Radiation chemistry in occluded phases: MCM-41

Werst, D.W.; Choure, Sujata C.; Vinokur, E.I.; Xu, Lan; Trifunac, A. D.

doi:10.1016/s0969-806x(99)00467-3

Cited by 2 publications

(2 citation statements)

References 21 publications

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“…Attempts to generate the EPR spectrum of the 1-methylcyclopentene radical cation in NaZSM5 gave a very poor result, as if adsorption was quite limited. Reported EPR spectra of the radical cation in Freon matrixes 40 and our own experimental results in perfluoromethylcyclohexane 41 show that the hyperfine couplings are quite matrix dependent. Therefore direct comparison of these spectra to the spectrum in HZSM5 is problematic.…”

Section: Resultsmentioning

confidence: 65%

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

et al. 1999

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The formation of H adducts during radiolysis of zeolites containing olefinic and aromatic hydrocarbon guests was demonstrated to occur by H atom transfer from the zeolite to the adsorbed molecules. The H adducts and other paramagnetic radiolysis products (radical cations and H-loss radicals) were detected by EPR spectroscopy. The mechanism of H adduct formation was confirmed by, inter alia, H/D isotopic labeling and comparison of results in HZSM5 and H−Mordenite to results in their Na+-exchanged counterparts. The effects of charge transfer among radiolysis products and zeolite−adsorbate interactions on the relative yields of trapped species is discussed. It is proposed that molecules smaller that a critical size adsorb inhomogeneously in ZSM5, forming aggregates in which ion−molecule reactions occur. Interpretation of the experimental results was aided by quantum chemical calculations of the molecular properties of the intermediates and their reaction energetics. This included evaluation of electron-transfer exothermicities, activation energies for H addition, and the relative acidities of the radical cations.

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Section: Resultsmentioning

confidence: 65%

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

et al. 1999

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“…The mobility of benzene on the MCM-41 surface is also controlled by the density of silanol groups. 37 These measures can be applied in other cases where the ion-molecule nature of the reaction mechanism is in question or exclusion of an ion-molecule reaction channel is desirable.…”

Section: Control Of Radical Cation Reactions In Solidsmentioning

confidence: 99%

Observation of Radical Cations by Swiftness or by Stealth

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Trifunac

1998

Acc. Chem. Res.

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The widespread occurrence of radical cations in chemical processes drives their study under diverse conditions and in every conceivable kind of environment. Radical cations are primary species in ionization events involving highenergy radiation and in photoinduced electron-transfer reactions. They are key intermediates in redox reactions in solution, and they occur on surfaces of strongly oxidizing solid catalysts. To better understand the role played by radical cations in technologically important applications, such as solar energy conversion, catalysis, radiation damage, and the factors that control their reactions, they are studied in neat liquids, concentrated solutions, molecular solids, and heterogeneous solids, on surfaces, and at interfaces. This undertaking requires many different approaches and time scales.What makes the study of radical cations experimentally challenging is their short lifetimes. In nonpolar liquids, most radical cations created by radiolysis undergo geminate recombination with electrons in picoseconds. 1 Recombination can be slowed by use of electron scavengers, increasing solvent polarity (to increase the escape probability for geminate pairs) or viscosity, or virtually stopped altogether by sequestering the charge pairs in a rigid matrix. Besides recombination, fast chemical reactions shorten radical cation lifetimes. Thus, experimental observation of radical cations is based on fast detection techniques and strategies for controlling radical cation reactionssslowing them down, as well as changing the outcome.

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Radiation chemistry in occluded phases: MCM-41

Cited by 2 publications

References 21 publications

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

Observation of Radical Cations by Swiftness or by Stealth

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