Isomerisation of butene in isobutene on ferrierite catalyst: A mono- or a bimolecular process?

Mériaudeau, P.; Bacaud, R.; Hung, Le Ngoc; Anh, Vu Thi Ngoc

doi:10.1016/1381-1169(96)00156-2

Cited by 81 publications

(55 citation statements)

References 3 publications

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“…Over a fresh catalyst 13 C-labeling experiments have proven that nonselective bimolecular reactions, i.e., dimerization followed by cracking, dominate the catalytic action. However, in the same experiments it was established that over an aged catalyst with carbonaceous deposits present, the formation of isobutene occurs selectively and must take place via a different route (8,10,11).…”

Section: Introductionmentioning

confidence: 99%

Probing the Accessible Sites for n-Butene Skeletal Isomerization over Aged and Selective H-Ferrierite with d3-Acetonitrile

Donk

Bus

Broersma

et al. 2002

Journal of Catalysis

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Aged H-ferrierite (H-FER) samples with different contents of de-posits were prepared and studied under differential catalytic conditions in a tapered element oscillating microbalance. Subsequently, these samples were examined using infrared spectroscopy to determine the nature of carbonaceous deposits and probing the type and number of accessible sites with d 3 -acetonitrile. From these results, for the first time, we have been able to calculate turnover frequencies (TOFs) for n-butene conversion and isobutene formation for both fresh and aged H-FER catalysts. It is observed that the deposition of carbonaceous species significantly lowers the number of accessible Brønsted sites. With short time on stream (TOS), cracking of the alkyl-aromatic deposits contributes to the overall isobutene production but simultaneously harms the selective catalytic action by inducing nonselective side reactions. With prolonged TOS these deposits become nonreactive and as a result the TOF drops, while isobutene is produced with high selectivity. It is demonstrated that at this stage no carbenium ions are detected, while Brønsted OH acid sites are still accessible for d 3 -acetonitrile on the extensively aged and highly selective H-FER. This indicates that the latter sites are responsible for the selective catalytic conversion of n-butene into isobutene. c 2002 Elsevier Science (USA)

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Section: Introductionmentioning

confidence: 99%

Probing the Accessible Sites for n-Butene Skeletal Isomerization over Aged and Selective H-Ferrierite with d3-Acetonitrile

Donk

Bus

Broersma

et al. 2002

Journal of Catalysis

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“…This autocatalytic reaction allows rapid and selective transformation of one molecule of n-butene into one molecule of isobutene. This is a pseudo-monomolecular process, which could, therefore, explain why no 13 C scrambling is observed in n-butene isomerization over aged FER samples [32,33]. The maximum observed in the isobutene yield in the case of alumina (Fig.…”

Section: Origin Of the Increase With Time On-stream Of The Selectivitmentioning

confidence: 91%

Selective Skeletal Butene Isomerization Through a Bimolecular Mechanism

Benazzi

Travers

Gnep

et al. 1999

Oil & Gas Science and Technology - Rev. IFP

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Résumé -Isomérisation bimoléculaire sélective du n-butene en isobutene -La transformation du n-butène a été étudiée en réacteur dynamique à 350°C sur des zéolithes à taille de pore intermédiaire (H-FER, H-TON, H-EU-1 et H-MFI) et à 500°C sur alumine. Sur les catalyseurs frais, l'isobutène mais aussi le propène et les pentènes sont directement formés (produits primaires), ce qui démontre que l'isomérisation de squelette du n-butène se produit au moins en partie par des étapes successives d'oligomérisation, isomérisation et craquage (mécanisme bimoléculaire). Les différences importantes de sélectivité entre les catalyseurs sont dues à de nombreux facteurs : participation ou non d'intermédiaires trimères, limitations dans la désorption des produits branchés, etc. Sur tous les catalyseurs, la sélectivité en isobutène augmente avec le temps de travail. Cette augmentation s'explique par un nouveau mode d'isomérisation très sélectif impliquant comme intermédiaires des triméthylpentènes formés par réaction du n-butène sur des molécules d'isobutène retenues dans les pores de la ferrierite. Cette réaction autocatalytique rend très sélective en isobutène la transformation bimoléculaire du n-butène.Mots-clés : butènes, isomérisation de squelette, mécanisme, zéolithe, alumine, sites actifs. Abstract -Selective Skeletal Butene Isomerization through a Bimolecular Mechanism -n-Butene transformation was carried out at 350°C over medium pore size zeolites (H-FER, H-TON, H-EU-1 and H-MFI) and at 500°C over alumina. With fresh catalysts, not only isobutene but also propene and pentenes are primary products, which indicates that at least some of the butene isomerization occurs through oligomerizationisomerization-cracking steps (bimolecular mechanism). The large differences in selectivity are due to many factors, including whether or not trimer intermediates participate in the mechanism and limited product desorption. All the catalysts exhibit increasing isobutene selectivity with increasing time on-stream. This increase in selectivity can be explained by the selective isomerization of n-butene through a reaction process whose first step is the formation of trimethylpentene intermediates from isobutene product and n-butene reactant. This autocatalytic reaction can render the bimolecular transformation of n-butenes very selective to isobutene.

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“…41 The catalytically active Brønsted acid sites of zeolites were modeled by the cluster H 3 Si(OH)AlH 2 (OSiH 3 ) shown in Figure 1e. The cluster approach has proven to be quite useful in studies of the mechanisms of zeolite-catalyzed reactions (see ref [17][18][19][20][21][22][23][24] in the paper of Viruela-Martin et al, 36 reviews, [23][24][25] and recent works, e.g. of Evleth et al 42 and Blaszkowski et al 43 ).…”

Section: Models and Computational Detailsmentioning

confidence: 99%

“…Isomerization of n-butenes on the H/FER zeolite represents an interesting example: the bimolecular mechanism occurs on the fresh zeolite samples, but on the aged catalyst the monomolecular process becomes predominant, resulting in much better selectivity toward iso-butene. 18,19 The monomolecular isomerization in turn might occur in two ways: via the one-step methyl shift or via the "protonated cyclopropane" mechanism. It is difficult to distinguish between these two cases on the grounds of the experimental data, but arguments of Olah's carbocation theory 20 have provided some insight on this subject.…”

Section: Introductionmentioning

confidence: 99%

“…conversion of n-butenes to iso-butene and n-alkane hydroisomerization, this reaction influences the product distribution of the cracking and alkylation processes. Extensive experimental studies of skeletal isomerization have been performed, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and it has been found that this reaction proceeds via either a monomolecular or bimolecular (dimerization/cracking) mechanism.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Density Functional and Hartree−Fock Calculations on the Cyclopropane Ring Intermediates Involved in the Zeolite-Catalyzed Skeletal Isomerization of Hydrocarbons and in the Carbon Isotope Scrambling in 2-Propyl Cation

et al. 1997

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Quantum-chemical calculations were carried out on the mechanism of the zeolite-catalyzed hydrocarbon skeletal isomerization via the cyclopropane ring intermediates. According to the B3LYP/6-31G* calculations, formation of cyclopropane from surface alkoxy species in zeolites occurs via a transition state whose hydrocarbon part resembles a corner-protonated cyclopropane (corner-PCP) ring. Two conformations of the transition state found differ in the orientation of the PCP portion with respect to the acid site. The activation energy for the cyclopropane ring closure reaction is found to be rather sensitive to the use of planar symmetry constraints and to the level of calculations and less sensitive to the level of the geometry optimization. Calculations on the mechanism of the carbon isotope scrambling in the free 2-propyl cation were also performed, at several theory levels up to the Gaussian-2 model. The relatively stable intermediates of this superacid-catalyzed reaction are carbocations, in contrast to the zeolite-catalyzed isotope scrambling where the relatively stable intermediates are surface alkoxy species with the corner-protonated cyclopropane as a high-energy transition state.

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Isomerisation of butene in isobutene on ferrierite catalyst: A mono- or a bimolecular process?

Cited by 81 publications

References 3 publications

Probing the Accessible Sites for n-Butene Skeletal Isomerization over Aged and Selective H-Ferrierite with d3-Acetonitrile

Probing the Accessible Sites for n-Butene Skeletal Isomerization over Aged and Selective H-Ferrierite with d3-Acetonitrile

Selective Skeletal Butene Isomerization Through a Bimolecular Mechanism

Density Functional and Hartree−Fock Calculations on the Cyclopropane Ring Intermediates Involved in the Zeolite-Catalyzed Skeletal Isomerization of Hydrocarbons and in the Carbon Isotope Scrambling in 2-Propyl Cation

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