Alumina stability

Fe/Ir catalysts on silica and alumina Fe and Ir Mossbauer spectroscopy silica- and alumina-supported Fe-Ir catalysts formed by calcination in air contain mixtures of small particles of Fe(III) oxide and Ir(IV) oxide. IrOz is reduced in hydrogen to metallic Ir. a-Fe203 on SiOz is reduced in hydrogen to an Fe-Ir alloy, whilst supported on alumina stabilizes in hydrogen as Fe(II). Possible use for methanol formation is discussed... 

Attia, A. Zukalova, M. Rathousky, J. Zukal, A. Kavan, L. 2005. Mesoporous electrode material from alumina-stabilized anatase Ti02 for lithium ion batteries. J. Solid State Electrochem. 9 138-145. 

Pure chromia gel is always converted to the a-oxide, and its low catalytic activity is due to its low surface area. Addition of alumina stabilizes high-area j-phase solid solutions in freshly reduced coprecipitated catalysts, but on regeneration by heating in air, the high Cr203 content portions of such catalysts are converted to the a-phase with some loss of area and of catalytic activity. 

Media Small pieces of material used inside a mill jar to increase mixing energy and efficiency. Commonly used materials include alumina, stabilized zirconia, flint pebbles, steel, chrome-plated steel, boron carbide, silicon carbide, and plastic-coated versions of these. Common shapes include spherical, cylindrical, radius-end cylinders, and long rods. Sizes range from 1 mm or less to over 5 cm. 

Although on alumina the Pt loading varied between 0.3 wt-% and 2.0 wt. %, the Pt dispersion on alumina changed randomly between 23 % and 40 %, i.e., no dependency on loading was observed. The average dispersion amounted to about 30 % for nitrogen-decomposed as well as for air-decomposed samples. The preferred stence of dispersed, alumina-stabilized Pt was confirmed by CO adsorption states as observed by DRIFTS [4], The stabilization of dispersed Pt on AI2O3 may be tentatively ascribed to the Lewis acidity of the support by which the mobility of surface metal species is limited. Since donor-acceptor interactions between deposited Pt and Al sites may exist and result in support stabilisation of Pt, all the other preparation conditions are obviously overruled [S]. 

X-ray studies of two systems prepared with the same alumina samples by the same procedure and calcined at the same conditions allow us to conclude that alumina stabilization by Ce is weaker than by La [49]. The formation of the solid solution based on the y-alumina structure by substitution of AP+ on La + ions imposes limitations on the transitions to 5, 0, a-alumina. Alumina modified by Ce does not show essential stabilization of the structure of alumina. This is caused by the limitations on alumina interaction with Ce ions. 

Mchale J M ef a/1996 Surface energies and thermodynamic stability in nanocrystalline aluminas Science 277 788... 

The magnesia and alumina suspension is prepared by treatment of an aqueous solution, containing aluminum and magnesium salt in the desired proportion, with sodium hydroxide. The coprecipitated aluminum and magnesium hydroxides are collected by filtration, washed free of soluble salts, and stabilized by the addition of a suitable hexatol. 

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). 

Ceramics (qv) such as those in Table 12 find high temperature use to over 800°C (32). Advanced ceramics finding interest include alumina, partially stabilized zitconia, siUcon nitride, boron nitride, siUcon carbide, boron carbide, titanium diboride, titanium carbide, and sialon (Si—Al—O—N) (33) (see... 

Most catalyst supports are simply nearly inert platforms that help stabilize the dispersion of the catalyticaHy active phase. Sometimes, however, the supports play a direct catalytic role, as exemplified by the alumina used in supported Pt and RePt catalysts for naphtha reforming. 

In addition to platinum and related metals, the principal active component ia the multiflmctioaal systems is cerium oxide. Each catalytic coaverter coataias 50—100 g of finely divided ceria dispersed within the washcoat. Elucidatioa of the detailed behavior of cerium is difficult and compHcated by the presence of other additives, eg, lanthanum oxide, that perform related functions. Ceria acts as a stabilizer for the high surface area alumina, as a promoter of the water gas shift reaction, as an oxygen storage component, and as an enhancer of the NO reduction capability of rhodium. 

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

Butylated Hydroxyanisole. 2- and 3-/ i -Butyl-4-methoxyphenol (butylated hydroxyanisole (BHA)) is prepared from 4-methoxyphenol and tert-huty alcohol over siUca or alumina at 150°C or from hydroquinone and tert-huty alcohol or isobutene, using an acid catalyst and then methylating. It is widely used in all types of foods such as butter, lard, and other fats, meats, cereals, baked goods, candies, and beer as an antioxidant (see Antioxidants Eood additives). Its antioxidant properties are not lost during cooking so that flour, fats, and other BHA-stabiLized ingredients may be used to produce stabilized products. 

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