Amorphous aluminas

Small amounts of sodium aluminate are prepared in the lab by fusion of equimolar quantities of sodium carbonate [497-19-8] and aluminum acetate [139-12-8], A1(C2H202)3, at 800°C (4). Other methods involve reaction of sodium hycboxide with amorphous alumina or aluminum [7429-90-5] metal. Commercial quantities of sodium aluminate are made from hydrated alumina, in the form of aluminum hydroxy oxide [24623-77-6], AIO(OH), or aluminum hycboxide [21645-51 -2], Al(OH)3, a product of the Bayer process (5,6) which is used to refine bauxite [1318-16-7], the principal aluminum ore. 

The CF and GF represent the coke- and gas-forming tendencies of an E-cat compared to a standard steam-aged catalyst sample at the same conversion. The CF and GF are influenced by the type of fresh catalyst and the level of metals deposited on the E-cat. Both the coke and gas factors can be indicative of the dehydrogenation activity of the metals on the catalyst. The addition of amorphous alumina to the catalyst will tend to increase the nonselective cracking, which forms coke and gas. 

The extent to which small particles of Pd and Pt show evidence of oxidation after exposure to air Is also highly variable. It Is difficult to confirm the evidence of X-ray diffraction and EXAFS (25) that most particles In the 15-20A size range consist entirely of oxide. We have found that such particles usually give single crystal patterns attributable to the metals. There Is, however, considerable evidence that, in the case of Pt on alumina, the Pt crystals have a well-defined epitaxial relationship with the crystallites (20-50A diameter) of the nominally "amorphous" alumina substrate. 

Figure 32. Structure of amorphous alumina showing a single A1406 group (a), a sheet of these (b), and a stack of sheets (c).189...

Besides the amorphous alumina films formed in the majority of acidic electrolytes (except those formed in chromic acid and exhibiting traces of y-Al203194), there are possibilities of forming oxides with a more or less pronounced crystallinity. These oxides are formed in alkaline solutions195 and especially in sodium carbonate baths.196 According to the data provided by Hiroshi and Yoshimura,197 these oxides contain a y- A1203 phase easily hydrated and converted into a bayerite-like substance. 

The main components of FCC catalysts are Zeolite Y, e.g., REY orUSY as the major active component (10 to 50%), and a binder that is typically an amorphous alumina, silica-alumina, or clay material. In addition to these main components, other zeolite components, e.g., ZSM-5, and other oxide or salt components are quite frequently used additives in the various FCC catalysts available on the market. The addition of 1 to 5% ZSM-5 increases the octane number of the gasoline. ZSM-5 eliminates feed compounds with low octane numbers because it preferentially center-cracks n-paraffins producing butene and propene [14], These short-chain olefins are then used as alkylation feedstocks... 

Non-porous amorphous alumina films (several hundred Angstroms thick) can be prepared by the anodic oxidation of clean, high-purity Al. The oxide film is separated by dissolving any unoxidized metal in a mercury chloride solution. The oxide films are then washed in distilled water and collected on suitable electron microscopy grids. They are dried and heated to 800 "C to obtain amorphous AI2O3. High-purity wires of the desired metals can then be vacuum evaporated on to the films in an evaporator. These films can also be prepared using Al-nitrate,... 

Figures 15.12 and 15.13 illustrate the results obtained using the above method on a porous amorphous alumina sample. A distinct advantage of the flow system for these measurements is that data points can be obtained where they are desired and not where they happen to occur after dosing, as...

An opposing effect is possible under the severe conditions of a single extraction with HC1 some of the aluminum removed from the crystal structure may not be transported out of the catalyst particle. The resulting amorphous alumina, (after subsequent calcining) remaining in the particle would cause some reduction in effective diffusivity. Such amorphous alumina has been suggested by others (17,18). 

High Alumina Clay Minerals. Several hydrated alumina minerals should be grouped with the clay minerals because the two types may occur so intimately associated as to be almost inseparable. Diaspore (a-AIO(OH)) and bochmitc (y-AIO(OH)). both AFOj H 0(AI Oi. 85% H 0. 15%) are Ihe chief constituents of diaspore clay, which may contain over 75% AhOj on the raw basis. Gibbsite, AliOj 3 HyO (AljOi. 65.4% HjO. 34.6%). and cliachite. the so-called amorphous alumina hydrate (much cliachite is probably cryptocryslalline), as well as Ihe monohydrates, occur in hauxile, bauxitic kaolin, and bauxitic clays. 

Corundum is aluminum oxide, q -A1203, which has a hexagonal crystalline structure that is analogous to hematite. However, water treatment systems most often use activated alumina, which is typically produced by thermally dehydrating aluminum (oxy)(hydr)oxides to form amorphous, cubic (y), and/or other polymorphs of corundum (Clifford and Ghurye, 2002, 220 Hlavay and Poly k, 2005 Mohan and Pittman, 2007). When compared with corundum, amorphous alumina tends to have higher surface areas, greater numbers of sorption sites, and better sorption properties. 

Ross and Kerr (1934), Jaffe and Sherwood (1950), White (1953), and others have described phosphate-bearing allophane. P2O5 values in the 7-10% range appear to be relatively common. The similarity of the silica tetrahedra and the phosphorous tetra-hedra would favor such an association. Evansite is an amorphous alumina phosphate and Ross and Kerr (1934) suggested it may occur mixed with allophane. However, it is also possible that the phosphate tetrahedron is a substitute for the silica tetrahedra and occurs as an intimate part of the allophane complex. 

In order to properly compare the catalytic activity of these two types of materials, a sample of SAPO-37 free of amorphous alumina (S37-4) with 35 Si/u.c., has been prepared. Its catalytic activity is compared in Figure 7 with that of a USY zeolite with unit cell of 2.442 nm described in previous studies (29). The sample... 

Although a lot of research has been reported on the use of various carbonaceous materials in defluoridation, no known column or full-scale plant operation is easily available in open literature. One reason for this is that most carbonaceous materials show poor adsorption capacity (Table 4) for fluoride and therefore only laboratory-scale performances have so far been reported. Amorphous alumina supported on carbon nanotubes on the other hand show high capacity (28.7 mgF/g adsorbent) for fluoride and is therefore a promising material for drinking water defluoridation. 

Masson, A., Bellamy, B., Romdhane, Y. H., Che, M., Roulet, H., and Dufour, G., Intrinsic size effect of platinum particles supported on plasma-grown amorphous alumina in the hydrogenation of ethylene. Surf. Sci. 173, 479 (1986). 

Our support precursor having a Mg Al molar ratio of about 3 1 shows an x-ray diffraction pattern typical of hydrotalcite (see Figure la) (10). After calcination at 873 K the resulting diffraction pattern exhibits diffuse peaks corresponding to MgO (Figure lb). No evidence for separate crystalline aluminum phases was found so A1 cations probably remain closely associated with or dissolved in the MgO structure. However, it is possible that amorphous alumina phases, not detectable by x-ray diffraction, may be present in our mixed oxide. 

The catalysts used for cracking before the 1960s were amorphous [Si-Al] catalysts. The replacement of these catalysts by faujasite zeolites was a big step forward in the oil refining industry, which led to an increase in the production of gasoline [20], The acid catalyst, currently used in FCC units, is generally composed of 5-40 wt % of 1-5 pm crystals of the H-Y zeolite included in a porous particle composed of an active matrix, which in turn is composed of amorphous alumina, silica, or [Si-Al] and a binder. The porous particle allows the diffusion of the reactants and products of the cracking reaction to and from the micropores of the zeolite [10]. 

Ghorbel and co-workers (329) have shown that the dependence of the rate of 1-butene isomerization at 260°C on the activation temperature of an amorphous alumina shows two maxima near 470° and 650°C. This behavior nicely parallels the surface concentration of the cation radicals formed on PhTh adsorption (see Fig. 5) as well as that of the anion radicals formed on TCNE adsorption (see... 

Recent studies by Maret et al. have investigated the process of spillover activation of amorphous alumina (135,136). If the sample was cooled in H2 from 430 to 180°C with the source of spillover present (supported Pt), no induction period was found for ethylene hydrogenation. This implies that... 

Another interesting reaction on amorphous alumina activated by Pt/Al203 activator (at 430°C) was the isomerization of many doses of... 

Fig. 20. Isobaric representation of spiltover hydrogen adsorption on activated aluminas, amorphous or d (and silica) (A) <5-alumina (and silica), with Pt/Al203 (B) amorphous alumina with Pt/Al203 (C) i5-alumina without Pt/Al203 (D) amorphous alumina without Pt/Al203.

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