Y-aluminas

Well as various samples of nonporous but amorphous silica. They found that the points fitted on to a common curve very closely, which may be plotted from Table 2.14. A corresponding curve, though based on fewer samples, was put forward for y-alumina. The two curves are close to one another, but the divergence between them is greater than that between different samples of the same substance. Standard isotherm data for argon (at 77 K) on silica have been obtained by various workers. ... 

The microcalorimetric measurements of Della Gatta and his co-workers in their investigation of the interaction of water vapour with highly dehydroxylated y-alumina confirm that in this system also, the nondissocia-tive chemisorption of water is nonactivated, whilst the dissociative chemisorption is always activated. Thus the pseudo-equilibrium between the two chemisorbed states is displaced towards dissociative chemisorption as the temperature is increased above 150 C. 

Allyl Complexes. Allyl complexes of thorium have been known since the 1960s and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a thorium haUde and an aHyl grignard. This synthetic method was utilized to obtain a rare example of a naked aHyl complex, Th(Tj -C2H )4 [144564-74-9] which decomposes at 0°C. This complex, when supported on dehydroxylated y-alumina, is an outstanding heterogeneous catalyst for arene hydrogenation and rivals the most active platinum metal catalysts in activity (17,18). 

Fig. 11. Stmctural model of the (111) face of y-alumina (53). The small soHd circles represent, the large open circles OH groups, and the hatched...

Hydrodesulfurization. A commercial catalyst contains about 4 percent CoO and 12 percent M0O3 on y-alumina and is presulfided before use. Molybdena is a weak catalyst by itself and the cobalt has no catalytic action by itself. 

Figure 5 Solid state NMR spectra of Vanadium oxide on y-alumina as a function of vanadium loading (wt.%) and surface coverage 0. Note the gradual emergence of the six-coordinated vanadium site with increased loading.

Eigure 3.56 depicts LEIS spectra for two completely different types of AI2O3 sample, i. e. a-alumina (sapphire) and y-alumina (a powder with high specific surface area) which show very similar results in both cases after thermal treatment at 400 °C [3.142]. Reduction of the A1 signal in y-alumina was ascribed to shielding by hydroxyl groups formed by water molecules, which are typical adsorbates on y-alu-mina. 

Geminal difluorides usually require a strong base for conversion to vinylic fluorides, but some aluminum oxides such as neutral y-alumina or Woelm alumi-... 

CASE STUDY INORGANIC ZIRCONIA y-ALUMINA-COATED MEMBRANE ON CERAMIC SUPPORT... 

The advantage of sol-gel technology is the ability to produce a highly pure y-alumina and zirconia membrane at medium temperatures, about 700 °C, with a uniform pore size distribution in a thin film. However, the membrane is sensitive to heat treatment, resulting in cracking on the film layer. A successful crack-free product was produced, but it needed special care and time for suitable heat curing. Only y-alumina membrane have the disadvantage of poor chemical and thermal stability. 

The vast increase in the application of membranes has expanded our knowledge of fabrication of various types of membrane, such as organic and inorganic membranes. The inorganic membrane is frequently called a ceramic membrane. To fulfil the need of the market, ceramic membranes represent a distinct class of inorganic membrane. There are a few important parameters involved in ceramic membrane materials, in terms of porous structure, chemical composition and shape of the filter in use. In this research, zirconia-coated y-alumina membranes have been developed using the sol-gel technique. 

Figure 16.23 presents the alumina-coated ceramic membrane. There were opportunities to fabricate a crack-free ceramic membrane coated with y-alumina. The supported zirconia-alumina membrane on the ceramic support shows an irregular surface. The non-uniform surface of ceramic support causes the irregular surface on the top layer of the membrane. Some of the membrane sol was trapped in the porous ceramic support during coating, and caused the irregularity of the membrane surface. 

Aluminum oxide, A1203, is known almost universally as alumina. It exists with a variety of crystal structures, many of which form important ceramic materials (see Section 14.22). As a-alumina, it is the very hard, stable, crystalline substance corundum impure microcrystalline corundum is the purple-black abrasive known as emery. Some impure forms of alumina are beautiful, rare, and highly prized (Fig. 14.25). A less dense and more reactive form of the oxide is y-alumina. This form absorbs water and is used as the stationary phase in chromatography. 

The cycloaddition reactions of unsaturated esters with cyclopentadiene on y-alumina [18]... 

The phosphorescence lifetimes for the p-aminobenzoic acid anion adsorbed on sodium acetate as a function of temperature were evaluated in a manner similar to the one discussed by Oelkrug and coworkers (,28-30) for polycyclic aromatic hydrocarbons adsorbed on y-alumina. In general, the solid-surface phosphorescence lifetime cutrves for the anion of p-aminobenzoic acid followed Equation 2. 

Bimetallic Co-Mo oxide specimens were prepared via co-impregnation of calculated amounts of cobalt nitrate and ammonia heptamolybdate on y-alumina to achieve a total metal loading of 20wt% with an equimolar Co Mo ratio. Nitridation of catalysts was carried in a fixed bed... 

Investigation of ozonolysis of phenol using y-alumina based catalysts... 

A mixed solution of platinum and ruthenium precursors was prepared by adding H2PtCl6 and RuClj at a certain ratio to de-ionized water. The solution was in negnated on y-alumina of size 300-... 

Alumina, present in the gamma modification, is the most suitable high surface area support for noble metals. The y-Al203 in washcoats typically has a surface area of 150-175 m g However, at high temperatures y-alumina transforms into the alpha phase, and stabilization to prevent this is essential. Another concern is the diffusion of rhodium into alumina, which calls for the application of diffusion barriers. 

Figure 5. Typical EDS analysis of a 4nm cluster of Fe on y alumina In the chlorlded form taken at. 20 Mx for 200 sec.

Alumina - Alumina forms a variety of oxides and hydroxides whose structures have been characterized by X-ray diffraction (16). From the catalytic viewpoint y-alumina is the most important. This is a metastable phase that is produced from successive dehydration of aluminum trihydroxide (gibbsite) to aluminum oxide hydroxide (boehmite) to y-alumina, or from dehydration of boehmite formed hydrothermally. y-alumina is converted into a-alumina (corundum) at temperatures around 1000 C. 

Further dehydration of boehmite at 600 0 produces y-alumina, whose spectrum is shown in Figure 3b. There is a loss in surface area in going from boehmite to y-alumina. The sample shown here has a surface area of 234 m /g (this sample was obtained from Harshaw A23945 the calcined Kaiser substrate gave an identical infrared spectrum). The y-alumina sample shows two major differences from o-alumina. First, there is a more intense broad absorption band at 3400 cm" due to adsorbed water on the y-alumina. Second, the y-alumina does not show splitting of the phonon bands between 400 and 500 cm" as was observed for o-alumina. The y-alumina is a more amorphous structure and has much smaller crystallites so the phonon band is broader. The y-alumina also shows three features at 1648, 1516 and 1392 cm" due to adsorbed water and carbonate. 

The features due to adsorbed water and carbonates observed on the boehmite and y-alumina deserve further attention as they differ from results published by previous investigators. Figure 4 shows a series of difference spectra for adsorption on y-alumina. Spectra were taken after drying the y-alumina at 350 C, cooling to room temperature and carrying out room temperature adsorption. The spectra are the difference of the sample before and after adsorption. Spectrum 4e is the spectrum for the as received alumina differenced with the dried alumina. The positive band at 3400 cm" is due to adsorbed water, and the small negative feature at 3740 cm" is due to isolated hydroxyls on the dried surface. Besides the three... 

The results obtained for the various aluminum oxides and hydroxides indicate that infrared photoacoustic spectroscopy may be useful in characterizing structural transformations in these species. Very clear differences between a-alumina and y-alumina were noted in the region of the lattice vibrations. The monohydrate, boehmite, showed a very distinct Al-OH stretching feature at 1070... 

A commercial pectinase, immobilised on appropriately functionalised y-alumina spheres, was loaded in a packed bed reactor and employed to depolymerise the pectin contained in a model solution and in the apple juice. The activity of the immobilized enzyme was tested in several batch reactions and compared with the one of the free enzyme. A successful apple juice depectinisation was obtained using the pectinase immobilised system. In addition, an endopolygalacturonase from Kluyveromyces marxianus, previously purified in a single-step process with coreshell microspheres specifically prepared, was immobilised on the same active support and the efficiency of the resulting catalyst was tested. 

The Pectolyase Y-23 and the purified yeast PG were immobilised as described by Coletti-Previero et al. [14]. 5 g of y-alumina spheres, previously equilibrated in 200 ml of a buffered solution at pH 6.0, was treated first with 30 ml of 0.04 M o-phosphorylethanolamine and then with 30 mL of 0.56 M glutaraldehyde. These two reactions were performed at 25 C and pH 6.0, for 1.5 h and were followed by several washings with abundant distilled water. Finally, 15 mL of 10 mg/mL Pectolyase Y-23 solution or 25 mL of 0.5 mg/mL of purified yeast PG solution, both buffered at pH 6.0, were added and left to react for 2 h at 25 C. y-alumina spheres were then washed with 450 mL of distilled water. The reaction solution was tested for protein content and enzymatic activities. 

Pulp from ripe Golden apple was pressed in a mortar and filtered, thus obtaining a cloudy and dense juice. Potassium metabisulphite was added as antioxidant at a final concentration of 0.15 mg/mL. The pH of the prepared apple juices was 4.1 4.3. Depectinisation experiments were carried out loading the juice in the packed bed reactor and recycling for 30 min at 25 "C. The reaction mixture was then collected and the percentage reduction of viscosity measured as above described. The y-alumina spheres were abundantly washed with distilled water before performing the successive batch reaction. 

---