Alumina Materials

Pietrzyk and coworkers [21] showed that hydrated alumina can function as a low-capacity anion exchanger. The isoelectric pH for alumina is about 7.5 and its ion-exchange capacity (about 2 mequiv/g maximum) is dependent on the sample ion, the eluent pH, and the pretreatment of the alumina. The alumina must be first hydrated and then treated with either an acid or base. Anion-exchange capacity increases as the eluent pH is made more acidic. The changeover from an anion exchanger to a cation exchanger is gradual and occurs in the vicinity of eluent pH 7.5. 

In anion chromatography the elution order of common anions is almost the reverse of conventional resins. Fluoride and phosphate are so strongly held by the alumina that elution is often impossible. 

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The first commercial fluidized cracking catalyst was acid-treated natural clay. Later, synthetic. silica-alumina materials containing 10 lo... 

The Ag-silica-alumina material is furthermore suited to assist in sterically hindered aromatic brominations. As an example we converted 1,3,5-tri-t-butylbenzene into 2,4,6-tri-t-butylbromobenzene. When using an acidic zeolite and Br2 de-alkylation prevails and 3,5-di-t-butylbromobenzene is formed (ref. 29). 

There is no clear evidence to identify the active material for SO2 removal in a MgAl20 stoichiometric system. Figure 13 shows results for a 50-50 mole% magnesia-alumina material prepared from magnesium hydroxide and alumina sol and calcined at various temperatures. An attempt was made to correlate SO2 removal with compound formation, as measured by X-ray diffraction, and surface area. As indicated in the figure, SO2 removal ability decreased with Increasing calcination temperature as did surface area. X-ray diffraction analysis showed spinel formation increases as... 

The preparation of precious metal supported catalysts by the HTAD process is illustrated by the synthesis of a wide range of silver on alumina materials, and Pt-, Pt-Ir, Ir-alumina catalysts. It is interesting to note that the aerosol synthesis of alumina without any metal loading results in a material showing only broad reflections by XRD. When the alumina sample was calcined to 900°C, only reflections for a-alumina were evident. The low temperature required for calcination to the alpha-phase along with TEM results suggest that this material was formed as nano-phase, a-alumina. Furthermore, the use of this material for hexane conversions at 450°C indicated that it has an exceptionally low surface acidity as evidenced by the lack of any detectable cracking or isomerization. 

However, the extent of the activity enhancement cannot be related to the higher surface area of this material. Two possible explanations were proposed to account for the effect of mirror plane composition on combustion activity one is related to the different oxidation state of the cation in the mirror plane the other is associated with the crystal structure of layered-alumina materials (i.e., magne-toplumbite and (3-Al203) which have different population and co-ordination of the ions in the mirror planes. Both these electronic and structural factors can, in principle, affect the redox properties. 

Oxidative polymerization of 1,4-diethynylbenzene into highly conjugated poly(phenylene butadiynylene) within the channels of surface-functionalized mesoporous silica and alumina materials. J. Am. Chem. Soc. 124 9040-9041. 

Among the various electrolytes, yttrium stabilized zirconia (YSZ) has been developed, for use in high-temperature fuel cells and oxygen sensors similarly, various S( S")-alumina materials are in development for sodium sulfur batteries. 

In a gasifier utilizing gas or liquid as a carbon source, refractory failure is primarily caused by thermal, chemical, and structural wear of the refractory liner. The hot face refractory lining in the gasifier is typically a dense high-alumina material (low in Si02 and FeO), followed by a porous layer composed of a material such as... 

Bronsted acid sites can be directly probed through solid-state H NMR spectroscopy, as chemical shifts can be correlated with acid strength [195, 197, 198]. The precise chemical shift observed for any given Bronsted acid site is dependent on the material upon which it is located. For instance, on silica values of 1.6ppm are typically observed zirconia has two distinct OH sites, at 2.4 and 4.8ppm while on alumina a typical range may be -0.2 to 4.3 ppm. Early studies employing H NMR to study Bronsted acid sites focused on the characterization of the surface of amorphous silica-alumina materials [165, 199-201]. Extensive work, however. 

It is generally accepted that thermal and especially hydrothermal treatment of aluminas and other catalytic materials results in deterioration of porous structure, i.e. increase in average pore radius and diminishing in specific surface area [1-4]. It is very important that such alumina materials as some catalyst washcoats and membranes have to be exploited at higher temperatures and at atmosphere of large humidity. Therefore it is necessary to improve their thermal and hydrothermal stabilization by application of new binder materials or additives. Such additives as silica, ceria or zirconia are known as thermal stabilizers. The aim of this work was to determine the influence of addition of the selected stabilizers on hydrothermal stability of alumina material in the temperature range 150 - 225 °C and time up to 72 hours. 

DN-550TS = a sample prepared from Disperal type aluminum hydroxide kneaded with 1% water solution of nitric acid, calcined 4 h at 550 C, coated with TEOS and coated with silica sol. We have selected concentrations of TEOS, silica sol and cerium nitrate at the level allowing obtaining ca 1.8 wt % of the individual stabilizers in final alumina material. 

The further results given in Table 1 also indicate that some influence on supports structure transformation under hydrothermal conditions exerts type of used peptising agent. It was found that supports formed with using of nitric acid solution are more hydrothermally stable than alumina material formed with using of Culminal (DN-800 and DC-800 supports). The average pore radius in the case of DC-800 sample after hydrothermal treatment was two times larger than for DN-800 sample after the same treatment. 

Amorphous silica-alumina materials represent an important class of porous inorganic solids which have not long-range order and usually have a wide distribution of the pore size, in the micro and mesopore region. They show outstanding catalytic behaviours in several acid catalysed reactions (5, 6). 

In order to evaluate correctly the textural properties a carefully selection of calculation method is necessary. Evaluation of micropore volume in ERS-8 and SA calculated with Dubinin-Radushkevich and DFT are consistent, instead an overestimate value is observed with Horvath-Kavazoe method. The pore size distribution of MSA, MCM-41, HMS and commercial silica-alumina materials have been evaluated by BJH and DFT method. Only DFT model is effective, in particular for evaluation in the border line range between micro and mesopores. 

Alumina materials are manufactured on the basis of / -Al203 with a minimum addition of alkali flux, so that no glass is present in the product (this results in good thermal shock resistance) but more often on the basis of a-Al203 (corundum) or its solid solution with Cr203. 

The first two methods are preferred in industrial applications. They are used for producing porous insulating materials of fireclay, silica, high-alumina materials, magnesite, stabilized zirconia etc. Their thermal conductivity is several times lower than that at a standard porosity (cf. Fig. 214). 

In addition to dense sintered alumina, porous alumina materials, i.e. those fired at lower temperatures, are also manufactured for special or less stringent purposes. They are characterized by lower strength. 

Goodfellow Alumina Material Information. http //goodfellow.eom/A/Alumina.html (accessed September 14, 2009). 

D. Hayes, D.W. Budworth and J.P Roberts, Permeability of sintered alumina materials to gases at high temperatures. Trans. Br. Ceram. Soc., 62 (1963) 507-523. 

Nanostructured heterogeneous catalysts were prepared by supporting amines on silica-alumina materials (SA-NR2) via post-modification methodology. The promising adjacent position of acid and base sites on the SA-NR2 allowed high catalytic activity for various organic transformations such as cyanoethoxycarbonylation (Scheme 3.38 route a) and the nitroaldol reaction (Scheme 3.38 route b). ... 

In this case, the temperature reached by alumina/materials-wave interactions is not high enough (80-85°C) to promote an efficient reaction. A small amount of a polar molecule (few drops of DMF) allows a rise in temperature up to 120°C and for a quantitative yield for the microwave-promoted reaction to be obtained. 

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