13C MAS NMR mechanistic study of propane conversion into butanes over H-MFI catalyst

Ivanova, I. I.; Ребров, А. В.; Pomakhina, E. B.; Derouane, Éric G.

doi:10.1016/s1381-1169(98)00254-4

Cited by 20 publications

(2 citation statements)

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“…Propane activation on solid acids related to aromatization, using isotopic tracers, has been reported in several recent mechanistic studies. ,− On the basis of extensive H/D exchange, or 13 C scrambling, observed by in situ solid state NMR in the 200−300 °C temperature range, several authors suggested that the reaction should be governed by a pentacoordinate carbonium ion intermediate as previously demonstrated in liquid HF-SbF 5 superacids. , However, internal hydron scrambling and isotope redistribution between alkane and catalyst is a rather complex mechanism which may imply several pathways with different rates and activation energies. Monitoring the isotope redistribution directly by in situ solid state NMR experiments can be extremely useful. − The competitive pathways, having different activation energies, cannot be distinguished when the temperature necessary to activate propane on zeolites passes above all activation energies.…”

Section: Introductionmentioning

confidence: 89%

The Initial Stages of Solid Acid-Catalyzed Reactions of Adsorbed Propane. A Mechanistic Study by in Situ MAS NMR

et al. 2003

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In situ solid-state NMR spectroscopy was employed to study the kinetics of hydrogen/deuterium exchange and scrambling as well as (13)C scrambling reactions of labeled propane over Al(2)O(3)-promoted sulfated zirconia (SZA) catalyst under mild conditions (30-102 degrees C). Three competitive pathways of isotope redistribution were observed during the course of the reaction: (1) a regioselective H/D exchange between acidic protons of the solid surface and the deuterons of the methyl group of propane-1,1,1,3,3,3-d(6), monitored by in situ (1)H MAS NMR; (2) an intramolecular H/D scrambling between methyl deuterons and protons of the methylene group, without exchange with the catalyst surface, monitored by in situ (2)H MAS NMR; (3) a intramolecular (13)C scrambling, by skeletal rearrangement process, favored at higher temperatures, monitored by in situ (13)C MAS NMR. The activation energy of (13)C scrambling was estimated to be very close to that of (2)H scrambling, suggesting that these two processes imply a common transition state, responsible for both vicinal hydride migration and protonated cyclopropane formation. All pathways are consistent with a classical carbenium ion-type mechanism.

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Section: Introductionmentioning

confidence: 89%

The Initial Stages of Solid Acid-Catalyzed Reactions of Adsorbed Propane. A Mechanistic Study by in Situ MAS NMR

et al. 2003

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“…Monitoring of the transformation of alkanes and alkenes, selectively 13 C-labeled at the specific position of the molecule, with 13 C MAS NMR (MAS – magic angle spinning) allows one to follow the transfer of the 13 C label into the reaction intermediates and products. This results in the identification of the intermediates, establishing their structures, and clarifying the main reaction steps. ,,− Because of high sensitivity and the high speed of data acquisition, FTIR spectroscopy is a valuable tool for studying fast processes such as the initial steps of alkane (alkene) activation on zeolite catalysts. ,,,− The joint use of these spectroscopic methods can help to clarify the roles of BAS and LAS (Lewis acid sites) in the process of isobutene transformation on Zn-containing zeolites and contribute to the determination of the aromatization mechanism. The knowledge obtained about the aromatization mechanism with these spectroscopic methods should promote further investigations in the field of rational catalyst design for the effective utilization of hydrocarbon feedstock to valuable products.…”

Section: Introductionmentioning

confidence: 99%

Isobutene Transformation to Aromatics on Zn-Modified Zeolite: Particular Effects of Zn²⁺ and ZnO Species on the Reaction Occurrence Revealed with Solid-State NMR and FTIR Spectroscopy

et al. 2021

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The effect of Zn 2+ cations and small clusters of ZnO on isobutene transformation to aromatic hydrocarbons on Zn-modified zeolites (Zn 2+ /H-ZSM-5 and ZnO/H-BEA) has been investigated with 13 C MAS NMR and FTIR spectroscopic techniques. It is inferred that isobutene is mainly stabilized in the form of a π-complex with Zn 2+ cations of the Zn 2+ /H-ZSM-5 zeolite at 296−573 K, whereas the oligomerization of the olefin on Brønsted acid sites (BAS) of ZnO/H-BEA occurs at 296 K. Using isobutene, selectively labeled with the 13 C isotope in either CH 2 or C< groups, for NMR analysis of the evolution of the adsorbed species with temperature, the reaction intermediates have been identified within the temperature range of 296− 623 K. At 296 K, an occurrence of the double-bond shift reaction in isobutene on Zn 2+ /H-ZSM-5 and a complete 13 C-label scrambling in the oligomers formed on ZnO/H-BEA have been established. The detected intermediates include a π-complex of the olefin with Zn species, 2-methyl-σ-allylzinc species, isobutene oligomers, and delocalized carbanionic species. It is found that similar intermediates are formed in the course of the reaction on both zeolites at T ≥ 473 K, which implies that similar pathways of isobutene transformation are realized on the zeolites with different Zn species. An analysis of FTIR data reveals that the intermediate species formed on the Zn 2+ /H-ZSM-5 zeolite interact with both BAS and Zn sites at each of the reaction steps of the olefin transformation to aromatic hydrocarbons.

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Isotopic Labeling and Kinetic Isotope Effects

Bauer

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Synthesis and Analysis of Labeled Compounds Kinetic Isotope Effects Applications of Labeled Compounds Carbon Isotopes ( 11 C , 13 C , 14 C ) A Methanol‐to‐Gasoline Reactions; Methylation of Olefins and Aromatics B Isomerization of Alkylaromatics C Isomerization of Olefins and Paraffins D Paraffin Dehydrocyclization E Coke Formation Hydrogen Isotopes ( 2 H , 3 H ) A H / D Exchange of Hydrocarbons over Metal and Acid Catalysts B Deuterium Kinetic Isotope Effects of Hydrocarbon Reactions Oxygen Isotopes ( 17 O , 18 O ) Miscellaneous Isotopes ( 15 N , 29 Si , 35 S ) Conclusions

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13C MAS NMR mechanistic study of propane conversion into butanes over H-MFI catalyst

Cited by 20 publications

References 18 publications

The Initial Stages of Solid Acid-Catalyzed Reactions of Adsorbed Propane. A Mechanistic Study by in Situ MAS NMR

The Initial Stages of Solid Acid-Catalyzed Reactions of Adsorbed Propane. A Mechanistic Study by in Situ MAS NMR

Isobutene Transformation to Aromatics on Zn-Modified Zeolite: Particular Effects of Zn²⁺ and ZnO Species on the Reaction Occurrence Revealed with Solid-State NMR and FTIR Spectroscopy

Isotopic Labeling and Kinetic Isotope Effects

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13C MAS NMR mechanistic study of propane conversion into butanes over H-MFI catalyst

Cited by 20 publications

References 18 publications

The Initial Stages of Solid Acid-Catalyzed Reactions of Adsorbed Propane. A Mechanistic Study by in Situ MAS NMR

The Initial Stages of Solid Acid-Catalyzed Reactions of Adsorbed Propane. A Mechanistic Study by in Situ MAS NMR

Isobutene Transformation to Aromatics on Zn-Modified Zeolite: Particular Effects of Zn2+ and ZnO Species on the Reaction Occurrence Revealed with Solid-State NMR and FTIR Spectroscopy

Isotopic Labeling and Kinetic Isotope Effects

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Isobutene Transformation to Aromatics on Zn-Modified Zeolite: Particular Effects of Zn²⁺ and ZnO Species on the Reaction Occurrence Revealed with Solid-State NMR and FTIR Spectroscopy