Alumina-based compound

Several aluminum- and titanium-based compounds have been supported on silica and alumina [53]. Although silica and alumina themselves catalyze cycloaddition reactions, their catalytic activity is greatly increased when they complex a Lewis acid. Some of these catalysts are among the most active described to date for heterogeneous catalysis of the Diels-Alder reactions of carbonyl-containing dienophiles. The Si02-Et2AlCl catalyst is the most efficient and can be... 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

The lipophilicity and specific surface area of a similar set of synthetic dyes was also determined on an alumina-based RP-TLC stationary phase and the linear relationship between the two hydrophobicity parameters was calculated. The result of the calculation is depicted in Fig. 3.6. The good correlation between these physicochemical parameters indicated that from the chromatographic point of view these compounds behave as a homologous series of analytes, however, their chemical structures are markedly different [87],... 

The derivation of a mechanism for a chemical reaction is by its very nature an uncertain process, being dependent critically on the nature and extent of the experimental evidence. Mechanisms that have at their heart a surface process or processes are even more uncertain and when the constraints imposed by the manipulation of HF are also taken into account, it is not surprising that there have been relatively few mechanistic studies made of heterogeneous catalytic fluorination. However a catalytic process cannot be said to be understood fully without a mechanism based on the experimental evidence available and such studies are helpful in the design of the next generation of catalysts. In most cases the work described below involves chromia or y-alumina based catalysts that have been pretreated according to the methods described above. Studies involving C2 and Q compounds are described in turn. 

II. Properties of Phosphorus-Based Compounds Related to the Co(Ni)-Mo-P-Alumina System... 

Tn 1972 Alberta produced 8 X 106 long-tons of elemental sulfur by sweetening sour gas (I), i.e., a natural gas containing an appreciable amount of hydrogen sulfide. Hydrogen sulfide and other sulfur compounds are converted to sulfur by the well known modified Claus process using alumina-based catalysts. The basic chemical reactions are ... 

Supported ionic liquid compositions are also a vivid field of research in which many companies tried to make their claims [88-90]. By immobilizing ionic liquids onto silica- or alumina-based carriers it is possible to obtain new Lewis acid catalysts with interesting characteristics. These are presently preferably used for alkylation and acylation reactions of aromatic compounds [91, 92] or isomerizations. Even the co-immobilization of ionic liquids with transition metal complexes [93] or Lewis acids [94] has been described, and it can be anticipated that this particular field offers many options for future catalyst development. 

The selective oxidation of an alloy component, e.g., A1 or Si, requires the alumina or silica to be more stable than the oxides of the other components in the alloy. Figure 2.5 indicates this condition would be met for compounds such as nickel aluminides and molybdenum silicides. However, in the case of Nb- or Ti-base compounds the oxides of the base metal are nearly as stable as those of A1 or Si. This can result in conditions for which selective oxidation is impossible. This situation exists for titanium aluminides containing less than 50 at% A1 as illustrated in Figure 5.27. In this case a two-phase scale of intermixed AI2O3 and I1O2 is generally observed. It should be emphasized that the determination of which oxide is more stable must take into account the prevailing metal activities. 

The processes used to prepare alumina based fibers by the solution route start with precursors which are either an aqueous solution of an aluminum salt or a solution of an organoaluminum compound in an organic solvent. The level of viscosity required for spinning is achieved by properly controlling the degree of hydrolysis/polycondensation of the precursor... 

Beryllium oxide-based ceramics are in manyways superiorto alumina-based ceramics. The major drawback is the toxicity of BeO. Beryllium and its compounds are a group of materials that are potentially hazardous and must be handled properly. With the necessary safeguards, BeO has been used successfully in many tube designs. 

The IRVAD process by Black Veatch Pritchard Inc. and Alcoa Industrial Chemicals is claimed to be a low-cost process for low-sulflir gasoline . The process uses an alumina-based selective adsorbent to counter-currently contact liquid hydrocarbon in a multistage adsorber. The adsorbent is regenerated in a continuous cross-flow reactivator using heated reactivation gas. The process operates at lower pressure, and does not consume hydrogen or saturate olefins. The adsorption mechanism is based on the polarity of sulfur compounds. It is not very selective for gasoline sulfur, and no information is available on diesel sulfur. 

Fireclay bricks (alumina silica bricks, alumina calcium oxide silica bricks, and other silicate bricks) are not optimal barrier materials for A1 reductirMi cells. As we have mentioned, cryolite-based electrolyte for A1 reduction is a substance that dissolves alumina better than anything else. Certainly, it will dissolve all alumina-based refractory compositions and almost all other oxides similar in chemical structure to alumina. From a chemical point of view, the effective refractory barriers against the penetration of cryolite might be tin oxide, nickel oxide, compounds of nickel oxide, iron oxide, or zinc oxide (such as spinel Fe NiOs). These oxides almost do not react with NaF and aluminium fluoride [175]. Yet the cost of these materials, which is 50-100 times higher than that of firebrick, provides the impetus to find less costly variants of alumina silica materials. 

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