Aluminum Spinel

Reynen et al. [164] published a seminal account of the synthesis of ceramic powders by the emulsion technique, in which detailed comments were made on the synthesis of Mg-Al spinel particles. Special attention has been paid in this work on the mode of removal of water from ordinary precipitates or emulsions for preparation of particles. In the emulsion method, salts of Mg and Al in the desired molar ratio were dissolved in water, and the solution mixed with an equal amount of alkanes which, depending on the drying method, could be low or high boiling. For ensuring some stability of the emulsion, a surfactant (Span 80 for sulfate solutions and Bry for acetate and formate solutions 0.1-1%) was added. The necessary stirring was accomplished by very high shear forces. 

Hot petroleum drying, found suitable for a variety of powders, was recommended by the authors in view of the simplicity of operation. 

The water extraction method, as used for alumina synthesis by Liu and Mlcox [167], was also successfully used by them for mullite synthesis a mixed colloidal sol of alumina and silica was used as the water phase. 

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The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

The primary reformer consists of a multitude of reformer tubes loaded with the nickel catalyst (15 25% NiO on aluminum oxide, calcium aluminate, or magnesium aluminum spinel support) in a furnace box, in which the heat needed for the reaction is transferred to the tubes by radiation. The heat is generated in burners, generally gas-fired in the furnace box. 

Mechanism of the Promoter Effect. The action of the so-called structural promoters (stabilizers), such as A1203, is closely associated with their solubilities in the iron oxide matrix of the unreduced catalyst or with the capability of the regular crystallizing magnetite to form solid solutions with iron - aluminum spinels [33], [289]-[291]. The solid solutions of Fe304 and the spinel FeAl204 have a miscibility gap below 850 °C... 

Most steam-reforming catalysts are based on nickel as the active material. Also, cobalt and noble metals catalyze the steam-reforming reaction, but they are generally too expensive to find widespread use. A number of different carriers including alumina, magnesium-aluminum spinel, zirconia, and calcium aluminate are employed. 

Residual methane is present at the exit of the combustion zone. In the catalytic bed, the methane steam-reforming and the water shift reactions take place. The gas leaving the ATR reactor is in chemical equilibrium. Normally, the exit temperature is above 900-1100°C. The catalyst must withstand very severe conditions when exposed to very high temperatures and steam partial pressures. One example of an ATR catalyst is nickel supported by magnesium aluminum spinel. For compact design, the catalyst size and shape is optimized for a low pressure drop and high activity. 

E.A. Vasil eva, et al., Specific features of the synthesis of porous materials based on a magnesium-aluminum spinel. Glass Pltys. and Chem. 29(5), 490-493 (2003). 

The spinel group is divided into three immiscible series, the spinel in which Bis aluminum (aluminum-spinel), the chromite (chromium-spinel) series in which B is chromium and the magnetite (iron-spinel) series, in which B is iron. 

S.K. Behera, P. Barpand and S.K. Pratihar, Synthesis of Magnesium-Aluminum Spinel from Autoignition ofNitrate Gel", Mat. Lett., 58, 1451-1455 (2004). 

Villalobos GR, Sanghera JS, Aggarwal ID (2005) Degradation of magnesium aluminum spinel by lithium fluoride sintering aid. J Am Ctaxim Soc 88 1321-1322... 

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