Isomerization Of N-hexane Research Articles

Isomerization of paraffins under conditions of aromatization on an alumina-chromium-potassium oxide catalyst

1. 1. It was shown by a kinetic isotope method that during aromatization of n-hexane and n-hexenes on an alumina-chromium-potassium oxide catalyst at 530° isohexadienes are formed by skeletal isomerization of these hydrocarbons. Isomerization of n-hexane may also take place before dehydrogenation to olefin. 2. 2. It was found that rates of skeletal isomerization of n-hexane and n-hexenes under conditions of aromatization are much lower (by one order of magnitude and more) than corresponding rates of dehydrogenation. 3. 3. An assumption was put forward that skeletal isomerization of paraffins and olefins on an alumina-chromium-potassium oxide catalyst takes place by a sole mechanism via alkyl or alkylene intermediate surface forms with a positive charge.

Reactions of alkanes on supported Pt-Au alloys

Isomerization, dehydrocyclization and hydrogenolysis reactions of n-pentane and n-hexane were studied on supported Pt and Pt-Au alloys. The alloys studied were all in the composition range where this system is completely miscible (18% Pt in Au). Characteristic changes in selectivity towards the different reactions were observed when Pt was compared with alloys in the composition range 1–12.5% Pt and at temperatures 250–400 °C: (a) extremely diluted Pt in Au (1–4%) mainly catalyses isomerization; (b) alloys with a composition around 10% Pt favor dehydrocyclization; (c) pure Pt shows mainly isomerization. From the comparison of the n-pentane and n-hexane reactions it is possible to suggest a self-consistent picture of the mechanisms involved. For the alloys in (a) above the reaction mainly proceeds via a one-site isomerization mechanism. Catalysts in (b) are comparable to small particle catalysts and show cyclization and isomerization mainly via a cyclic mechanism. Pure Pt catalyses isomerization mainly via the bond shift mechanism (αα-γ adsorption) while ring closure probably proceeds via an αα-Ω adsorbed intermediate.

Isomerization of n-hexane on platinized Type Y zeolite binder-free bead catalyst

Isomerization of n-hexane on platinized Type Y zeolite binder-free bead catalyst

Dual-functional activities in nickel acid catalysts

The specific activity of supported nickel for benzene hydrogenation, ethane and n-hexane hydrogenolysis decreases with the increasing acidity of the support in the order of SiO 2 > Al 2O 3 > silica-alumina > Y faujasite; the Y faujasites (Na, Li, Ca, Mg) all have the same activities. The reducibility of 3% nickel faujasites decreases from 100% to zero in the order NaY ~ LiY > CaY > MgY > NH 4Y = 0. Specific n-hexane isomerization rates increase with acidity so that isomer yields are maximized for CaY. There are two types of sites on nickel. Site I (35%) promotes hydrogenolysis, Site II (65% weaker than Site I) hydrogenation-dehydrogenation. There is no evidence for synergistic influences between metal and acid sites.

Relation between catalytic properties and structure of metal films: II. Skeletal reactions of some C 6 alkanes

Skeletal isomerization, cyclization, and hydrogenolysis reactions of n-hexane and 2-methylpentane have been studied on various platinum and nickel film catalysts which were prepared under UHV conditions. The reactions were carried out in the presence of excess hydrogen in a static system at 273 °C, and conversions were restricted to <5%. The work particularly compared the catalytic behavior of ultrathin and thick films, where in the former the average metal density on the substrate was of the order of a monolayer. Nevertheless, these ultra-thin films actually consist of crystals <20 Å across, possibly together with monodispersed platinum atoms. The most detailed information was obtained from the reactions of n-hexane. On all nickel films hydrogenolysis (mainly to methane) was the dominant reaction, while on all platinum films the formation of C 6 isomerization and cyclization products was the more important. Nevertheless, with both metals the reaction over ultra-thin films had a much higher selectivity for the formation of C 6 products versus hydrogenolysis products than did the reaction over various thick films. Furthermore, ultrathin platinum films gave an increased proportion of cyclic C 6 products compared to thick films. The variation in catalytic selectivity, particularly with platinum, is interpreted on the following model: (1) the very small crystals of the ultra-thin films present an increased proportion of low-coordinated corner atoms, (ii) these corner atoms favor the formation of adsorbed carbocyclic reaction intermediates: these intermediates can lead to cyclic reaction products as well as providing a contributing path for isomerization, (iii) hydrogenolysis as well as isomerization by a CC bond shift mechanism are not favored by corner atoms, but require two or three adjacent platinum atoms on a crystal face; the triadsorbed intermediate which requires three platinum atoms is favored by a (111) face or facet, and itself favors isomerization by CC bond shift versus hydrogenolysis. Because the selectivities (versus hydrogenolysis) for isomerization by an adsorbed carbocyclic intermediate and by CC bond shift vary in different ways with the concentration of low coordinated corner platinum atoms, and because the relative importance of these two isomerization paths are influenced by hydrocarbon geometry, the overall dependence of selectivity on catalyst structure may, for a given hydrocarbon, be complex, and requires analysis in terms of the contributing mechanisms. Reactions with 2-methylpentane were so heavily in favor of the formation of methylcyclopentane that the dependence on films structure was not large. UHV ultra-thin films form a useful model system for studying the effects of particle size on catalyst selectivity without the complication due to possible surface contamination.

Effect of treatment conditions of Pd-zeolite catalysts on activity and selectivity in isomerization of n-hexane

Effect of treatment conditions of Pd-zeolite catalysts on activity and selectivity in isomerization of n-hexane

Structure and catalytic properties of nickel-zeolite catalysts

1. X-ray diffraction and magnetic investigations of Ni-zeolite catalysts, produced on the basis of type Y zeolites, indicated that in unreduced catalysts Ni2+ ions enter into the cavities of the zeolite, while in the case of reduction, the diffusion of Ni atoms to the outer surface leads to the appearance of large crystals of Ni. 2. The investigated catalysts are active in the isomerization of n-hexane and cyclohexane, as well as in the reaction of hydrogenation and hydroisomerization of benzene.

Paration of neohexane

A simple method was proposed for the preparation of neohexane by the isomerization of n-hexane under the influence of aluminum bromide, aluminum oxide and initiators.

Activation of an aluminoplatinum catalyst in the reactions of isomerization and hydrogenolysis of hydrocarbons by high-temperature treatment with hydrogen

1. The change in the activity of an aluminoplatinum catalyst (0.3% Pt) was investigated after its treatment (500–550°) with hydrogen, purified of oxygen and water, as well as with nitrogen (420°), containing ∼0.5% oxygen. 2. As a result of high-temperature treatment of the catalyst with hydrogen, the degree of isomerization of cyclohexane and n-hexane, as well as the hydrogenolysis of methylcyclopentane, very sharply increases. Treatment with nitrogen containing oxygen deactivates the catalyst in reactions of isomerization and hydrogenolysis of hydrocarbons and activates it in the hydrogenation of benzene. 3. Purification of the catalyst from oxygen and water by high-temperature treatment with hydrogen causes a change in the direction of hydrogenolysis of methylcyclopentane: although on a catalyst treated with hydrogen at 350–420° the five-membered ring of methylcyclopentane is cleaved primarily at the bonds far distant from the substituent, with the formation of isohexanes, after treatment of the catalyst with hydrogen at 550°, predominant cleavage of the five-membered ring occurs, at the bonds closestto the substituent,forming n-hexane.

The mechanisms of hydrogenolysis and isomerization of hydrocarbons on metals: II. Mechanisms of isomerization of hexanes on platinum catalysts

The isomerization of n-hexane (I), 2-methylpentane (II), and 3-methylpentane (III) were studied on various supported platinum catalysts, and the initial product distributions compared and identified with the initial distributions of the hydrogenolysis of methylcyclopentane. These results suggest that a common cyclopentane intermediate is involved in both reactions, adsorbed on the metal sites of the catalysts. The absence of 2,3-dimethylbutane in the product distributions, the simultaneous dehydrocyclization of (I), (II), and (III) to methylcyclopentane, and the difficulty of isomerizing the 2,3-dimethylbutane under the same conditions, are consistent with the proposed mechanism. On platinum films, another type of skeletal rearrangement also takes place: 2,3-dimethylbutane is formed from the hexanes, and benzene from methylcyclopentane. The mechanism probably involves a species adsorbed on two carbon atoms in the α,γ positions and is very similar in its effects to a carbonium ion mechanism. Only aromatization occurs when 1,1,3-trimethylcyclopentane reacts with hydrogen on a platinum film at 300°C, and that is a further proof of the possibility of ring enlargement on metal catalysts.

Isomerization, hydrogenation, and hydroisomerizatio n of certain hydrocarbons on synthetic zeolites of type y, containing metals of group VIII

1. The reactions of isomerization of n-hexane, cyclohexane, and the hydrogenation and hydroisomerization of benzene were investigated on synthetic CaY zeolites, containing Pt, Pd, Rh, and Ir. 2. On platinum and palladium catalysts (SiO2∶Al2O3=3.4), ∼60% isomeric hexanes can be obtained from hexane at 400° and 30 atm, and ∼50% methylcyclopentane can be obtained from cyclohexane at 370°. 3. Rhodium and iridium catalysts possess high hydrogenating activity. At 200° and 30 atm, the yields of cyclohexane were 97.8 and 91%, respectively. 4. With the hydroisomerization of benzene and the isomerization of cyclohexane as an example, it was demonstrated that the activity of the pd-catalyst is determined by the SiO2∶Al2O3 ratio in the zeolite. On Pd-zeolite, with SiO2∶Al2O3 ratio equal to 4.5, 67.3% methylcyclopentane can be obtained from benzene at 320° and 57.0% from cyclohexane at 330°.

Catalytic synthesis of neohexane

A laboratory method was proposed for the preparation of neohexane by the isomerization of n-hexane using technical aluminum chloride and some new initiators.

Isomerization of n-heptane and n-hexane on platinum, deposited on fluoborated aluminum oxide

1. n-Hexane and the n-pentane fraction isolated from the gasoline derived from Romashkin petroleum were isomerized on an aluminum-platinum catalyst that had been promoted with boron fluoride. 2. At 350° and a raw material space velocity of 2 h−1, n-hexane is converted to isohexanes to the extent of 64% and with a selectivity of 0.91. At 350° the isomerization of n-pentane to isopentane goes to the extent of 54% and with a selectivity of 0.94. 3. In the isomerization of the hexane the apparent activation energy was 19 kcal/mole.

Isomerization of alkanes in presence of AlCl3 under a pressure of hydrogen

1. It has been confirmed that by carrying out the isomerization of n-hexane in presence of AlCl3 under a high pressure of hydrogen cracking is reduced to a minimum and the formation of the so-called “lower layer” in the reaction products is completely avoided. 2. It has been established that increase in the hydrogen pressure reduces the rate of isomerization of n-hexane. 3. It has been established that the isomerization of n-hexane has a stepwise character; thus 2-methylpentane evidently forms an intermediate product in the formation of 2,2-dimethylbutane. 4. Some general suggestions have been made concerning the mechanism of the isomerization of n-hexane in presence of AlCl3 under a pressure of hydrogen.

Raman Spectroscopic Investigation of the Isomerization of n-Hexane

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRaman Spectroscopic Investigation of the Isomerization of n-HexaneSan-ichiro Mizushima, Hidetoshi Ohno, and Takehisa SakuraCite this: J. Am. Chem. Soc. 1950, 72, 10, 4820Publication Date (Print):October 1, 1950Publication History Published online1 May 2002Published inissue 1 October 1950https://doi.org/10.1021/ja01166a517RIGHTS & PERMISSIONSArticle Views61Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (153 KB) Get e-Alerts Get e-Alerts

Investigation of the Isomerization of n-Hexane by Means of the Raman Effect

Investigation of the Isomerization of n-Hexane by Means of the Raman Effect