Room‐Temperature Alkane Reactivity in Zeolites: An H/D Exchange Study

Sido, Abdelkarim Sani Souna; Walspurger, Stéphane; Barbiche, Jeremy; Sommer, Jean

doi:10.1002/chem.200902624

Cited by 14 publications

(22 citation statements)

References 46 publications

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“…Combining the results of previous studies [11,32] and the actual ones we can draw the following conclusions. The first step [32] of the mechanism is most probably controlled by some very acidic sites of the zeolite, probably of superacid strength.…”

Section: Resultsmentioning

confidence: 77%

“…To reach the conclusion that the critical intermediates are carbenium ions for the subsequent steps, the use of 2MP for the in situ H/D exchange was essential to lift the ambiguity associated to isobutane, which is too symmetrical, as demonstrated recently. [11] It is, therefore, demonstrated that carbenium is the intermediate entity controlling the rate-determining step. The activation energy found in this study is comparable to the isobutane H/D exchange found in Truitt et al studies [26,38] on H-Beta or HZSM5.…”

Section: Resultsmentioning

confidence: 99%

“…[9] The carbocation intermediates are generally present at very low concentration [10] and thus are difficult to directly detect and observe. We have recently shown [11] that these intermediates are active even at room temperature with zeolites, which substantially facilitates their study. One of the most efficient methods to investigate the reactivity of the alkanes with solid acid catalysts is the isotopic H/D exchange.…”

Section: Introductionmentioning

confidence: 99%

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Low‐Temperature Alkane CH Bond Activation by Zeolites: An In Situ Solid‐State NMR H/D Exchange Study for a Carbenium Concerto

Haouas

Fink

Taulèlle

et al. 2010

Chemistry A European J

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Isotopic H/D exchange has been monitored by in situ MAS NMR spectroscopy of 2-[D(14)]methylpentane with H-USY to probe the controversy over the alkane conversion mechanism. The probe molecule has distinct exchangeable sites with different accessibility to the zeolite surface. In the early stages of the process, the regioselectivity of exchange demonstrates that the slow step of the mechanism is controlled by a carbenium ion intermediate. At a later stage of exchange, intramolecular hydride migrations, typical of carbenium chemistry, replace D by H also on other carbon atoms, resulting in a loss of regioselectivity. Therefore, the first and the subsequent steps of the H/D exchange proceed at this temperature through a carbenium intermediate species.

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Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low‐Temperature Alkane CH Bond Activation by Zeolites: An In Situ Solid‐State NMR H/D Exchange Study for a Carbenium Concerto

Haouas

Fink

Taulèlle

et al. 2010

Chemistry A European J

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“…[3][4][5][6][7][8][9][10]13 NMR is a quantitative technique allowing direct determination of the relative concentration of the species contained in a sample, and absolute concentration using internal or external standards. Besides the reactant molecules, solid catalysts possess NMR active nuclei (isotopes with nuclear spin I a 0) being 29 Si, 27 Al, 31 P, 1 H, 13 C,. .…”

Section: In Situ Solid State Nmr Spectroscopymentioning

confidence: 99%

“…27,29 The activation mechanism of branched alkanes, especially isobutane, on Brønsted acid sites of solid catalysts at ambient or lower temperature is also controversial. 26,[30][31][32][33] In situ solid state 1 H NMR spectroscopy was used to study the H/D exchange of deuterated isobutane on zeolite H-ZSM-5 in the absence of impurities of alkenes. 26,30 The results are described in Fig.…”

Section: Activation Of Alkanes At Low Temperature: H/d Exchange Exper...mentioning

confidence: 99%

Insights into reaction mechanisms in heterogeneous catalysis revealed by in situ NMR spectroscopy

Blasco

2010

Chem. Soc. Rev.

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This tutorial review intends to show the possibilities of in situ solid state NMR spectroscopy in the elucidation of reaction mechanisms and the nature of the active sites in heterogeneous catalysis. After a brief overview of the more usual experimental devices used for in situ solid state NMR spectroscopy measurements, some examples of applications taken from the recent literature will be presented. It will be shown that in situ NMR spectroscopy allows: (i) the identification of stable intermediates and transient species using indirect methods, (ii) to prove shape selectivity in zeolites, (iii) the study of reaction kinetics, and (iv) the determination of the nature and the role played by the active sites in a catalytic reaction. The approaches and methodology used to get this information will be illustrated here summarizing the most relevant contributions on the investigation of the mechanisms of a series of reactions of industrial interest: aromatization of alkanes on bifunctional catalysts, carbonylation reaction of methanol with carbon monoxide, ethylbenzene disproportionation, and the Beckmann rearrangement reaction. Special attention is paid to the research carried out on the role played by carbenium ions and alkoxy as intermediate species in the transformation of hydrocarbon molecules on solid acid catalysts.

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