Platinum-5 molybdenum

Palladium electrocatalysts, 183 Palladium-alloy electrocatalysts, 298-300 Pareto-optimal plot, 85 Platinum-alloy electrocatalysts, 6, 70-71, 284-288, 317-337 Platinum-bismuth, 86-87, 224 Platinum chromium, 361 362 Platinum-cobalt, 71, 257-260, 319, 321-330, 334-335 Platinum-iron, 319, 321, 334-335 Platinum-molybdenum, 253, 319-320... 

Stable zirconium, platinum, molybdenum, and tungsten complexes of cyclooctyne, a zirconium complex of cydoocta-5-enyne, and a bimetallic molybdenum complex of cyclocta-3,7-dienyne have been discussed in earlier reviews.28 More recently, two stable zirconocene complexes of cycloocta-trienyne (275 and 276) have been prepared101 by /3-hydride elimination from 274 in the presence of PMe2R [Eq. (45)]. 

Figure 11 (A) Stripping voltammetry (20 m Vs at 55 °C) of CO layers on humidified PEM fuel-cell anodes (1) platinum catalyst (2) platinum/molybdenum catalyst. Voltammetry in the absence of adsorbed CO on the platinum/molybdenum catalyst is shown in (3). Molybdenum-mediated electro-oxidation of adsorbed CO takes place on the alloy catalyst in the peak at 0.45 V and at lower overpotentials [79]. (B) Steady-state polarization curves of PEM fuel-cell anode at 85 °C for platinum (squares) and platinum/molybdenum catalysts in the presence of 100 ppm CO (filled points) and pure H2 (unfilled points). (From Ref 79.)... 

At temperatures below about 125°C, CO adsorption on platinum is very strong. Even few ppms in the H2 stream cause substantial performance losses on the anode. Therefore, the use of platinum alone is not viable for HOR in the presence of CO in low temperature fuel cells. Thus, platinum-ruthenium, platinum-molybdenum and platinum-tin are being used as anode electrocatalysts for hydrogen oxidation in the presence of CO because they tolerate low ppms of CO without excessive polarization losses. Timgsten carbide (WC) also shows high CO-tolerance [38,44]. 

Kariya et al. performed dehydrogenation of methylcyclohexane and other cycloalkanes over platinum, palladium and rhodium monometallic and platinum/palladium, platinum/rhodium, platinum/molybdenum, platinum/tungsten, platinum/rhenium platinum/osmium and platinum/iridium catalysts supported on both petroleum coke active carbon and on alumina between 375 and 400 °C [279]. The platinum catalyst supported by petroleum active carbon showed the highest activity. While platinum was the most active monometallic catalyst, its activity could be increased by addition of molybdenum, tungsten and rhenium. 

Zhang H, Wang Y, Fachini ER, Cabrera CR. Electrochemically codeposited platinum/molybdenum oxide eleetrode for eatal3hic oxidation of methanol in acid solution. Electrochem Solid State 1999 2 437-9. 

The type of anode catalyst has a strong effect on the severity of CO poisoning, since the catalyst affects the kinetics of CO adsorption (equation (2.12) and equation (2.13)) and CO oxidation (equation (2.18) and equation (2.19)). Based on these mechanisms, many CO-tolerant electrocatalysts have been developed by Pt alloying, such as PtRu (platinum/ruthenium) [24,38], PtSn (platinum/tin) [39-41], and PtMo (platinum/molybdenum) [42-44]. Generally, alloying Pt with a second element can enhance the catalytic activity of the Pt through one or more of the following effects ... 

A great number of norbornene-like monomers [e.g., m = 1-3, R] and R2 = alkyl and aryl groups, Eqs. (103) and (104)] with or without substituents have been employed in polymerization reactions induced by Ziegler-Natta and ROMP catalysts derived from ruthenium, osmium, iridium, palladium, platinum, molybdenum, and tungsten halides or vanadium and zirconium halides or acetylacetonate associated with organometallic compounds [162, 163]. Both addition and ring-opened polymers have been obtained by this way depending on the catalyst employed [Eqs. (103) and (104)]. 

The photochemistry of dithiolene complexes of selected second- and third-row transition metal ions have also been investigated. Like the complexes with nickel, dithiolene complexes of palladium, platinum, molybdenum, and tungsten catalyze the formation of hydrogen from water when aqueous solutions of the complexes are irradiated at wavelengths shorter than 290 Tetrahydrofiiran is... 

Diffusion bonding eliminates any foreign material as needed in brazing so it would be preferred for implantable medical device applications. Alumina can be diffusion bonded to a few biocompatible metals including tungsten, platinum, molybdenum, stainless steel, and niobium [58,61]. Zirconia has been successfully diffusion... 

Catalytic hydrogenation requires a catalyst such as nickel, copper, platinum, molybdenum, or tungsten. These catalysts usually are supported on other materials and are especially prepared for the type of reduction to be carried out. Reduction conditions vary widely, depending on the nature of the nitro compound and the catalyst. Reduction may be carried out in solvent in the vapor phase or in the liquid phase. Aniline can be made by continuous vapor-phase reduction of nitrobenzene at 350 to 460°C at nearly atmospheric pressure. Some reductions, on the other hand, are run at 1000 to 4000 psi. 

The increased activity of platinum - molybdenum alloys is evidently due to a change in the general course of the reaction [193, 240]. Addition of molybdenum (on account of its ready dissolution in acidic solutions and the possibility of change in the valence state of the ions) can lead to formation of a redox system (Mo " "— Mo ) near the electrode, and this leads to a change in the course of the reaction. This point of view is confirmed by the fact that oxidation of methanol and formaldehyde is accelerated by molybdate ions [245]. Shropshire [245] proposed the following scheme to explain this effect ... 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

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. 

In past years, metals in dilute sulfuric acid were used to produce the nascent hydrogen reductant (42). Today, the reducing agent is hydrogen in the presence of a catalyst. Nickel, preferably Raney nickel (34), chromium or molybdenum promoted nickel (43), or supported precious metals such as platinum or palladium (35,44) on activated carbon, or the oxides of these metals (36,45), are used as catalysts. Other catalysts have been suggested such as molybdenum and platinum sulfide (46,47), or a platinum—nithenium mixture (48). 

Heating and Cooling. Heat must be appHed to form the molten zones, and this heat much be removed from the adjacent sohd material (4,70). In principle, any heat source can be used, including direct flames. However, the most common method is to place electrical resistance heaters around the container. In air, nichrome wine is useflil to ca 1000°C, Kanthal to ca 1300°C, and platinum-rhodium alloys to ca 1700°C. In an inert atmosphere or vacuum, molybdenum, tungsten, and graphite can be used to well over 2000°C. 

In catalytic toluene hydrodealkylation, toluene is mixed with a hydrogen stream and passed through a vessel packed with a catalyst, usually supported chromium or molybdenum oxides, platinum or platinum oxides, on siHca or alumina (50). The operating temperatures range from 500—595°C... 

Cesium does not alloy with or attack cobalt, iron, molybdenum, nickel, platinum, tantalum, or tungsten at temperatures up to 650°C (35). 

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