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Werst, D.W.; Han, Ping-Hsuan

doi:10.1023/a:1019075814510

Cited by 8 publications

(9 citation statements)

References 31 publications

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“…HZSM5 is a strong Bronsted acid and without care catalytic transformations of the hydrocarbon adsorbates can intrude on the study of radiolytic processes in this zeolite. We have shown that the radiolysis/EPR method can be used effectively to elucidate such catalytic processes and to distinguish between the catalytic effects and genuine radiation chemistry. , Under the conditions of the experiments reported in this study, catalytic reactions of the adsorbates were minimized or in most cases excluded.…”

Section: Methodsmentioning

confidence: 98%

“…Activation-controlled addition of H atoms to pyrene was studied on silica gel by transient optical absorption . We and others reported the formation of H adducts during the radiolysis of hydrocarbons in zeolites, but the formation of H adducts was not studied in depthneither the mechanism nor how it might interact with other reaction channels. − …”

Section: Introductionmentioning

confidence: 99%

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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: Methodsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

et al. 1999

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“…The authors established that the dimerization and isomerization of isobutene on H‐ZSM‐5 zeolite took place as low as 77 K, and cleavage reactions occured even at below room temperature. In the reaction of different cyclic olefins on H‐ZSM‐5 zeolite the formation of radical cations of 1,2‐dimethylcyclopentene was observed in each case 202. The formation of radical cations of differently alkylated bicyclododecenes occurred on H‐mordenite under the same reaction conditions.…”

Section: Epr Spectroscopymentioning

confidence: 76%

In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis

Hunger

Weitkamp

2001

Angewandte Chemie Intl Edit

244

108

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The development of new solid catalysts for use in industrial chemistry has hitherto been based to a large extent upon the empirical testing of a wide range of different materials. In only a few exceptional cases has success been achieved in understanding the overall, usually very complex mechanism of the chemical reaction through the elucidation of individual intermediate aspects of a heterogeneously catalyzed reaction. With the modern approach of combinatorial catalysis it is now possible to prepare and test much more rapidly a wide range of different materials within a short time and thus find suitable catalysts or optimize their chemical composition. Our understanding of the mechanisms of reactions catalyzed by these materials must be developed, however, by spectroscopic investigations on working catalysts under conditions that are as close as possible to practice (temperature, partial pressures of the reactants, space velocity). This demands the development and the application of new techniques of in situ spectroscopy. This review will show how this objective is being achieved. By the term in situ (Lat.: in the original position) is meant the investigation of the chemical reactions which are taking place as well as the changes in the working catalysts directly in the spectrometer.

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“…Die Autoren stellten fest, dass die Dimerisierung und Isomerisierung von Isobuten an H‐ZSM‐5 bereits bei 77 K erfolgt und Spaltungsreaktionen bereits unterhalb von Raumtemperatur ablaufen. Bei der Umsetzung verschiedener cyclischer Olefine an H‐ZSM‐5 wurde jeweils die Bildung der Radikalkationen des 1,2‐Dimethylcylcopentens gefunden 202. Unter den gleichen Reaktionsbedingungen kam es an H‐Mordenit zur Bildung der Radikalkationen verschieden alkylierter Bicyclododecene.…”

Section: Epr‐spektroskopieunclassified

“…Bei der Umsetzung verschiedener cyclischer Olefine an H-ZSM-5 wurde jeweils die Bildung der Radikalkationen des 1,2-Dimethylcylcopentens gefunden. [202] Unter den gleichen Reaktionsbedingungen kam es an H-Mordenit zur Bildung der Radikalkationen verschieden alkylierter Bicyclododecene. Dieses unterschiedliche katalytische Verhalten der verwendeten Festkörperkatalysatoren wurde durch die formselektive Wirkung der Zehnerringporen des Zeoliths H-ZSM-5 erklärt.…”

Section: Epr-untersuchungen Heterogen Katalysierter Oberflächenreaktionenunclassified

In-situ-IR-, -NMR-, -EPR- und -UV/Vis-Spektroskopie: Wege zu neuen Erkenntnissen in der heterogenen Katalyse

Hunger

Weitkamp

2001

Angew. Chem.

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Die Entwicklung neuer Festkörperkatalysatoren für den Einsatz in der industriellen Chemie beruht bisher noch zu einem sehr großen Teil auf dem empirischen Erproben einer Vielzahl unterschiedlicher Materialien. Nur in wenigen Ausnahmefällen ist es gelungen, durch die Aufklärung der einzelnen Teilaspekte einer heterogen katalysierten Reaktion den gesamten, meist sehr komplexen Mechanismus der chemischen Umsetzung zu verstehen. Mit modernen Konzepten der kombinatorischen Katalyseforschung ist es möglich geworden, innerhalb kurzer Zeiträume eine große Zahl unterschiedlicher Materialien zu präparieren und zu testen und damit schneller als vorher geeignete Katalysatoren zu finden oder ihre chemische Zusammensetzung zu optimieren. Unser Verständnis der Mechanismen der von diesen Materialien katalysierten Reaktionen muss jedoch durch spektroskopische Untersuchungen an arbeitenden Katalysatoren unter möglichst praxisnahen Bedingungen (Temperatur, Partialdruck der Reaktanten, Katalysatorbelastung) entwickelt werden. Dies erfordert die Entwicklung und den Einsatz neuer Techniken der In‐situ‐Spektroskopie. Der vorliegende Aufsatz soll zeigen, auf welchen Wegen dieses Ziel erreicht wird. Der Begriff in situ (lat.: an Ort und Stelle) beinhaltet im eigentlichen Sinne die Untersuchung der direkt im Spektrometer ablaufenden chemischen Reaktionen und die mit ihnen verbundenen Veränderungen des Katalysators.

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Cited by 8 publications

References 31 publications

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

Hydrogen Atom Addition to Hydrocarbon Guests in Radiolyzed Zeolites

In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis

In-situ-IR-, -NMR-, -EPR- und -UV/Vis-Spektroskopie: Wege zu neuen Erkenntnissen in der heterogenen Katalyse

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