Supports Kieselguhr

Divanadium(V) oxide catalysts are currently almost exclusively used. They are fused salts, which in a cold state consist essentially of vanadium sulfate and potassium disulfate, applied to a porous support (kieselguhr or diatomaceous earth). The change in valency state between and V -ions is probably a critical. step in the catalysis. The lowest operating temperature of this catalyst is generally ca. 420 to 440°C. 

The physical structure, which can be changed by suitable methods of catalyst manufacturing, is. of decisive importance (promoters high-melting oxides supports kieselguhr of cobalt and nickel catalysts pretreatment low-temperature reduction which limits the size of the crystals, or carbon monoxide treatment of iron catalysts which increases the surface by breaking up the structure with carbon). 

The classic catalyst consists of Co-Th02-MgO mixtures supported on Kieselguhr (see Ref. 269) group VIII metals, especially Ni, generally are active,... 

Benzene-Based Catalyst Technology. The catalyst used for the conversion of ben2ene to maleic anhydride consists of supported vanadium oxide [11099-11-9]. The support is an inert oxide such as kieselguhr, alumina [1344-28-17, or sUica, and is of low surface area (142). Supports with higher surface area adversely affect conversion of benzene to maleic anhydride. The conversion of benzene to maleic anhydride is a less complex oxidation than the conversion of butane, so higher catalyst selectivities are obtained. The vanadium oxide on the surface of the support is often modified with molybdenum oxides. There is approximately 70% vanadium oxide and 30% molybdenum oxide [11098-99-0] in the active phase for these fixed-bed catalysts (143). The molybdenum oxide is thought to form either a soUd solution or compound oxide with the vanadium oxide and result in a more active catalyst (142). 

Phosphates are the principal catalysts used in polymerization units the commercially used catalysts are Hquid phosphoric acid, phosphoric acid on kieselguhr, copper pyrophosphate pellets, and phosphoric acid film on quartz. The last is the least active and has the disadvantage that carbonaceous deposits must occasionally be burned off the support. Compared to other processes, the one using Hquid phosphoric acid catalyst is far more responsive to attempts to raise production by increasing temperature. 

Currently, almost all cumene is produced commercially by two processes ( /) a fixed-bed, kieselguhr-supported phosphoric acid catalyst system developed by UOP and (2) a homogeneous AlCl and hydrogen chloride catalyst system developed by Monsanto. 

Supports. The principal component of a typical catalyst is the porous support (49,50). Most supports are robust soHds that can be made with wide ranges of surface areas and pore size distributions. The most widely appHed supports are metal oxides others are carbon, kieselguhr, organic polymers, and zeoHtes. 

Composition. Among the most commonly used support materials are aluminas, siUcas, and aluminosihcates with a wide range of alumina to sihca ratios, as well as activated carbon, siUcon carbide, selected clays, various ceramics, artificial and natural 2eohtes, kieselguhr, and pumice. Polymeric... 

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Supported palladium, zirconium-promoted cobalt on kieselguhr, or nickel on kieselguhr can be used under relatively mild conditions to effect reduction of the nitrile function without hydrogenating the ring. 

Nickel. As a methanation catalyst, nickel is presently preeminent. It is relatively cheap, it is very active, and it is the most selective to methane of all the metals. Its main drawback is that it is easily poisoned by sulfur, a fault common to all the known active methanation catalysts. The nickel content of commercial nickel catalysts is 25-77 wt %. Nickel is dispersed on a high-surface-area, refractory support such as alumina or kieselguhr. Some supports inhibit the formation of carbon by Reaction 4. Chromia-supported nickel has been studied by Czechoslovakian and Russian investigators. 

For example, while reaction of 2-butoxynaphtalene with copper(II) bromide in benzene at 50°C for 2 h. produced only 6 % yield of l-bromo-2-butoxynaphtalene, similar reaction with Kieselguhr-supported copper(II) bromide gave 86 % yield of the monobromide. On the other hand, reaction using alumina as a support in benzene proceeded completely even at 10°C in 1 h. to give in addition to the monobromide (77 %), the dibromide (21 %) and the binaphtyl (2 %). 

A mixture of 1-methoxynaphtalene (1.90 g, 12 mmol) and Kieselguhr-supported copper(II) bromide (24 g) in benzene (150 ml) was stirred at 30°C for 3 h. The rnixmre was filtered, and the spent reagent was washed with benzene. The combined filtrate was concentrated, and the residue was distilled under vacuum to give 2.3 g (85 %) of 4-bromo-1-methoxynaphtalene. Bp 155-157°C/5 Torr (lit. 159-160°C/5 Torr (ref 15)). 

Fig. 2. (a) Magnetization-volume isotherms for the chemisorption of hydrogen and of benzene on kieselguhr-supported nickel at 150° C (16). (b) Average number of bonds formed by benzene adsorbed on nickel-silica as a function of temperature (17). From J. Amer. Chem. Soc. 79, 4637 (1957) 83, 1033 (1961). Copyright by the American Chemical Society. Reprinted by permission of copyright owner. 

In this connection, it must also be borne in mind that the deoxyribonucleic acids subjected to analysis have probably not been homogeneous. Deoxyribonucleic acids have been fractionated by making use of their different solubilities in normal saline,186 by extracting thymus nucleo-his-tone with sodium chloride solutions of increasing concentration,187 by ion-exchange,187 and also by adsorption of the polynucleotide onto histone immobilized on a kieselguhr support.123 It is possible, however, that these are artefacts, since it has been shown that deoxyribonucleic acid fractions extracted from calf-thymus nucleohistone may or may not vary in composition according to the previous treatment of the material.188... 

Since cobalt on kieselguhr in one of the original Fischer-Tropsch catalysts (1-9), it appeared attractive to investigate the catalytic activity of cobalt complexes immobilized on polystyrene. Although there are many supported cobalt-based Fischer-Tropsch catalysts known (see, for example, references 18-21), no polystyrene-bound systems had been reported. During the course of our work 18% (22,60,61) and 20% (23) crosslinked analogs of CpCo(C0)2 were shown to exhibit limited catalytic activity but no CO reduction. A preliminary disclosure of our work has appeared (2)4). 

In a partition system the stationary phase is a liquid coated onto a solid support (p. 97). Silica gel, kieselguhr (diatomaceous earth) or cellulose powder are the most frequently used. Conditions closely resemble those of counter-current distribution so that in the absence of adsorption by the solid support, solutes move through the system at rates determined by their... 

Further examples are furnished by the spectra of Figs. 10 and 11. A single pellet of virgin catalyst ( 7 x 10mm) was placed in a cell (Fig. 2) and degassed at room temperature, and spectrum S2 was recorded (the main spectral features are the strong absorptions of the kieselguhr support, but some sulfate absorptions can also be discerned). The catalyst was then exposed to 90 torr of SO2 at room temperature and spectrum was recorded with SO2 in the cell, when new features appeared. 

The silica carrier of a sulphuric acid catalyst, which has a relatively low surface area, serves as an inert support for the melt. It must be chemically resistant to the very corrosive pyrosulphate melt and the pore structure of the carrier should be designed for optimum melt distribution and minimum pore diffusion restriction. Diatomaceous earth or synthetic silica may be used as the silica raw material for carrier production. The diatomaceous earth, which is also referred to as diatomite or kieselguhr, is a siliceous, sedimentary rock consisting principally of the fossilised skeletal remains of the diatom, which is a unicellular aquatic plant related to the algae. The supports made from diatomaceous earth, which may be pretreated by calcination or flux-calcination, exhibit bimodal pore size distributions due to the microstructure of the skeletons, cf. Fig. 5. 

Butanol, reaction over reduced nickel oxide catalysts, 35 357-359 effect of ammonia, 35 343 effect of hydrogen, 35 345 effect of pyridine, 35 344 effect of sodium, 35 342, 351 effect of temperature, 35 339 over nickel-Kieselguhr, 35 348 over supported nickel catalysts, 35 350 Butanone, hydrogenation of, 25 103 Butene, 33 22, 104-128, 131, 135 adsorption on zinc oxide, 22 42-45 by butyl alcohol dehydration, 41 348 chemisorption, 27 285 dehydrogenation, 27 191 isomerization, 27 124, 31 122-123, 32 305-308, 311-313, 41 187, 188 isomerization of, 22 45, 46 isomers... 

The reactor is a vessel with beds of solid catalyst. Most commercial processes use a catalyst called kieselguhr, which is phosphoric acid deposited on a silica/alumina pellet. Because of the weight of the pellets, supported beds at multiple levels in the vessel are used so the bottom layers wont be crushed.-... 

Novasyn KA constits of kieselguhr supported dimethylacrylamide functionalized with sarcosine methylester. 

Nickel catalysts are universal and are widely used not only in the laboratory but also in the industry. The supported form - nickel on kieselguhr or infusorial earth - is prepared by precipitation of nickel carbonate from a solution of nickel nitrate by sodiiun carbonate in the presence of infusorial earth and by reduction of the precipitate with hydrogen at 450° after drying at 110-120°. Such catalysts work at temperature of 100-200° and pressures of hydrogen of 100-250 atm 43. ... 

Hexane-1,6-diol was found to undergo an oxidation-cyclization process at elevated temperatures (250 °C) in the presence of a Cu-Cr catalyst supported on kieselguhr to yield 2,3,4,5-tetrahydrooxepin (68) (65JOC335). The final stage of the latter reaction involves a dehydration of the hemiacetal 2-hydroxyoxepane (75) as indicated in equation (38). An alternative type of base-induced cyclization (equation 39) involving intramolecular nucleophilic attack has been used in the synthesis of 4-ethoxycarbonyI-2,3,6,7-tetra-hydrooxepin (153) (73JOC1767). 

Packed columns contain an inert and stable porous support on which the stationary phase can be impregnated or bound (varying between 3 to 25%). The solid support is made of spheres of approximately 0.2 mm in diameter, obtained from diatomites, silicate fossils (such as kieselguhr, tripoli) whose skeleton is chemically comparable to amorphous silica. These materials, which have a specific surface area ranging from 2 to 8 m2/g, have been commercialised by several companies such as Johns Manville, under the name of Chromosorb , and are used universally. Other synthetic materials have been developed such as Spherosil , made of small silica beads. All of these supports have a chemical reactivity comparable to silica gel because of the presence of silanol groups. 

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