Pd-only three-way catalysts prepared by sol-gel method. Catal. Today 1999 53 575-582 Noto S.Y., Sachtler W.M.H. Infrared spectra of carbon monoxide adsorbed on supported palladium and palladium-silver alloys. J. Catal. 1974 32 315-324 Ochoa R., van Woet H., Lee W.H., Subramanian R., Kugla- E., Eklund PC. Catalytic degradation of medium density polyethylene over silica-alumina supports. Appl. Catal. A Gen. 1996 49 119-136... 

Most equi-axed nanoparticles are spherical, but irregular particles are also available. The common particles are metallic (e.g., gold, silver), ceramic (e.g., silica, alumina, titania), or organic (e.g., rubber particles, fullerenes). The ceramic particles are typically prepared by sol-gel or flame-spraying methods silica and alumina are commonly used with adhesives, see O Pig. 55.1. Rubber particles are typically core-shell particles, with a soft core and a hard shell of a polymer such as poly(methyl methacrylate). 

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

Cobalt ores are often found in association with copper(II) sulfide. Cobalt is a silver-gray metal and is used mainly for alloying with iron. Alnico steel, an alloy of iron, nickel, cobalt, and aluminum, is used to make permanent magnets such as those in loudspeakers. Cobalt steels are hard enough to be used as surgical steels, drill bits, and lathe tools. The color of cobalt glass is due to a blue pigment that forms when cobalt(II) oxide is heated with silica and alumina. 

McIntyre et al. [58, 59] described a method for the analysis of polychlorobiphenyls and chlorinated insecticides in sewage sludges in which homogenized samples are extracted with hexane, concentrated and cleaned up on an alumina/alumina plus silver nitrate column and eluted with hexane. After concentration of the eluent, polychlorobiphenyl and organochlorine compounds were determined by a silica gel chromatographic procedure and gas chromatography. 

Catalytic forms of copper, mercury and silver acetylides, supported on alumina, carbon or silica and used for polymerisation of alkanes, are relatively stable [3], In contact with acetylene, silver and mercury salts will also give explosive acetylides, the mercury derivatives being complex [4], Many of the metal acetylides react violently with oxidants. Impact sensitivities of the dry copper derivatives of acetylene, buten-3-yne and l,3-hexadien-5-yne were determined as 2.4, 2.4 and 4.0 kg m, respectively. The copper derivative of a polyacetylene mixture generated by low-temperature polymerisation of acetylene detonated under 1.2 kg m impact. Sensitivities were much lower for the moist compounds [5], Explosive copper and silver derivatives give non-explosive complexes with trimethyl-, tributyl- or triphenyl-phosphine [6], Formation of silver acetylide on silver-containing solders needs higher acetylene and ammonia concentrations than for formation of copper acetylide. Acetylides are always formed on brass and copper or on silver-containing solders in an atmosphere of acetylene derived from calcium carbide (and which contains traces of phosphine). Silver acetylide is a more efficient explosion initiator than copper acetylide [7],... 

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