Mechanisms proposed dissociative, with

Subsequent studies have failed to support the carbide theory, and it is now generally accepted that carbides of the type proposed by Craxford play little or no part in the Fischer-Tropsch synthesis (86, 87). It has, however, recently been suggested, by analogy with the mechanism proposed for the Haber synthesis of ammonia, that carbides formed by dissociative absorption of carbon monoxide would be expected to be readily hydrogenated and could therefore be of importance in Fischer-Tropsch synthesis over heterogeneous catalyst (88). 

Another mechanism of nitroxyl radical regeneration was proposed and discussed in the literature [67-71]. The alkoxyamine AmOR is thermally unstable. At elevated temperatures it dissociates with cleavage of the R—O bond, which leads to the appearance of an [AmO + R ] radical pair in the cage of polymer. The disproportionation of this radical pair gives hydroxylamine and alkene. The peroxyl radical reacts rapidly with hydroxylamine thus... 

Fahey (16) suggests that intermediate 3 dissociates formaldehyde he finds supportive evidence in the rhodium-based system by observation of minor yields of 1,3-dioxolane, the ethylene glycol trapped acetal of formaldehyde. For reasons to be discussed later, we believe the formation of free formaldehyde is not on the principal reaction pathway. (c) We have also rejected two aspects of the reaction mechanism proposed by Keim, Berger, and Schlupp (15a) (i) the production of formates via alcoholysis of a formyl-cobalt bond, and (ii) the production of ethylene glycol via the cooperation of two cobalt centers. Neither of these proposals accords with the observed kinetic orders and the time invariant ratios of primary products. 

Evidence for dissociative chemisorption comes from several sources (8,19-21). TPD studies conducted with Rh single crystals (19-21) suggest that a portion of the NO adsorbed at ambient temperatures occurs dissociatively. Further dissociation is presumed to occur at elevated temperatures since N2 and N2O are observed during TPD at temperatures slightly above the threshold for NO desorption. A similar behavior has also been observed in TPD studies conducted with Rh/Si02 (8). While the exact mechanism of dissociation is not established by these investigations, it seems plausible to propose that dissociation proceeds as indicated by reaction 2 in Fig. 11. 

An early suggestion (Bagotskii and Vesiliev, 1967) for a mechanism proposed an rds not as an electron transfer reaction but as a reaction on which some radical resulting from the dissociative adsorption of methanol reacted with OHads, the latter produced from the discharge of water. Then the rds was proposed as... 

When K[PtX(acac)2] (X = Cl, Br) is treated with a strong proton add the uncoordinated 0,0 site is protonated and complex (170) is formed.1606,1607 If the alkyl groups on the 0,0 -bonded acac ligand are non-equivalent, exchange can be observed. Although the mechanism has not been definitively proven, a dissociative mechanism is favored.160 This proposal correlates with the observations that the 0,0 -bonded chelate complex Pt(acac)2 will react with tertiary phosphines and nitrogen bases with substitution of one of the oxygen-bonded chelate arms.1609,1610 A variety of products are formed as outlined in Scheme 17. 

Kistiakowsky and Sternberg (64) have studied in 1953 the gas phase photobromination of ethylene and obtained results in general consistent with the earlier results of Schmitz and co-workers (92). They found the quantum yields of the photobromination to be independent of wavelength between 4800 and 6800 A., but observed no bromination at 7150 A., where insufficient energy was available for dissociation into two bromine atoms, although this radiation was absorbed by bromine. The mechanism proposed by Schmitz and co-workers... 

It was found that 5-nm-thick resist-mask polysilane films worked well in a direct lithography process on silicon substrates, resulting into a line width of 40 nm prepared by scanning probe microscope lithography, using a carbon nanotube tip.57 Thin PMPS films of 6—8 nm, with a molecular weight of 30,000 were prepared by spin casting and cured at 150°C to obtain a smooth surface. It has been interpreted that moisture was essential for the oxidation of the polysilane. The proposed mechanism involved dissociation of Si-Si bonds in polysilane by the electron injection from the carbon nanotube tip catalyzed by moisture. 

An alternative mechanism has been proposed,18 according to which the activated nitrogen dioxide molecule collides with a molecule of nitrogen pentoxide and causes dissociation of the latter. It is easier to decompose a molecule of nitrogen pentoxide than a molecule of nitrogen dioxide. The over-all reaction is exactly the same and one cannot distinguish between the two mechanisms by stoichiometry, but the facts just cited favor the mechanism proposed by Norrish and none of the experimental data are in opposition to it. 

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