Nickel-gold catalysts

A third factor controlling surface composition is the atmosphere in which the catalyst is used. The surface will be enriched in that component of the alloy that has the highest heat of adsorption of the gas. In an oxygen atmosphere the surface of a nickel-gold catalyst becomes enriched with nickel rather than gold. 57 In the presence of CO the surface of a palladium-silver alloy becomes enriched with palladium while, normally, silver would be the predominant surface component. 58 This enrichment of the surface by palladium should also be observed in a hydrogen atmosphere. 

The NHCs have been used as ligands of different metal catalysts (i.e. copper, nickel, gold, cobalt, palladium, rhodium) in a wide range of cycloaddition reactions such as [4-1-2] (see Section 5.6), [3h-2], [2h-2h-2] and others. These NHC-metal catalysts have allowed reactions to occur at lower temperature and pressure. Furthermore, some NHC-TM catalysts even promote previously unknown reactions. One of the most popular reactions to generate 1,2,3-triazoles is the 1,3-dipolar Huisgen cycloaddition (reaction between azides and alkynes) [8]. Lately, this [3h-2] cycloaddition reaction has been aided by different [Cu(NHC)JX complexes [9]. The reactions between electron-rich, electron-poor and/or hindered alkynes 16 and azides 17 in the presence of low NHC-copper 18-20 loadings (in some cases even ppm amounts were used) afforded the 1,2,3-triazoles 21 regioselectively (Scheme 5.5 Table 5.2). 

This is not exactly what the speaker had in mind In 2007, we are faced with the potential severity of the problem encapsulated by the cartoon what is as yet not clear is whether STM might provide the necessary molecular insight to designing an appropriate catalyst just as the Aarhus Topsoe group achieved in their development of the nickel gold steam-reforming catalyst. 

The metal cap may influence the measurements. Various metal cap materials have been used, including the standard nickel, gold-plated nickel, or, more recently, silicon-coated nickel. Nickel is a good catalyst for carbon formation, and the measurements may therefore be falsified by carbon formation on the metal cap. Oxidation of reduced nickel results in similar problems. The experience with the recently developed silicon-coated caps is more promising. 

NICKEL, COBALT, COPPER, MANGANESE AND GOLD CATALYSTS... 

Catalyst development and catalyst/ microreactor integration. Several ATR, WGS, and PrOx catalysts have been prepared. The ATR catalysts include beta-alumina supported nickel. These catalysts are being evaluated. Transition metal carbide and oxide supported gold catalysts were demonstrated to be highly active for the WGS... 

The faster kinetics of alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells opens up the possibility of using less expensive Pt-free catalysts, as nickel, gold, palladium and their alloys [30]. Thus, the cost of ADAFC could be potentially lower compared to the acid DAFC technology if non-precious metal alloys are used for the alcohol electrooxidation, being the nanoparticulated Ni-Fe-Co alloys developed by Acta (Italy) with the trade name of HYPERMEC a good example. 

Mesoporous silicates serve as the most suitable host for the gold NPs with the size of 2 mn. The cyclohexane conversion may reach 20-30% at the selectivity to cyclohexanol up to 95%, unlike the commercial nickel naphthenate catalysts (conversion 4%, selectivity 70-85%). 

Silver-containing catalysts are used exclusively in all commercial ethylene oxide units, although the catalyst composition may vary considerably (129). Nonsdver-based catalysts such as platinum, palladium, chromium, nickel, cobalt, copper ketenide, gold, thorium, and antimony have been investigated, but are only of academic interest (98,130—135). Catalysts using any of the above metals either have very poor selectivities for ethylene oxide production at the conversion levels required for commercial operation, or combust ethylene completely at useful operating temperatures. 

In order that the possibility of contamination of catalysts with traces of oxides could be eliminated Campbell and Emmett (51) studied the catalytic activity of metallic films of nickel and its alloys with copper or gold. They were deposited under a high vacuum and then sintered (alloys also homogenized) in hydrogen at 5 cm Hg pressure at 350°C or 500°C. The films were subsequently allowed to cool to room temperature and only... 

Hardy and Linnett (59) studied the heterogeneous recombination of atomic hydrogen at room temperature on nickel and nickel alloy foils. They did not find any similarity to the behavior of palladium and its alloys with gold studied earlier (35). There was no evidence that, as a result of exposure to atomic hydrogen, hydride was formed in any metal catalyst investigated with a resulting change in the activity of the initial parent metal catalysts. 

Nickel catalysts used in steam reforming are more resistant to deactivation by carbon deposition if the surface contains sulfur, or gold. Explain why these elements act as promoters. Would you prefer sulfur or gold as a promoter Explain your answer. 

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