Formation of radicals and catalytic activity of pentasil-type zeolites in unsaturated hydrocarbon conversions

Slinkin, A. A.; Кучеров, А. В.; Kondratyev, D.A.; Bondarenko, T. N.; Rubinstein, A.M.; Миначев, Х. М.

doi:10.1016/0304-5102(86)85060-x

Cited by 24 publications

(13 citation statements)

References 5 publications

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“…Substantial convergence, after early differences, is obtained for different feed molecules after several reaction steps. Our findings explain the common shape of EPR spectra observed in many different laboratories for C 3 −C 8 olefins on acidic zeolites. − …”

Section: Introductionsupporting

confidence: 79%

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Catalytic Transformations of Olefins on HZSM5 Observed by Radiolysis/EPR

1996

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A new method for elucidating elementary reaction steps in zeolite catalysis was demonstrated for reactions of isobutene and other monoolefins on HZSM5. Radiolysis was used to “spin label” reaction products, and EPR was used for product analysis. The evolution of products was revealed by quenching the reactions cryogenically in a series of equilibration experiments. Isobutene dimerization and isomerization occur on HZSM5 even at 77 K, and cracking occurs below room temperature. The radiolysis/EPR results allow a consistent interpretation of the literature on EPR signals that arise spontaneously upon interaction of acyclic olefins with air-activated H-Mordenite and HZSM5.

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Section: Introductionsupporting

confidence: 79%

“…Finally, the resemblance between our radiolysis/EPR results and the EPR signals that develop when isobutene is adsorbed on air-activated HZSM5 is incontestable. This experiment was carried out by Slinkin et al …”

Section: Discussionmentioning

confidence: 99%

Catalytic Transformations of Olefins on HZSM5 Observed by Radiolysis/EPR

1996

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“…Photoinduced electron transfer in heterogeneous hosts − such as organic assemblies of vesicles and micelles − and porous inorganic solids such as zeolites − and silica gels (or silica) − has been extensively studied with a goal to establish artificial photoredox systems for solar energy conversion and storage. For this purpose, porphyrin derivatives 2a,6c-f,15-17 have been used as photosensitive electron donors due to their structural and functional similarities to chlorophylls and their absorption of visible light.…”

Section: Introductionmentioning

confidence: 99%

“…A photosensitizer of proper molecular size compared to the pore sizes of such inorganic materials can be incorporated into the pores, and the photoinduced radical ions can even be stable at room temperature. Zeolites have been extensively studied as microheterogeneous hosts for efficient photoinduced electron transfer. − Photoinduced electron transfer from Ru(byp) 3 2+ prepared by intracavity synthesis within the supercages of zeolite Y 9 and zeolite X 10 has been reported. Also, aromatic molecules adsorbed on thermally activated zeolite Y 11a,b or ZSM-5 11c,d are readily oxidized to their cation radicals, indicating that the zeolite framework can act as an electron acceptor.…”

Section: Introductionmentioning

confidence: 99%

Photoionization of Porphyrins in Mesoporous Siliceous MCM-41, AlMCM-41, and TiMCM-41 Molecular Sieves

1997

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The photoionization of meso-tetraphenylporphyrin (H2TPP) within mesoporous MCM-41 silica tube molecular sieves is studied with visible light irradiation at room temperature and 77 K. Porphyrin π-cation radicals (H2TPP•+) are generated by photoionization within MCM-41 molecular sieves and are characterized by electron spin resonance (ESR) and diffuse reflectance UV−vis spectroscopy. Mesoporous MCM-41 molecular sieves are shown to be effective heterogeneous hosts to accomplish long-lived net photoinduced electron transfer of bulky porphyrin molecules at room temperature. Siliceous MCM-41 molecular sieves with different pore sizes designated as C n -MCM-41 (C n is the alkyl chain length of the surfactant used in the synthesis) demonstrate a significant pore size effect on the photoionization efficiency of H2TPP. The H2TPP•+ photoyield in C n -MCM-41 measured by ESR increases with increasing C n and is greatest in C16-MCM-41. A series of titanosilicate TiMCM-41 and aluminosilicate AlMCM-41 molecular sieves were synthesized and change the porphyrin photoionization efficiency in comparison with siliceous MCM-41. The photoionization efficiency increases in the order AlMCM-41 < MCM-41 < TiMCM-41. H2TPP•+ radicals are stable in MCM-41 and TiMCM-41 even at room temperature and decay after 30 min photoirradiation by only 5% after 48 h in TiMCM-41 at room temperature.

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“…In the presence of platinum particle the activation energy of hydrogen atom elimination drastically reduces and the reaction energy (DE) for the reverse spillover attains the value of -40 kcal/mol [6,7]. The mechanism of hydrogen transfer upon electron capture may be operative when alkenes and aromatics interact with electron-acceptor sites of high-silica zeolites to form corresponding cation-radicals [19,20].…”

Section: Resultsmentioning

confidence: 98%

A Possible Mechanism of Hydrogen Reverse Spillover in Platinum-Zeolite Catalysts

2008

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Quantum chemical methods (X3LYP and MP2) were applied to investigate the structure and reactivity of anion-radical site in HZSM-5 zeolite. The interaction of hydrogen zeolite with a platinum particle can involve electron transfer to a Brønsted acid site to form an anionradical fragment. A low stability of the latter favors the elimination of atomic hydrogen from the OH-group, an exothermic process with low activation energy. In the metal-zeolite catalysts, the anion-radical fragment formed due to withdrawal of electronic density from the metal particle can be responsible for the reverse spillover of Brønsted hydrogen onto the metal surface.

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Formation of radicals and catalytic activity of pentasil-type zeolites in unsaturated hydrocarbon conversions

Cited by 24 publications

References 5 publications

Catalytic Transformations of Olefins on HZSM5 Observed by Radiolysis/EPR

Catalytic Transformations of Olefins on HZSM5 Observed by Radiolysis/EPR

Photoionization of Porphyrins in Mesoporous Siliceous MCM-41, AlMCM-41, and TiMCM-41 Molecular Sieves

A Possible Mechanism of Hydrogen Reverse Spillover in Platinum-Zeolite Catalysts

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