- Impact of the Spatial Organization of Bifunctional Metal–Zeolite Catalysts on the Hydroisomerization of Light Alkanes
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Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one-dimensional zeolites (ZSM-22 and mordenite) and a γ-alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n-heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the ??intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low-molecular-weight reactants.
- Cheng, Kang,Harmel, Justine,Oenema, Jogchum,Sunley, Glenn,Yoshida, Hideto,Ze?evi?, Jovana,Zhang, Zhaorong,de Jong, Krijn P.,van der Wal, Lars I.
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supporting information
p. 3592 - 3600
(2020/02/05)
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- Influence of chlorine on the catalytic properties of supported rhodium, iridium and platinum in ring opening of naphthenes
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Pt, Ir and Rh were deposited on SiO2 or Al2O 3 using chlorinated precursors and various amounts of HCl in the impregnation medium. The Br?nsted and Lewis acidities increased with the chlorine content of the alumina supported catalysts. The silica-supported catalysts only presented Lewis acid sites. The catalysts were evaluated in methylcyclopentane (MCP) and methylcyclohexane (MCH) ring-opening (RO) under pressure (2.85 and 3.95 MPa, respectively), from 200 to 425 C. For MCP conversion, the acidity of the alumina support had no sensitive effect on the activity and selectivity to RO products, and few effects on the distribution of RO products. No isomerization or hydrocracking products were observed, confirming that these reactions occurred mainly on the metal function, which was not modified by the presence of chlorine. The nature of the support, SiO 2 or Al2O3, had a strong effect on both the activity (1.9 against 0.5 mol h-1 g-1metal for Ir/Al2O3 and Ir/SiO2, respectively at 225 C) and selectivity to RO products (99.6% against 97.5% for Ir/Al2O 3 and Ir/SiO2, respectively, at 80% of MCP conversion) for Ir catalysts only. Interestingly, the Rh/SiO2 exhibited a high selectivity for converting MCP to RO products, similar to Ir/Al 2O3, i.e. 99.6% at 80% of conversion. Depending on the metal and the supports, three types of behavior were observed for MCH ring-opening: (i) a direct ring-opening on the metal function whatever the support for Ir, (ii) a first step of isomerization, and then a need of a sufficiently acidic support, for Pt and (iii) an intermediate behavior for Rh, which was able to either directly convert MCH in absence of acidic support or favor a bifunctional mechanism on chlorinated alumina.
- Samoila,Epron,Marécot,Especel
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p. 207 - 219
(2013/07/26)
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- Hydrocarbon separation
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Process for the separation of close boiling compounds comprising distilling a hydrocarbon mixture of said compounds in the presence of a high boiling diluent liquid and a solid adsorbent. The high boiling diluent is withdrawn from the bottom of the distillation column and recycled to the column. The process is particularly suitable for the separation of straight-chain isomers from isomerate mixtures, the separation of benzene from hydrocarbon mixtures and the separation of paraffins from olefins.
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Page/Page column 11
(2008/12/06)
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- Isomerization of N-heptane in naphtha cuts
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A process for the isomerization of normal heptane contained within a naphtha stream, such as a C6-C8 naphtha, in which the naphtha stream is fractionated into a fraction substantially free of normal heptane and a fraction containing normal heptane. The fraction containing normal heptane is contacted with an isomerization catalyst in an isomerization zone operated as a singe pass fixed bed reactor having a single effluent to isomerize a portion of said normal heptane to branched heptane. The effluent is recovered from said isomerization zone and the effluent is fractionated to recover said branched heptane. The unconverted normal heptane is recovered and returned to the isomerization since it can be separated from the branded heptanes by fractionation.
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Page/Page column 4
(2008/06/13)
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- METHOD FOR THE PRODUCTION OF NON-AROMATIC HYDROCARBONS
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The invention relates to a method for the production of long-chain, branched-chain and/or cyclic hydrocarbons. A low molecular weight alkyl halide and a fused salt are firstly prepared. The fused salt contains an electrophilic compound and a reducing agent and is free from oxygen and oxygen compounds. The alkyl halide is then brought into contact with the fused salt such that long-chain, branched-chain and/or cyclic hydrocarbons are formed in the fused salt. The hydrocarbons formed in the fused salt are drawn off and can subsequently be separated from unreacted starting materials. By means of the above method, hydrogen can be produced during the reaction of the low molecular weight alkyl halide. The risk of oxidation of the alkane produced to give carbon monoxide or carbon dioxide is avoided by means of the reducing conditions in the fused salt. The product distribution can be controlled by means of suitable selection of the composition of the fused salt. Highly-branched hydrocarbons are produced with the preferred application of a sodium chloroaluminate fused salt.
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- Process of paraffin hydrocarbon isomerisation catalysed by an ionic liquid in the presence of a cyclic hydrocarbon addditive
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A process for the conversion of linear and/or branched paraffins hydrocarbons, catalysed by an ionic liquid catalyst, in the presence of a cyclic hydrocarbon additive containing a tertiary carbon atom. The presence of the specific hydrocarbon additives influences the reaction mechanism by increasing the selectivity towards the formation of paraffin hydrocarbons with a higher degree of branching.
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- C7+ paraffin isomerisation process and catalyst therefore
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There is provided a process for selective isomerisation of C4+ paraffins using a catalyst comprising mixed aluminium, tungsten and zirconium oxides, and a hydrogenation/dehydrogenation component, such as palladium or other Group VIII metals. The feed may optionally also include shorter paraffins, aromatics or cycloparaffins.
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- Catalyst and process for contacting a hydrocarbon and ethylene
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A process of contacting at least one feed hydrocarbon, containing three to about seven carbon atoms per molecule, and ethylene in a hydrocarbon-containing fluid in the presence of a catalyst composition to provide at least one product hydrocarbon isomer containing about four to about nine carbon atoms per molecule is provided. The at least one feed hydrocarbon can be selected from paraffins, isoparaffins, and the like and combinations thereof. The catalyst composition contains a hydrogen halide component, a sulfone component, and a metal halide component.
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- Disproportionation of hydrocarbons
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A novel hydrocarbon disproportionation process is provided and includes contacting a hydrocarbon feed comprising at least one paraffin with a disproportionation catalyst comprising a support component, a metal, and a halogen in a disproportionation reaction zone under disproportionation reaction conditions.
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- Gas to liquid conversion process
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A process is disclosed for the conversion of lower molecular weight hydrocarbons, such as methane, into higher molecular weight hydrocarbon products, such as hydrocarbons having between 4 and 29 carbons. The process includes forming hydrated electrons, such as by mixing the lower molecular weight hydrocarbons with water and contacting the mixture with an energy source to form hydrated electrons. The hydrated electrons react with the methane to form hydrogen and higher molecular weight hydrocarbon products. Also disclosed is a related process for converting higher molecular weight hydrocarbons to lower molecular weight hydrocarbons by forming a mixture of higher molecular weight hydrocarbons and water and contacting the mixture with an energy source to form hydrated electrons that react with the higher molecular weight hydrocarbons to form hydrogen and lower molecular weight hydrocarbon products.
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Page column 7
(2008/06/13)
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- Selectively Weakened C-C ?-Bond in Cation Radicals of Linear and Branched Pentanes As Studied By Electron Spin Resonance
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Radical cations which have the fully extended structure (trans-trans conformation) but have lost the symmetry of the mother molecules were detected by electron spin resonance for n-pentane, 3-methylpentane, and 3,3-dimethylpentane in frozen matrices at 4 K.It was indicated, with the aid of an INDO calculation, that one of the two inner C-C bonds in the main chain is elongated and the unpaired electron tends to be confined in this bond.Selective bond elongation was also shown for the trans-gauche conformers of 3-methylpentane and 3,3-dimethylpentane cations.These facts suggest that selective elongation of a C-C bond is essential with alkane cations even if it is not Jahn-Teller active.This selective weakening of a skeletal bond should be related to the selectivity in the bond scission in alkane radiolysis.In addition, hole migration between the solute alkanes in the frozen matrices at 77 K was suggested from the radical conversion between the different conformers.
- Toriyama, Kazumi,Okazaki, Masaharu
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p. 6986 - 6991
(2007/10/02)
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- IONIC METHYLATION OF DICHLORO- AND DIBROMOALKANES
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The dichloro and dibromo derivatives of hydrocarbons are methylated by the action of tetramethylsilane in the presence of aluminum bromide with the formation of hydrocarbons containing a quaternary carbon atom irrespective of whether the halogen atoms are at one or at different carbon atoms.
- Parnes, Z. N.,Romanova, V. S.,Vol'pin, M. E.
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p. 258 - 260
(2007/10/02)
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- Reactions of tert-Butyllithium with α,ω-Dihaloalkanes. Evidence for Single-Electron-Transfer-Mediated Metal-Halogen Interchange Involving Alkyl Radical-Halide Ion Adducts
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The reactions of tert-butyllithium (t-BuLi) with primary α-iodo-ω-haloalkanes and α,ω-dibromoalkanes have been investigated in experiments conducted at -23 deg C in n-pentane-diethyl ether (3:2 by volume) solution.It has been found that production of an α-lithio-ω-haloalkane (1) by metal-halogen interchange at one end of a 1,3-, 1,4-, or 1,5-dihalide results in intramolecular coupling to give cycloalkanes in high yield.As the chain length of the dihalide is increased beyond five carbon atoms the production of an α,ω-dilithio species by interchange at bothends of the dihalide ceases to be excluded by cyclization of 1 and a precipitous drop in the yield of cycloalkane was found to occur in reactions of 1,6-diiodoalkanes with t-BuLi.Metal-halogen interchange was the exclusive process observed in reactions of α,ω-dihalides with t-BuLi provided at least one halogen of the substrate was an iodine.By contrast, similar treatment of α,ω-dibromoalkane provided only minor amounts of product attributable to metal-halogen interchange.Under conditions that provide an essentially quantitative yield of carboxylic product from reductive cyclization of 1 generated from 1,5-diiodo-3,3-dimethylpentane, the corresponding 1,5-dibromide was converted to a mixture composed of cycloalkane, products from Wurtz-type coupling with t-BuLi, and quantities of parent alkane from formal reduction of the dihalide.The mechanism of the metal-halogen interchange was further probed by using 6-halo-1-hexene substrates.Observation of cyclized product from the reaction of t-BuLi with 6-bromo- and 6-iodo-1-hexene demonstrated that the interchange between t-BuLi and primary alkyl bromides and iodides occurs predominantly via single-electron-tranfer (SET) process.Incorporation of alkyl radical-halide ion adducts with halogen dependent lifetimes as intermediates following SET from alkyllithium to alkyl halide serves to explain the disparate behavior of alkyl bromides and iodides when treated with t-BuLi.A unifield SET-mediated mechanism for metal-halogen interchange and Wurtz coupling is presented.
- Bailey, William F.,Gagnier, Paul R.,Patricia, Jeffrey J.
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p. 2098 - 2107
(2007/10/02)
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- Photophysical and Photochemical Behaviour of Tetrahydridobis(bis(1,2-diphenylphosphino)ethane)molybdenum and -tungsten: Optical Emission and Photoreduction of Alkenes
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The complexes H4M(DPPE)2 and D4M(DPPE)2 (M = Mo, W; DPPE = bis(1,2-diphenylphosphino)ethane) exhibit emission of visible light upon photoexcitation at 77 K in 2-methyltetrahydrofuran.The emission lifetime at 77 K for the W species (ca.13 μs) is shorter than for the Mo species (ca.90 μs) and is independent of whether the substance is the 1H or 2H species.The shorter lifetime for the W species is consistent with an emissive triplet state that is antibonding with respect to M-H2 interactions, since the solution photochemistry at 298 K is dominanted by H2 loss.While the lifetime of the 1H and 2H species is the same, the quantum yield of emission for M = Mo is higher for the 2H species (0.28) than for the 1H species (0.21).The data are consistent with an effect from 2H that diminished nonradiative decay from the singlet excitet state reached by direct absorption.This diminished nonradiative decay allows intersystem crossing to be more competitive, yielding the emissive triplet with higher efficiency.Irradiation of the H4M(DPPE)2 species in the presence of an alkene (e.g., 1-pentene, cis-2-pentene, 3,3-dimethyl-1-pentene, cyclopentene) results in stoichiometric reduction to form an alkane; i.e., each H4M(DPPE)2 molecule yields two molecules of alkane.Irradiation of H4M(DPPE)2 in the presence of alkene and 10 psi of H2 yielsd photoassisted alkane formation, yielding many alkane molecules per H4M(DPPE)2 initially present, as illistrated with the reduction of 1-pentene.The intriguing finding concerning the photoreduction of 1-pentene or cis-2-pentene is that the reduction occurs without detectable isomerization to cis- and trans-2-pentene or 1- and trans-2-pentene, respectively, an unprecedented results for such photoassisted alkene reduction using polyhydride precursors.
- Graff, James L.,Sobieralsky, Ted J.,Wrighton, Mark S.,Geoffroy, Gregory L.
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p. 7526 - 7533
(2007/10/02)
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- REACTION OF α,ο-DIIODIDES WITH t-BUTYLLITHIUM: FACILE ROUTE TO THREE-, FOUR- AND FIVE-MEMBERED CYCLOALKANES
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Carbocyclic three-, four- and five-membered rings are formed in good to excellent yield (87-100percent) upon treatment of the appropriate α,ο-diiodide with t-butyllithium in pentane-ether solution at -23 deg C.The corresponding dibromides do not undergo clean cyclization.
- Bailey, William F.,Gagnier, R. Paul
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p. 5123 - 5126
(2007/10/02)
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- Hydrogenolysis of Alkanes with Quaternary Carbon Atoms over Pt and Ni Black Catalysts
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Hydrogenolysis of hydrocarbons with quaternary C atoms (neopentane, neohexane, 2,2,3-trimethylbutane, 2,2- and 3,3-dimethylpentanes and 2,2,3,3-tetramethylbutane) has been studied over Pt and Ni black catalysts.The reactivities of different types of C-C bond have been determined.The probability of C-C bond rupture where one of the carbon atoms is quaternary is inversely proportional to the bond dissociation energy.On Pt, two essential types of hydrogenolysis can be distinguished.One reaction is responsible for the breaking of internal C-C bonds attached to the quaternary carbon atom and the other for demethylation.With larger molecules, the former reaction is preferred and the surface intermediate should be 1,4-diadsorbed, while that for the latter reaction is 1,3-diadsorbed.Nickel, as previously suggested, causes terminal C-C rupture, although with branched hydrocarbon reactants internal C-C bond rupture is also possible, presumably via 1,4-adsorption.
- Zimmer, Helga,Tetenyi, Pal,Paal, Zoltan
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p. 3573 - 3586
(2007/10/02)
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- CYCLIZATION OF C7-ALKANES OVER Pt BLACK CATALYST
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C6-and C5-cyclization of heptane isomers (and also, olefin formation as a related process) over Pt-black have been studied in pulse and circulation systems.Hydrogendeficient conditions favour aromatization, via presumably terminal olefins.C5-Cyclization in the presence of more hydrogen is accompanied by internal olefin formation.Relative reactivities of all heptane isomers have been measured; this shows that cyclization is easier between terminal methyl groups.Optimum hydrogen pressures for both types of cyclization have been determined (and compared with hydrogenolysis, too).Earlier mechanism suggestion for aromatization and cyclopentane formation have been confirmed; the distinction between two types of bond shift mechanisms producing aromatics (from substituted pentanes) and saturated isomers, respectively, has recieved additional support facilitating the identification of these two reactions with mechanisms proposed in the literature.
- Zimmer, H.,Paal, Z.,Tetenyi, P.
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p. 513 - 532
(2007/10/02)
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