Tungsten/nickel systems

The adsorption of CO on nickel has received extensive study since large area nickel films are comparatively simple to prepare. The nickel system therefore offered the possibility of producing a clean surface on a metal crystallizing with a face centered cubie structure. The results obtained on this surface could then be compared with those measured on tungsten, which crystallizes with a body centered,cubic structure. Much of the earlier work carried out for CO adsorption on the elements nickel, palladium, and platinum was reviewed by Gundry and Tompkins in 1960 135). 

Herein we report more details on our preliminary report (24) of C-F activation at tungsten(0) including its extension to molybdenum and nickel systems as well as qu itative observations concerning the mechanism of these transformations. 

To improve the darkening characteristics of the device, a reservoir film that also darkens can be incorporated into the system. One material examined is hydrated nickel oxide. This is able to store Li reversibly and becomes darker when it is depleted, enhancing the darkening effect of the tungsten bronze layer. 

Tunable uv-vis lasers, 23 144 Tuneable separation systems, 22 654 Tung oil, 9 143, 149, 150, 20 814-817 Tungstate catalysts, 22 48 Tungstates, 25 381-382 properties of, 25 382t Tungsten (W). See Nickel-chromium-molybdenum (tungsten) alloys, 25 349-376... 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Trapnell 79) has reviewed the work on these systems prior to 1962 and has attempted to interpret all the available information in the light of these mechanisms. Most of the pertinent earlier measurements were made on tungsten or nickel. Two of the most important observations are (1) that exchange on these metals is rapid even at temperatures below —100° and (2) that the order of the reaction with respect to the hydrogen pressure is eonsiderably less than unity (0.3-0.6). 

There has been to some degree the belief that Mossbauer spectroscopy, although in principle an ideal technique for catalyst studies, for practical purposes can only be applied to problems in catalysis if the catalyst contains either iron or tin. Therefore, one of the main purposes of this review is to show how Mossbauer spectroscopy can be directly extended to many additional Mossbauer atoms or isotopes (such as antimony, europium, nickel, ruthenium, gold, and tungsten) and, perhaps more importantly, how the technique can be extended to obtain information about systems that do not contain a Mossbauer atom. ... 

Asymmetric allylboration, characteristics, 9, 197 Asymmetric allylic alkylation, allylic alcohols with copper, 11, 99 with iridium, 11, 105 with molybdenum, 11, 109 with nickel, 11, 102 with non-palladium catalysts, 11, 98 with platinum, 11, 103 reaction systems, 11, 112 with rhodium, 11, 104 with ruthenium, 11, 108 with tungsten, 11, 111... 

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