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Surface cyclopentanes

Fig. 12.4. Vapor-to-water transfer data for saturated hydrocarbons as a function of accessible surface area, from [131]. Standard states are 1M ideal gas and solution phases. Linear alkanes (small dots) are labeled by the number of carbons. Cyclic compounds (large dots) are a = cyclooctane, b = cycloheptane, c = cyclopentane, d = cyclohexane, e = methylcyclopentane, f = methylcyclohexane, g = cA-l,2-dimethylcyclohexane. Branched compounds (circles) are h = isobutane, i = neopentane, j = isopentane, k = neohexane, 1 = isohexane, m = 3-methylpentane, n = 2,4-dimethylpentane, o = isooctane, p = 2,2,5-tri-metbylhexane. Adapted with permission from [74], Copyright 1994, American Chemical Society... Fig. 12.4. Vapor-to-water transfer data for saturated hydrocarbons as a function of accessible surface area, from [131]. Standard states are 1M ideal gas and solution phases. Linear alkanes (small dots) are labeled by the number of carbons. Cyclic compounds (large dots) are a = cyclooctane, b = cycloheptane, c = cyclopentane, d = cyclohexane, e = methylcyclopentane, f = methylcyclohexane, g = cA-l,2-dimethylcyclohexane. Branched compounds (circles) are h = isobutane, i = neopentane, j = isopentane, k = neohexane, 1 = isohexane, m = 3-methylpentane, n = 2,4-dimethylpentane, o = isooctane, p = 2,2,5-tri-metbylhexane. Adapted with permission from [74], Copyright 1994, American Chemical Society...
Experimental support for the suggestion that depleted surface layers result in attractive forces (at T 0) has come from recent experiments (J.K. and Y.A., submitted) where mica surfaces partially covered by polystyrene in cyclopentane above the 0-temper-ature show a clear mutual attraction, which disappears when full surface coverage by the polymer is attained. [Pg.236]

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... [Pg.302]

C5 Cyclization of various alkanes 38, 38a) over platinum on carbon was first observed in 1954. Barron et al. 15a) postulated the formation of a surface C5 cyclic intermediate, which may desorb as a cyclopentanic hydrocarbon or may produce skeletal isomers without desorption. [Pg.292]

SiO)2Ta Cp[ activates, at room temperature, the C-H bonds of cyclic alkanes (from cyclopentane to cyclooctane) to form the corresponding surface tantalum-cycloalkyl stoichiometrically with evolution of hydrogen (Scheme 3.2) [20] ... [Pg.81]

Davis and Somorjai collected and evaluated kinetic data from more than 150 papers on the HC reactions (181) and their survey shows more of such differences (see cyclopentane versus pentane on Rh) which are not easy to rationalize. However, when one considers what has been said above [effects (l)-(4) of "carbon layers], the following hypothesis emerges The differences among the data of different authors are due to the differences in the structure of the "carbon layer on their metal surface. This idea is supported by the following information. [Pg.184]

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... [Pg.88]

The low-temperature VEEL spectra of the species on Ru(0001) at 170 K and on Pt(lll) at 90 K are similar in contour and show broad and strong soft-mode absorptions at ca. 2610 and 2690 cm 1, respectively. The strengths of these features imply that the median plane of the flexible C5 skeleton is approximately parallel to the metal surface so that multiple C-H - M contacts are once again possible. The RAIR investigation at ca. 140 K of cyclopentane on Pt(lll) gives high resolution and shows the soft-mode absorption to be very broad. The positions of the nonagostic r>CH absorptions and of the VEELS features at wavenumbers less than 1500 cm 1 are as expected for the intact, nondissociatively adsorbed species (257, 259). [Pg.236]

In each case, as the temperature was raised to 200 K, a markedly changed VEEL spectrum was observed, which was attributed to the formation of cyclopentene by dehydrogenation (see Section VI.B). Avery s study of the adsorption of cyclopentane was continued to 260 K, whereby a much simpler spectrum was obtained, convincingly attributed to the formation of the 175-C5H5 (i75-cyclopentadienyl) structure adsorbed flat on the surface. The 200 K spectrum of the species on Ru(0001) may even contain some features characteristic of this species (strong bands at 758 and 3057 cm 1). [Pg.236]

Skeletal rearrangement reactions over Pt single crystals have been studied for methyl cyclopentane, 2- and 3-methylpentane350 and for n-hexane.3sl One conclusion351 is that whereas aromatization reactions are very sensitive to surface structure [Pt(l 11)> Pt(100)], isomerization, Cs-cyclization, and hydrogenolysis reactions display little dependence on structure. Temperature and H2 pressure are more important in affecting the selectivity. [Pg.193]


See other pages where Surface cyclopentanes is mentioned: [Pg.39]    [Pg.39]    [Pg.133]    [Pg.174]    [Pg.370]    [Pg.280]    [Pg.41]    [Pg.192]    [Pg.57]    [Pg.58]    [Pg.223]    [Pg.283]    [Pg.176]    [Pg.188]    [Pg.303]    [Pg.322]    [Pg.178]    [Pg.954]    [Pg.197]    [Pg.105]    [Pg.237]    [Pg.242]    [Pg.242]    [Pg.244]    [Pg.225]    [Pg.59]    [Pg.63]    [Pg.28]    [Pg.35]    [Pg.201]    [Pg.158]    [Pg.160]    [Pg.160]    [Pg.195]    [Pg.41]    [Pg.192]    [Pg.544]    [Pg.107]   
See also in sourсe #XX -- [ Pg.39 ]




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