Activation energy of hydride transfer between isobutane molecules on USY zeolite. First direct experimental measurement by in situ MAS NMR using mixtures of isotopomers

Borghèse, Sophie; Haouas, Mohamed; Sommer, Jean; Taulèlle, Francis

doi:10.1016/j.jcat.2013.05.004

Cited by 17 publications

(14 citation statements)

References 30 publications

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“…The fastest step, which is the hydride transfer k Htr reaction, has an activation energy of 58 kJ mol –1 . This value is comparable with E a estimated by Sommer et al for the hydride transfer occurring with isobutane on USY zeolite (55 kJ mol –1 ). We have found that a similar kinetic step with propane- d 8 on the same ZnO/H-BEA zeolite yielded E a of ca.…”

Section: Resultssupporting

confidence: 89%

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn²⁺ and ZnO) on the Activation of Alkane C–H Bonds

et al. 2020

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With the aim of clarifying the effect of Zn species of different nature (small clusters of ZnO and Zn2+ cations) on the activation of alkane C–H bonds by Zn-modified zeolite, the mechanism of the H/D hydrogen exchange of n-butane-d 10 with Brønsted acid sites (BASs) of ZnO/H-BEA and Zn2+/H-BEA zeolites has been investigated with 1H MAS NMR in situ at 413–468 K. It is established that both ZnO and Zn2+ species provide acceleration of the exchange in the methyl groups with a decreased activation energy compared to the exchange in n-butane on pure acid-form zeolite. The effect of Zn2+ cation is more essential. The acceleration has been attributed to the formation of transient complexes of the alkane methyl groups with Zn species preceding the exchange with BAS. For ZnO/H-BEA, the involvement of the methylene groups in the exchange is related to the alkane dehydrogenation to form butene followed by protonation and hydride shift reaction in the formed butyl cation. For Zn2+/H-BEA zeolite, an enhanced rate of the exchange in the methylene groups is due to the contribution of two pathways: direct exchange with the assistance of Zn2+ cations and through the intermediate formation of n-butene. We have concluded that the observed peculiarities of the kinetics of H/D hydrogen exchange of n-butane on Zn2+/H-BEA and ZnO/H-BEA zeolites could be rationalized in terms of a common kinetic scheme realized for two zeolite samples with different kinetic parameters, rate constants, and activation energies for identical reaction steps.

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Section: Resultssupporting

confidence: 89%

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn²⁺ and ZnO) on the Activation of Alkane C–H Bonds

et al. 2020

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“…In view of the results obtained in this article, the earlier experimentally measured activation energies with MAS NMR for the reactions, performed under conditions of static (batch) reactors, should be re-evaluated. ,,,,,,,,, In each particular case, the equilibrium of the reactant on the catalyst between its adsorbed state and the gas phase should be taken into account to reliably assign E exp to either E app or E int . The findings of this article should also be considered when results of quantum chemical calculations of reaction activation energies ,, are compared with those of the activation energies measured experimentally by MAS NMR in situ. ,, …”

Section: Resultsmentioning

confidence: 99%

“…4,5,10 NMR spectroscopy is being nowadays used for monitoring in situ the kinetics of hydrocarbon transformation on zeolite catalysts. 11 The information about kinetic parameters in the reactions of H/D hydrogen exchange, 12,13 skeletal 14,15 and double-bond isomerization, 16 hydride transfer, 17 alkane aroma-tization, 18 etc. was recently obtained with this method.…”

Section: Introductionmentioning

confidence: 99%

Which Activation Energy Do We Measure? Analysis of the Kinetics of Propene-3-¹³C Double-Bond-Shift Reaction on Silicalite-1 by ¹H MAS NMR In Situ

Arzumanov

Stepanov

2018

J. Phys. Chem. C

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Correct assignment of the experimental activation energy of chemical reactions on solid catalysts to either apparent (E app ) or intrinsic (E int ) activation barriers represents a long-standing problem in the kinetic measurements performed with the use of magic-angle spinning (MAS) NMR spectroscopy in a closed microreactor. Here, the transformation of propene on silicalite-1 has been investigated. It is established that a double-bond-shift reaction represents the main route for propene transformation at 296− 333 K with the involvement of hydrogen-bonded silanol groups as active sites. The kinetics of a double-bond-shift reaction was followed with 1 H MAS NMR spectroscopy in situ by monitoring the 13 C-label transfer in adsorbed propene-3-13 C from the CH 3 group to the CH 2 group. The experimentally measured activation energy E exp for this reaction is discussed in terms of assigning E exp to either apparent (E app ) or intrinsic (E int ) activation barrier. For the correct assignment of E exp , an approach that is based on accounting the adsorption equilibrium established between the reactant in the gas phase and the adsorbed state on the catalyst for the reaction carried out in the batch microreactor is developed. This approach allows the estimation of E int and E app from E exp , provided that the adsorption constant K ads and the adsorption enthalpy H ads are known. On the basis of the developed approach, the experimentally measured E exp of 71 kJ mol −1 has been concluded to represent an intrinsic activation barrier E int for the studied reaction.

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“…NMR is a versatile tool to probe zeolite catalytic chemistry in situ . − There are few if any reports on the use of solid-state NMR for in situ investigation of catalysis in mixed phase comprising a liquid reagent in contact with a zeolite. The etherification reaction of β-citronellene with ethanol to ethers proceeds under such reaction conditions at temperatures as low as 80 °C .…”

Section: Introductionmentioning

confidence: 99%

In Situ Solid-State ¹³C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta

et al. 2016

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The reaction mechanism of etherification of β-citronellene with ethanol in liquid phase over acid zeolite beta is revealed by in situ solid-state (13)C NMR spectroscopy. Comparison of (13)C Hahn-echo and (1)H-(13)C cross-polarization NMR characteristics is used to discriminate between molecules freely moving in liquid phase outside the zeolite and molecules adsorbed inside zeolite pores and in pore mouths. In the absence of ethanol, β-citronellene molecules enter zeolite pores and react to isomers. In the presence of ethanol, the concentration of β-citronellene inside zeolite pores is very low because of preferential adsorption of ethanol. The etherification reaction proceeds by adsorption of β-citronellene molecule from the external liquid phase in a pore opening where it reacts with ethanol from inside the pore. By competitive adsorption, ethanol prevents the undesired side reaction of β-citronellene isomerization inside zeolite pores. β-citronellene etherification on zeolite beta is suppressed by bulky base molecules (2,4,6-collidine and 2,6-ditertiarybutylpyridine) that do not enter the zeolite pores confirming the involvement of easily accessible acid sites in pore openings. The use of in situ solid-state NMR to probe the transition from intracrystalline catalysis to pore mouth catalysis depending on reaction conditions is demonstrated for the first time. The study further highlights the potential of this NMR approach for investigations of adsorption of multicomponent mixtures in general.

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Activation energy of hydride transfer between isobutane molecules on USY zeolite. First direct experimental measurement by in situ MAS NMR using mixtures of isotopomers

Cited by 17 publications

References 30 publications

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn²⁺ and ZnO) on the Activation of Alkane C–H Bonds

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn²⁺ and ZnO) on the Activation of Alkane C–H Bonds

Which Activation Energy Do We Measure? Analysis of the Kinetics of Propene-3-¹³C Double-Bond-Shift Reaction on Silicalite-1 by ¹H MAS NMR In Situ

In Situ Solid-State ¹³C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta

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Activation energy of hydride transfer between isobutane molecules on USY zeolite. First direct experimental measurement by in situ MAS NMR using mixtures of isotopomers

Cited by 17 publications

References 30 publications

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn2+ and ZnO) on the Activation of Alkane C–H Bonds

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn2+ and ZnO) on the Activation of Alkane C–H Bonds

Which Activation Energy Do We Measure? Analysis of the Kinetics of Propene-3-13C Double-Bond-Shift Reaction on Silicalite-1 by 1H MAS NMR In Situ

In Situ Solid-State 13C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta

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Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn²⁺ and ZnO) on the Activation of Alkane C–H Bonds

Mechanism of H/D Hydrogen Exchange of n-Butane with Brønsted Acid Sites on Zn-Modified Zeolite: The Effect of Different Zn Species (Zn²⁺ and ZnO) on the Activation of Alkane C–H Bonds

Which Activation Energy Do We Measure? Analysis of the Kinetics of Propene-3-¹³C Double-Bond-Shift Reaction on Silicalite-1 by ¹H MAS NMR In Situ

In Situ Solid-State ¹³C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta