Magnesia aluminate

Magnesia aluminate (MgAl204) is deposited by combining the two metal chlorides with CO2 and H2 at 950°C as followsit l... 

Y.W. Lee, et al., Study on the mechanical properties and thermal conductivity of silicon carbide-, zirconia- and magnesia aluminate-based simulated inert matrix nuclear fuel materials after cyclic thermal shock../. Nucl. Mater. 319, 15-23 (2003). 

In the vapor phase, acetone vapor is passed over a catalyst bed of magnesium aluminate (206), 2iac oxide—bismuth oxide (207), calcium oxide (208), lithium or 2iac-doped mixed magnesia—alumina (209), calcium on alumina (210), or basic mixed-metal oxide catalysts (211—214). Temperatures ranging... 

The catalysts used in the process are essentially nickel metal dispersed on a support material consisting of various oxide mixtures such as alumina, silica, lime, magnesia, and compounds such as calcium aluminate cements. When the catalyst is made, the nickel is present as nickel oxide which is reduced in the plant converter with hydrogen, usually the 3 1 H2 N2 synthesis gas ... 

Catalysts. - Group VIII metals, conventional base metal catalysts (Ni, Co, and Fe) as well as noble metal catalysts (Pt, Ru, Rh, Pd) are active for the SR reaction. These are usually dispersed on various oxide supports. y-Alumina is widely used but a-alumina, magnesium aluminate, calcium aluminate, ceria, magnesia, pervoskites, and zirconia are also used as support materials. The following sections discuss the base metal and noble metal catalysts in detail, focusing on liquid hydrocarbon SR for fuel cell applications. 

Aksel, C., Davidge, R.W., Knott, P. and Riley, F.L., Mechanical properties of magnesia-magnesium aluminate spinel composites , in III Ceramic Congress Proceedings Book, Engineering Ceramics, Istanbul, Turkey, 2, 172-9, 1996. 

The metal catalysts active for steam reforming of methane are the group VIII metals, usually nickel. Although other group VIII metals are active, they have drawbacks for example, iron rapidly oxidizes, cobalt cannot withstand the partial pressures of steam, and the precious metals (rhodium, ruthenium, platinum, and palladium) are too expensive for commercial operation. Rhodium and ruthenium are ten times more active than nickel, platinum, and palladium. However, the selectivity of platinum and palladium are better than rhodium [1]. The supports for most industrial catalysts are based on ceramic oxides or oxides stabilized by hydraulic cement. The commonly-used ceramic supports include a-alumina, magnesia, calcium-aluminate, or magnesium-alu-minate [4,8]. Supports used for low temperature reforming (< 770 K) are... 

Chemical reactions between solids are used to synthesize mixed powders or complex oxides. The reactants are usually simple oxides, carbonates, nitrates, sulfates, oxalates or acetates, which are mixed according to a target compound with a given stoichiometric composition. An example is the reaction between magnesia and alumina to form magnesium aluminate or spinel, with the following reaction equation ... 

Refractories. Aluminosilicates, silica and aluminous material, basic materials such as magnesite, chrome-bearing materials such as magnesia-chrome bricks, zirconia-bearing materials, and silicon carbide. There are also raw materials such as fireclay, ferrosilicon, and graphite. 

Methane or natural gas steam reforming performed on an industrial scale over nickel catalysts is described above. Nickel catalysts are also used in large scale productions for the partial oxidation and autothermal reforming of natural gas [216]. They contain between 7 and 80 wt.% nickel on various carriers such as a-alumina, magnesia, zirconia and spinels. Calcium aluminate, 10-13 wt.%, frequently serves as a binder and a combination of up to 7 wt.% potassium and up to 16 wt.% silica is added to suppress coke formation, which is a major issue for nickel catalysts under conditions of partial oxidation [216]. Novel formulations contain 10 wt.% nickel and 5 wt.% sulfur on an alumina carrier [217]. The reaction is usually performed at temperatures exceeding 700 °C. Perovskite catalysts based upon nickel and lanthanide allow high nickel dispersion, which reduces coke formation. In addition, the perovskite structure is temperature resistant. 

The integrated planar (IP) SOFC stack concept, for instance, applied by Rolls-Royce Fuel Cell Systems, uses an array of series-connected cells deposited by screen printing onto a flat support tube, a schematic cross section of which is shown Fig. 21.23. The support tube, an inert, porous ceramic, is fabricated from a magnesia magnesium aluminate spinel (MMA), whereby the desired coefficient of thermal expansion is adjusted by the ratio of the base materials [76]. 

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