Reactions of n-alkanes over H-ZSM-5: Detection of reactive intermediates

Dass, D.V.; Odell, A. L.

doi:10.1016/0021-9517(88)90254-0

Cited by 24 publications

(6 citation statements)

References 6 publications

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“…Duringt he cyclization process, other reactions such as alkenes cracking, olefin dimerizationo ro ligomerization and aromatics alkylation may simultaneously occur.T his prevents acquiring experimental evidencef or clarifyingi fa lkene dehydrogenationo ccurs prior to cyclization or not. [24,25] Thus, some researchersm ade at ry to investigate dienesc yclization mechanism on H-ZSM-5 by calculating 1,5-and 1,6-cyclization pathways using embedded cluster. [26,27] It has been found that cyclization of dienes generated from alkenesd ehydrogenation is practicable.…”

Section: Introductionmentioning

confidence: 99%

Reaction Mechanism for Direct Cyclization of Linear C₅, C₆, and C₇ Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

Chen

Wei

et al. 2018

ChemPhysChem

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Although dienes or trienes have been shown to be possible precursors for cyclization, direct cyclization of alkenes or alkoxides has not been systematically studied yet. Thus, the reaction mechanism of cyclization of linear alkenes over H-ITQ-13 was investigated here by density functional theory considering dispersive interactions (DFT-D). The similar free energy of different linear alkoxides of the same carbon number suggests that they can co-exist in the H-ITQ-13 intersection at 673.15 K during the methanol to olefins (MTO) process. The formation of linear alkenes by olefins methylation with methoxyl groups (ZOCH ), trimethyloxonium ions (TMO ), and methanol are kinetically more favorable than by dimerization of olefins. Linear alkoxides or alkenes prefer direct cyclization to cycloalkanes rather than hydride transfer to diene. This study provides new insight into the alkene cyclization and aromatization mechanisms in MTO process.

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Section: Introductionmentioning

confidence: 99%

Reaction Mechanism for Direct Cyclization of Linear C₅, C₆, and C₇ Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

Chen

Wei

et al. 2018

ChemPhysChem

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“…As a consequence, over the last 50 years there has been a considerable drive to develop economically viable aromatization routes in industry. − However, aromatization catalysts suffer from a number of deficiencies. Monofunctional acid catalysts exhibit relatively low aromatics yields which is due to preferentially high cracking, isomerization, and β-scission reactivity. − Bifunctional metal/H-ZSM-5 catalysts using Ga, − Zn, − and Pt ,,− dramatically improve aromatics yields but are prone to deactivation via coking 31 and, although better than purely acidic catalysts, are nevertheless limited in both aromatics yield and selectivity toward H 2 versus CH 4 byproducts.…”

Section: Introductionmentioning

confidence: 99%

DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

2003

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We conducted density functional theory calculations to identify the complete cyclization mechanism (ring formation and ring expansion) for protonated hexadiene in the gas-phase as a precursory means of studying aromatization of light alkanes in acidic zeolite catalysts. We identify the rate-determining step to consist of ring expansion from a methylcyclopenta carbenium precursor to a stable cyclohexa carbenium intermediate, exhibiting an activation barrier of 9.6 kcal/mol and proceeding through a bicyclic intermediate starting from a secondary cyclopentyl carbocation. This pathway for ring closure was preferred over tertiary precursor expansion and direct cyclization to a cyclohexyl carbocation. Expecting carbocation intermediates to be represented by alkoxide species near Brønsted acid sites, we calculated the relative stability of primary, secondary, and tertiary alkoxide analogues to cyclopentyl carbocation intermediates involved in ring expansion and notice a reversal of stability relative to gas-phase carbocation stabilities (i.e., primary > secondary > tertiary stability). However, on the basis of the notion that transition state stability depends heavily on carbocation character of the transition state, even in alkoxide-based chemistry, we conclude that ring expansion would nevertheless constitute the rate-determining step in a zeolite-catalyzed mechanism.

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“…The catalytic transformations of light hydrocarbons (Cz-Cs) to aromatics have been studied intensively for the last two decades [1][2][3][4].The reason for such a high interest in this reaction is that the aromatics produced can be utilized as feedstock for the petrochemical industry for producing chemicals. Ga-ZSM-5, Zn-ZSM-5 and Pt-ZSM-5 catalysts have received much attention for the 0133-1736/97/US$12.00.…”

Section: Introductionmentioning

confidence: 99%

Aromatization ofn-butane over Ni-ZSM-5 and Cu-ZSM-5 zeolite catalysts prepared by using Ni and Cu impregnated silica, fiber

Kumar

Byggningsbacka

Lindfors

1997

React Kinet Catal Lett

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The reaction of n-butane aromatization was carried out over Ni-ZSM-5 and Cu-ZSM-5 zeolite catalysts prepared by using Ni and Cu impregnated silica fiber during the process of ZSM-5 zeolite synthesis. The catalysts prepared were characterized by X-ray powder diffraction, nitrogen adsorption and X-ray fluorescency. "The acidic properties of the catalysts were investigated by temperature-programmed desorption of ammonia using a mass spectrometer equipped with a QTMD detector. The effect of catalyst pretreatment, reaction temperature, and time on stream on the reaction of n-butane to aromatic hydrocarbons were investigated. The modification of ZSM-5 by Ni and Cu increased the selectivity to aromatic hydrocarbons. The state of Ni and Cu and theft stabilization ill the ZSM-5 structure was highly influenced by the mode of catalyst pretreatments.

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Reactions of n-alkanes over H-ZSM-5: Detection of reactive intermediates

Cited by 24 publications

References 6 publications

Reaction Mechanism for Direct Cyclization of Linear C₅, C₆, and C₇ Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

Reaction Mechanism for Direct Cyclization of Linear C₅, C₆, and C₇ Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

Aromatization ofn-butane over Ni-ZSM-5 and Cu-ZSM-5 zeolite catalysts prepared by using Ni and Cu impregnated silica, fiber

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Reactions of n-alkanes over H-ZSM-5: Detection of reactive intermediates

Cited by 24 publications

References 6 publications

Reaction Mechanism for Direct Cyclization of Linear C5, C6, and C7 Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

Reaction Mechanism for Direct Cyclization of Linear C5, C6, and C7 Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

DFT-Based Reaction Pathway Analysis of Hexadiene Cyclization via Carbenium Ion Intermediates: Mechanistic Study of Light Alkane Aromatization Catalysis

Aromatization ofn-butane over Ni-ZSM-5 and Cu-ZSM-5 zeolite catalysts prepared by using Ni and Cu impregnated silica, fiber

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Reaction Mechanism for Direct Cyclization of Linear C₅, C₆, and C₇ Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory

Reaction Mechanism for Direct Cyclization of Linear C₅, C₆, and C₇ Alkenes over H‐ITQ‐13 Zeolite Investigated Using Density Functional Theory