Metal metallic glass catalysts

While this decomposition reaction is slow at room temperature, the disproportionation process can be accelerated by heat, certain catalysts (e.g., metal ions), and light. Traces of alkali metal ions are normally present in aqueous solutions stored in glass bottles, so plastic or wax-coated glass containers reduce the concentration of metal ion catalysts. Brown-colored containers limit the wavelengths of light that can be absorbed by the solution, restricting the initiation of the disproportionation reaction. 

The precursor alloy is quenched to form small grains readily attacked by the caustic solution [31], Quenching can also enable specific intermetallic phases to be obtained, although this is less common. Yamauchi et al. [32-34] have employed a very fast quench to obtain a supersaturation of promoter species in the alloy. It is even possible to obtain an amorphous metal glass of an alloy, and Deng et al. [35] provide a review of this area, particularly with Ni, Ni-P, Ni-B, Ni-Co, and Ni-Co-B systems. The increased catalytic activity observed with these leached amorphous alloy systems can be attributed to either chemical promotion of the catalyzed reaction or an increased surface area of the leached catalyst, depending on the components present in the original alloy. Promotion with additives is considered in more detail later. 

Amorphous (rapidly quenched) metals and alloys have been investigated as catalysts (Schlogl, 1985). It has been found that adsorption characteristics of carbon monoxide on metallic glasses are different from those on crystalline materials. For example CO is found to dissociate readily on the surface of Ni76Bi2Si,2 metglass, but it is always molecularly adsorbed on metallic nickel (Prabhakaran Rao, 1985). 

Samarium 62 Sm Reactor control and neutron shielding, magnets, luminescent and infra-red absorbing glasses, catalysts, ceramics, electronic devices, magnetostrictive alloys, misch metal... 

CRMs in the area of technical and industrial materials (e.g., pure metals, alloys, catalysts for cars, semiconductors, fossil fuels, glasses, plastics)... 

Use For metalizing glass and plastic catalyst in pharmaceuticals, resins, petrochemicals, solder, tanning agent, and food and beverage preservative. 

Metallic glasses have been used in catalysis in two ways, namely, in investigations carried out on as-quenched glassy metals and in those where the glassy metals were subjected to different pretreatments and served merely as precursors to catalytically active materials. The use of glassy metals as catalyst precursors has been shown to open up new possibilities for the preparation of supported metal catalysts with unusual chemical and structural properties. This potential resides mainly on the high reactivity and isotropic nature of these materials compared to their crystalline counterparts. Several efficient supported metal catalysts are compared to conventionally prepared supported metal catalysts in Chap. 3. 

Various supported metal catalysts [4.20,44,64,65] were prepared by oxida-tion/reduction treatment of the metallic glass precursor. The oxidation be-... 

The BET surface area as well as the palladium metal surface area of the precursor increases by more than two orders of magnitude during the in situ activation. The solid-state reactions occurring in the metallic glass during in situ activation result in a large increase of the BET surface area from 0.02 to 45.5 m2/g. The palladium metal surface area of the as-prepared catalyst determined by CO chemisorption is 6.9m2/g, which corresponds to a palladium dispersion of about 6%. 

The thermal stability is a severe limitation if the metallic glass is to be used in as-quenched state for catalysis however, that is not necessarily the case if the glassy alloy is used as catalyst precursor. The thermal stability is mainly influenced by the chemical composition of the metallic glass and the medium to which it is exposed. It has been shown that the crystallization temperature can be significantly lowered in the presence of a hydrogen atmosphere [4.23,24,31,50] or an adsorbed organic compound [4.76]. 

The bulk oxidation generally leads to large stresses in the materials due to the differences in the specific volumes of the unreacted part of the alloy and the oxidized part of the material. This stress eventually results in embrittelment of the material, a behavior which has to be accounted for if catalysts are prepared by oxidation of metallic glass precursors. 

Despite the rather short period since the attention of catalytic chemists turned to metallic glasses as catalysts, there have already been a remarkable number of publications, and there are already some rather well-studied reactions and catalysts. These studies led to the identification of the probable active phases of certain transformations, disclosed the way they... 

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