Adsorbed carbocations as transition states in heterogeneous acid catalyzed transformations of hydrocarbons

Kazansky, V.B.

doi:10.1016/s0920-5861(99)00031-0

Cited by 173 publications

(121 citation statements)

References 26 publications

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“…Recently, Kazansky showed that neither the adsorbed carbeni- um ions nor the adsorbed carbonium ions could be considered as free species because they are strongly electrostatically bonded to the surface of solid acids. [16] We choose propylene as a typical component of the gaseous fraction and 1-dodecene as a typical component of the liquid fraction of the degradation products of PP to investigate effects of composition and combined states of the catalysts on the yield of MWNTs (Table 2). Interestingly, the same phenomena was displayed for both 1-hexene and 1-dodecene, but the yield of MWNTs obtained from propylene was almost the same for the three different catalyst mixtures.…”

mentioning

confidence: 99%

The Combined Catalytic Action of Solid Acids with Nickel for the Transformation of Polypropylene into Carbon Nanotubes by Pyrolysis

Song

Jiang

et al. 2007

Chemistry A European J

105

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The effects of both organically modified montmorillonite (OMMT) and Ni(2)O(3) on the carbonization of polypropylene (PP) during pyrolysis were investigated. The results from TEM and Raman spectroscopy showed that the carbonized products of PP were mainly multiwalled carbon nanotubes (MWNTs). Surprisingly, a combination of OMMT and Ni(2)O(3) led to high-yield formation of MWNTs. X-ray powder diffraction (XRD) and GC-MS were used to investigate the mechanism of this combination for the high-yield formation of MWNTs from PP. Brønsted acid sites were created in degraded OMMT layers by thermal decomposition of the modifiers. The resultant carbenium ions play an important role in the carbonization of PP and the formation of MWNTs. The degradation of PP was induced by the presence of carbenium ions to form predominantly products with lower carbon numbers that could be easily catalyzed by the nickel catalyst for the growth of MWNTs. Furthermore, carbenium ions are active intermediates that promote the growth of MWNTs from the degradation products with higher carbon numbers through hydride-transfer reactions. The XRD measurements showed that Ni(2)O(3) was reduced into metallic nickel (Ni) in situ to afford the active sites for the growth of MWNTs.

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mentioning

confidence: 99%

The Combined Catalytic Action of Solid Acids with Nickel for the Transformation of Polypropylene into Carbon Nanotubes by Pyrolysis

Song

Jiang

et al. 2007

Chemistry A European J

105

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“…A value like this is certainly smaller (in absolute numbers) than the value that would be expected if the adsorption corresponded to the protonation of an olefin (-71 KJ/mol in HBeta zeolite, Si/Al = 16 [65]). Then, if the bifunctional mechanism proposed for the isomerization of n-octane is accepted, this result would indicate that the olefin is not protonated, i.e., not a real surface carbenium ion is formed, but only partial charge transfer occurs, as has been proposed by Boronat [62] and Kazansky [66].…”

Section: Kinetics For the Isomerization Of N-octane To Methylheptanesmentioning

confidence: 76%

Comparison of Large Pore Zeolites for n‐Octane Hydroisomerization: Activity, Selectivity and Kinetic Features

Chica¹,

Corma²

2007

Chemie Ingenieur Technik

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Dedicated to Professor Dr.-Ing. J. Weitkamp on the occasion of his 65th birthdayThe hydroisomerization of n-octane has been catalyzed by different zeolitic structures with large pore size (12 MR). It has been seen that channel topology, chemical composition, crystal size, and adsorption properties are of paramount importance for improving the isomerization activity and selectivity. Nanocrystalline beta zeolite (30 nm) with large pore size (0.66 × 0.67 and 0.56 × 0.56 nm), and high aluminum content (Si/Al = 16), was the best catalyst to produce multibranched isomers. Cracking reactions also occur together with isomerization and the product distribution will depend on the rate constant and relative activation energies of isomerization, desorption, and cracking. Furthermore, a complete kinetic study of n-octane isomerization has been carried out with beta zeolite, and kinetic rate constants, heats of adsorption, and activation energies have been determined for each individual isomerization step. The rate of isomerization of n-octane to monobranched products was found to be faster than the rate of cracking of dibranched products and the rate of isomerization of mono-to dibranched products. It should be possible to obtain high yields of dibranched alkanes by distillation and recycling units, or by using membrane reactors.

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“…Indeed, it was proposed that surface alkoxides are in fact the most energy favored species to serve as stable reaction intermediates (Kazansky et al, 1996;Rigby et al, 1997;Kazansky, 1999;Natal-Santiago et al, 1999). In this view, a covalent carbonyl bond is responsible for binding the alkoxide to the catalytic surface.…”

Section: Stability Considerations Concerning Carbenium Ionsmentioning

confidence: 99%

“…Hence, the nature of this resulting carbenium ion-like transition state will determine the effective energy barrier for the reaction, and therefore, its relative reactivity. Their similarity with the carbenium ion intermediates during hydrocarbon transformations in solution constitutes the basis for describing the chemistry of surface alkoxides by means of surfacebonded carbenium ions acting as reaction intermediates (Kazansky, 1999). The two approaches become equivalent after the introduction of the concept of stabilization energy, a concept that accounts for the energy differences between gas phase carbenium ions and their corresponding covalently surface-bonded alkoxy intermediates (Martens et al, 2000;Thybaut et al, 2001).…”

Section: Stability Considerations Concerning Carbenium Ionsmentioning

confidence: 99%

Kinetic Modeling using the Single-Event Methodology: Application to the Isomerization of Light Paraffins

Surla

Denis

Verstraete

et al. 2011

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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Résumé -Modélisation cinétique basée sur la méthodologie des événements constitutifs : application à l'isomérisation des paraffines légères -L'établissement de modèles cinétiques est une étape importante du développement de procédés de raffinage. En effet, ces modèles peuvent être utilisés pour prédire les performances du procédé, pour optimiser l'opération de l'unité et pour concevoir de façon optimale le réacteur et le procédé associé (choix du réacteur, détermination des conditions de marche optimale, utilisation de recyclages, etc.). La demande actuelle de modèles se focalise particulièrement sur la mise au point de modèles détaillés et prédictifs, qui sont capables de prendre en compte des variations importantes dans la conduite du procédé. De ce fait, ils doivent être extrapolables à des conditions opératoires très différentes ou à des charges très diverses. La modélisation cinétique par événements constitutifs satisfait ces critères car elle permet d'obtenir une prédiction détaillée des effluents des réacteurs. La théorie des événements constitutifs a été initialement développée pour la chimie radicalaire [Clymans et Froment (1984) Comput. Chem. Eng. 8, 2, 137-142 ; Hillewaert et al. (1988) AIChE J. 34, 1, 17-24 ;Willems et Froment (1988a) Ind. Eng. Chem. Res. 27, 11, 1959-1966Willems et Froment (1988b) Ind. Eng. Chem. Res. 27, 11, 1966-1971 16,[5879][5880][5881][5882][5883][5884][5885][5886][5887][5888][5889][5890][5891]. Cette méthodologie développée au "Laboratorium voor Petrochemische Techniek" à l'Université de Gand consiste à construire un réseau réactionnel exhaustif mais décrit par un nombre limité de paramètres cinétiques indépendants. Le comportement de charges complexes peut alors être prédit sur la base d'études effectuées sur des molécules modèles. Cette méthodologie est appliquée par IFP Energies nouvelles à plusieurs procédés de raffinage. L'objet de cet article est de décrire cette méthodologie de façon détaillée et de présenter son application à l'isomérisation des paraffines C5-C6.Abstract -Kinetic Modeling using the Single-Event Methodology: Application to the Isomerization of Light Paraffins -The construction of kinetic models is an important step in the development of refining processes. Indeed, these models can be used to predict the performances of the process, to optimize the operation of a unit and to optimally design a reactor and the associated process (choice of the reactor configuration, determination of optimal operating conditions, use of recycles, etc.). The current demand for models is particularly focused towards the development of detailed predictive models that are able to

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Adsorbed carbocations as transition states in heterogeneous acid catalyzed transformations of hydrocarbons

Cited by 173 publications

References 26 publications

The Combined Catalytic Action of Solid Acids with Nickel for the Transformation of Polypropylene into Carbon Nanotubes by Pyrolysis

The Combined Catalytic Action of Solid Acids with Nickel for the Transformation of Polypropylene into Carbon Nanotubes by Pyrolysis

Comparison of Large Pore Zeolites for n‐Octane Hydroisomerization: Activity, Selectivity and Kinetic Features

Kinetic Modeling using the Single-Event Methodology: Application to the Isomerization of Light Paraffins

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