Selective isomerization of n-butenes to isobutene on high Si/Al ratio ferrierite in the absence of coke deposits: implications on the reaction mechanism

Asensi, M.A; Martı́nez, Agustı́n

doi:10.1016/s0926-860x(99)00051-4

Cited by 43 publications

(28 citation statements)

References 36 publications

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“…Once the deposits were totally converted to unreactive species, the intrinsic high selectivity of the H-FER was recovered. Note that the current proposal on the role of aromatics formation differs significantly from that of the role of coke reported in other studies (4,(10)(11)(12)(13)(14), in which coke was suggested to hinder oligomers formation by restricting pore dimension or blocking unselective acid sites. On the contrary, our experimental findings strongly support the model recently reported by de Jong et al (8).…”

Section: Relation Between the Carbonaceous Deposits And The Catalyticcontrasting

confidence: 96%

“…Guisnet et al suggested that the isobutene yield was related to the formation of aromatic (5) or tert-butyl (9) carbocations, which catalyzed butene isomerization via a pseudomonomolecular mechanism. However, other authors proposed that the main role of these deposits was to deactivate nonselective sites and/or to increase steric constraint within the microporous solid (4,(10)(11)(12)(13)(14). De Jong et al recently proposed yet another model, in which reactive aliphatic carbonaceous deposits initially yield by-products before being converted to more inert aromatics (8).…”

Section: Introductionmentioning

confidence: 99%

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In Situ IR Study of the Nature and Mobility of Sorbed Species on H-FER during But-1-ene Isomerization

Meunier

Domokos

Seshan

et al. 2002

Journal of Catalysis

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The sorption and reaction of but-1-ene over a ferrierite sample was studied by in situ IR spectroscopy to relate the selectivity to isobutene and the sorbed species. The spectra highlighted the presence of various unsaturated species including polyenes, which were readily formed upon contacting H-FER with but-1-ene while a poor selectivity to isobutene was observed. Aromatic compounds were concluded to be subsequently formed via dehydrogenation/cyclization of the polyenic deposits while the isobutene selectivity increased via suppression of by-products. These data support earlier assumptions that the initial high yield of by-products was produced by the reaction of butenes with reactive deposits, which were gradually converted into more inert aromatic deposits. Upon purging the catalyst with an inert, branched C 8 hydrocarbons and aromatic molecules such as xylenes desorbed. The rates of desorption showed an initially linear variation with the square root of time and were fitted to a monodimensional Fickian model. Because the slowly diffusing species were rather abundant during the course of the reaction, it is proposed that the skeletal isomerization was effectively limited to the acid sites close the pore mouth of H-FER crystallites. c 2002 Elsevier Science (USA)

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Section: Relation Between the Carbonaceous Deposits And The Catalyticcontrasting

confidence: 96%

Section: Introductionmentioning

confidence: 99%

In Situ IR Study of the Nature and Mobility of Sorbed Species on H-FER during But-1-ene Isomerization

Meunier

Domokos

Seshan

et al. 2002

Journal of Catalysis

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“…This indicates that high isobutene selectivity can be obtained without coking. According to the knowledge accumulated thus far, the monomolecular reaction mechanism proposes that the highly isobutene-selective active sites are the modied Brønsted acid sites, 23,46 while the pseudomonomolecular reaction mechanism considers that the highly isobutene-selective active sites are alkylaromatic tertiary carbenium ions on the coke molecules. 24,47,48 In this study, we obtained high isobutene selectivity on fresh nano-sized ferrierite corresponding to the amount of Brønsted acid sites; therefore, a monomolecular reaction mechanism seems more likely.…”

Section: Catalytic Propertiesmentioning

confidence: 99%

Designing ferrierite-based catalysts with improved properties for skeletal isomerization of n-butene to isobutene

et al. 2017

RSC Adv.

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The crystal morphology and size of ferrierite catalysts were controlled by a suite of crystallization methods and structure-directing agents. In particular, nano-sized ferrierite could be obtained by using tetramethylammonium hydroxide and pyrrolidine as double structure-directing agents under dynamic crystallization. The catalysts were analysed by XRD, SEM, N 2 adsorption-desorption, NMR, XRF, NH 3 -TPD, Py-IR, and TGA, and the characteristics were correlated with their catalytic performance in the skeletal isomerization of n-butene. The results clearly indicated that all the catalysts have a similar crystallinity, Si/Al ratio, and total number of acid sites, while a decrease in their crystal size leads to more pore mouth acid sites. The nano-sized ferrierite showed better stability and higher activity, which were related to their crystal morphology, size, and pore mouth acid. In addition, we further confirmed that high isobutene selectivity can be produced by monomolecular reaction.

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“…Asensi et al (14) showed that on a high-silica H-FER (Si/Al = 59, i.e., low numbers of Brønsted acid sites) high isobutene selectivities were reached without the substantial formation of deposits. Recently, an extensive kinetic study by Domokos et al (37) confirmed that the presence of deposits is not crucial for achieving high isobutene selectivities and that isobutene is likely formed over Brønsted acid sites.…”

Section: Relation Between Catalytic Performance and Brønsted Aciditymentioning

confidence: 99%

“…A number of authors (10,(12)(13)(14)(15) therefore suggested a monomolecular reaction pathway, in which butene is isomerized over a plain Brønsted acid site of H-FER, to be the dominant reaction pathway for isobutene formation. The monomolecular formation of isobutene involves an energetically and thermodynamically highly unfavorable primary carbenium ion (16).…”

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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Selective isomerization of n-butenes to isobutene on high Si/Al ratio ferrierite in the absence of coke deposits: implications on the reaction mechanism

Cited by 43 publications

References 36 publications

In Situ IR Study of the Nature and Mobility of Sorbed Species on H-FER during But-1-ene Isomerization

In Situ IR Study of the Nature and Mobility of Sorbed Species on H-FER during But-1-ene Isomerization

Designing ferrierite-based catalysts with improved properties for skeletal isomerization of n-butene to isobutene

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

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