Alloy synthesis catalysts

M.M. Ermilova, N.V. Orekhova, L.S. Morozova, and E.V. Skakunova, Selective hydrogenation of cyclopolyolefines on membrane catalyst from palladium-ruthenium alloy. Membrane Catalysts Permeable to Hydrogen and Oxygen, Moscow, Topchiev Inst, of Petrochemical Synthesis, 1985, p. 70. 

In some cases a catalyst consists of minute particles of an active material dispersed over a less active substance called a support. The active material is frequently a pure metal or metal alloy. Such catalysts are called supported catalysts, as distinguished from unsupported catalysts, whose active ingredients are major amounts of other substances called promoters, which increase the activity. Examples of supported catalysts are the automobile-muffler catalysts mentioned above, the platinum-on-alumina catalyst used in petroleum reforming, and the vanadium pentoxide on silica used to oxidize sulfur dioxide in manufacturing sulfuric acid. On the other hand, the platinum gauze for ammonia oxidation, the promoted iron for ammonia synthesis, and the silica-alumina dehydrogenation catalyst used in butadiene manufacture typify unsupported catalysts. 

The performance of these novel catalysts was compared with that of a conventional copper-zinc-alumina methanol synthesis catalyst under the same conditions (250°C, 40,000 h, 72 /28 CO, 5 MPa). The methanol yield was only 8.0 g mol/l/hr which was more than an order of magnitude less than that obtained with the catalyst produced from the Cu-Ce-Al alloy. The methanol yields obtained using the Cu-Ce catalysts and the 72 /28 CO syngas were comparable to those obtained using conventional catalysts with CO2 present in the feed. 

Strasser et al. [59, 67, 91-94] recently apphed a freeze-diying technique in the synthesis of ft alloy nanoparticle catalysts with enhanced ORR activity. The ft-Cu alloy catalyst after electrochemical dealloying was reported to have both mass and specific activities about four to six times those of a standard commercial Pl/C catalyst, in both RDE and MEA tests. The synthesis involved an impregnati(Mi/freeze-diying route followed by annealing. Preparation started with impregnation and smiication of... 

Shaijumon MM, et al. Synthesis of multi-walled carbon nanotubes in high 3deld using Mm based AB2 alloy hydride catalysts and the effect of purificatian on their hydrogen adsorption properties. Nanotechnology 2005 16(4) 518-24. 

In the early research stages of ammonia synthesis catalyst, Mittasch et al. studied almost all metal elements and their bimetallic alloy in the Periodic Table. Several metals have no or less catal3dic functions themselves. However, the addition of some promoter could increase their activities. The addition of a secondary metal into Fe, Mo, W, Co, Ni, Pd, Pt, Os, Mn enhances their activities. The different ratio between two metals leads to a different activity. It can be concluded from these results that the addition of metals in Vlff or VI groups favors enhancing of iron-based catalyst activity. For example, Fe-Mo (1 1) catalyst has high activity. If the Mo content is less than 80%, the activity decreases after running for a long-time. These catalysts are prepared by calcinations of metal nitrates and ammonium molybdate... 

Virtually all commercial HPHT synthesis of diamond uses iron, nickel, cobalt, manganese, chromium, and their alloys as catalyst-solvents. However, many other metals ean catalyze graphite-to-diamond formation at higher temperatures and pressures, as can water, silicates, and other minerals that are more akin to the environment in which natural diamonds grow in the earth. 

The main uses of palladium [13] are in the electronics and electrical industries, in circuitry and in dental alloys. It finds many catalytic applications in industry, as well as in diffusion cells for the synthesis of hydrogen, and in automobile catalysts. Jewellery and three way auto-catalysts are the principal uses of platinum, which fulfils a wide range of roles in the chemical industry. 

ZnO is, apparently, a very suitable support for the copper particles. Evidence exists, however, that its role does not have to be limited to that of a support only. Nakamura et al. have studied the influence of Zn on methanol synthesis on copper crystals by depositing Zn on the surface [J. Nakamura, I. Nakamura, T. Uchijima, Y. Kanai, T. Watanabe, M. Saito, and T. Fujitani, J. Catal. 160 (1996) 65]. They found that the rate was enhanced by a factor of six (see Fig. 8.14), suggesting that Zn atoms also act as a chemical promoter. Whether some of the ZnO in the real catalyst is actually reduced to such a degree that it can alloy into the copper particles and segregate to the surface, as suggested by Nakamura, is still a controversial topic. 

Fe, and B SI, Tl, Th, and Ce). The transforaed materials exhibit high specific activity In methanation, ammonia synthesis, and ethylene hydrogenation reactions. The similarity between the industrial methanation catalysts and catalysts obtained by decomposition of various Intermetallics Is striking. Most catalysts obtained by decomposition of a binary alloy Involve an associative combination of... 

Xin and co-workers modified the alkaline EG synthesis method by heating the metal hydroxides or oxides colloidal particles in EG or EG/water mixture in the presence of carbon supports, for preparing various metal and alloy nanoclusters supported on carbon [20-24]. It was found that the ratio of water to EG in the reaction media was a key factor influencing the average size and size distribution of metal nanoparticles supported on the carbon supports. As shown in Table 2, in the preparation of multiwalled carbon nanotube-supported Pt catalysts... 

The small metal particle size, large available surface area and homogeneous dispersion of the metal nanoclusters on the supports are key factors in improving the electrocatalytic activity and the anti-polarization ability of the Pt-based catalysts for fuel cells. The alkaline EG synthesis method proved to be of universal significance for preparing different electrocatalysts of supported metal and alloy nanoparticles with high metal loadings and excellent cell performances. 

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